Micro 130 chp 21

bullae (

vesicles larger than 1 cm in diameter

Malaria

Malaria is characterized by chills and fever and often by vomiting and severe headache. These symptoms typically appear at intervals of 2 to 3 days, alternating with asymptomatic periods occurs wherever the Anopheles mosquito vector is found and there are human hosts for the Plasmodium protozoan Occasionally, malaria has been transmitted by unsterilized syringes used by drug addicts. Blood transfusions from people who have been in an endemic area are also a potential risk Four species of Plasmodium cause malaria in humans. Plasmodium vivax is widely distributed because it can develop in mosquitoes at a lower temperature and is the cause of the most prevalent form of malaria. "benign" malaria, the cycle of paroxysms (recurrent intensifications of symptoms) occurs every 2 days, and the patients generally survive even without treatment important factor in the life cycle of P. vivax is that it can remain dormant in the liver of the patient for months and even years P. ovale and P. malariae also cause a relatively benign malaria, but even so, the victims lack energy. These latter two malarial types are lower in incidence and rather restricted geographically most dangerous malaria is that caused by P. falciparum. Perhaps one reason for the virulence of this type of malaria is that humans and the parasite have had less time to become adapted to each other. It is believed that humans have been exposed to this parasite (through contact with birds) only in relatively recent history. "malignant" malaria, untreated it eventually kills about half of people infected; More red blood cells (RBCs) are infected and destroyed than in other forms of malaria. The resulting anemia severely weakens the victim. Furthermore, the RBCs develop surface knobs that cause them to stick to the walls of the capillaries, which become clogged. This clogging prevents the infected RBCs from reaching the spleen, where phagocytic cells would eliminate them. The blocked capillaries and subsequent loss of blood supply leads to death of the tissues. Kidney and liver damage is caused in this fashion. The brain is frequently affected, and P. falciparum is the usual cause of cerebral malaria Malaria and its symptoms are intimately related to the protozoan's complex reproductive cycle Infection is initiated by the bite of a mosquito, which carries the sporozoite stage of the Plasmodium protozoan in its saliva. About 300 to 500 sporozoites enter the bloodstream of the bitten human and within about 30 minutes enter the liver cells. The sporozoites in the liver cells undergo reproductive schizogony by a series of steps that finally results in the release of about 30,000 merozoite forms into the bloodstream. The merozoites infect RBCs. Within the RBCs they again undergo schizogony, and after about 48 hours, the RBCs rupture and each releases about 20 new merozoites diagnosis of malaria is usually made by examining a blood smear for infected RBCs. With the release of the merozoites there is also a simultaneous release of toxic compounds, which is the cause of the paroxysms of chills and fever that are characteristic of malaria. The fever reaches 40°C, and a sweating stage begins as the fever subsides. B/ paroxysms, the patient feels normal. Many of the released merozoites infect other RBCs within a few seconds to renew the cycle in the bloodstream. If only 1% of the RBCs contain parasites, an estimated 100 billion parasites will be in circulation at one time in a typical malaria patient. Some of the merozoites develop into male or female gametocytes. When these enter the digestive tract of a feeding mosquito, they pass through a sexual cycle that produces new infective sporozoites People who survive malaria acquire a limited immunity. can be reinfected, but have a less severe form of the disease. This relative immunity almost disappears if the person leaves an endemic area with its periodic reinfections Malaria is especially dangerous during pregnancy because adaptive immunity is suppressed.

ischemia

an inadequate blood supply to an organ or part of the body, especially the heart muscles. the wound becomes anaerobic. Ischemia leads to necrosis, or tissue death The death of soft tissue resulting from the loss of blood supply is called gangrene

Cytomegalovirus (CMV)

Almost all of us will become infected with Cytomegalovirus (CMV) during our lifetime very large herpesvirus that, much like the Epstein-Barr virus, probably remains latent in white blood cells, such as monocytes, neutrophils, and T cells It is not much affected by the immune system, replicating very slowly and escaping antibody action by moving between cells that are in contact Carriers of the virus may shed it in body secretions such as saliva, semen, and breast milk When CMV infects a cell, it causes the formation of distinctive inclusion bodies that are visible by microscopy. When these bodies occur in pairs, they are known as "owl's eyes" and are useful in diagnosis. The cells were also enlarged, a condition known as cytomegaly, from which the virus eventually received its name. This disease of the newborns was given the name of cytomegalic inclusion disease (CID) official name is human herpesvirus 5. In the United States, about 8000 infants each year are born suffering symptomatic damage from CID, the most serious of which includes severe mental retardation or hearing loss If the mother is already infected before conception, the rate of transmission to a fetus is less than 2%, but if the primary infection occurs during pregnancy, the rate of transmission is in the range of 40-50% Tests to determine the immune status of the mother are available, and it's recommended that physicians determine the immune status of female patients of childbearing age All non-immune women should be informed of the risks of infection during pregnancy. A complicating factor is that women who are CMV positive before conception might still be infected with new strains of CMV and transmit it to the fetus In healthy adults, acquiring a CMV infection causes either no symptoms or those resembling a mild case of infectious mononucleosis. It has been said that if CMV were accompanied by a skin rash, it would be one of the better-known childhood diseases. It is therefore not surprising, given that 80% of the population of the United States is estimated to carry the virus, that CMV is a common opportunistic pathogen in persons whose immune systems have become compromised In developing parts of the world, infection rates of CMV approach 100%. For immunocompromised individuals, CMV is a frequent cause of a life-threatening pneumonia, but almost any organ can be affected About 85% of AIDS patients exhibit a CMV-caused eye infection, Cytomegalovirus retinitis. Without treatment, it results in eventual loss of vision. To prevent transmission of CMV during transplantation procedures, an immunoglobulin preparation containing a standardized amount of antibody is recommended For treatment of CMV illness, ganciclovir has been the mainstay. A suitable alternative, if resistance to this antiviral develops, is foscarnet CMV is transmitted mostly by activities that result in contact with body fluids that contain the virus, such as kissing, and it is very common among children in day-care settings. It can also be transmitted sexually, by transfused blood, and by transplanted tissue. Transmission by transfused blood can be eliminated by filtering out the white cells from the blood or by serological testing of the donor for the virus. Transplanted tissue is usually tested for the virus, and products are now available that contain antibodies to neutralize CMV present in donated tissue. Vaccines are under development, but none is currently available.

cutaneous diphtheria

Diphtheria is also expressed as cutaneous diphtheria. C. diphtheriae infects the skin, usually at a wound or similar skin lesion, and there is minimal systemic circulation of the toxin In cutaneous infections, the bacteria cause slow-healing ulcerations that are covered by a gray membrane Cutaneous diphtheria is fairly common in tropical countries.

papules

Raised lesions; also called blemishes.

Prions of nervous system

Several fatal diseases affecting the human central nervous system are caused by prions. The shape of an enzyme's protein component is essential for its operation. A certain protein is normally found on the surface of brain cell neurons and is even found on the surface of certain stem cells in red bone marrow and cells that become neurons; called normal prion protein, PrPC. Its function is uncertain, but there is evidence that it may guide maturation of nerve cells. Certainly, the protein's shape causes no damage. But this protein can assume two folded shapes, one normal and the other abnormal (there is no change in the amino acid sequence). If the PrPC encounters an abnormally folded protein, the normal protein changes its shape and also becomes abnormally folded—this is called PrPSc. In fact, a chain reaction of protein misfolding occurs. Therefore, a single infective prion may lead to a cascade of new prions, which then clump together to form the fibril aggregations of misfolded proteins that are found in diseased brains Autopsies of this infected brain tissue also show that it exhibits a characteristic spongiform degeneration (it is porous, like a sponge). In recent years, the study of these diseases, called transmissible spongiform encephalopathies (TSE), has been one of the most interesting areas of medical microbiology A typical prion disease in animals is sheep scrapie, which has been long known in Great Britain and made its first appearance in the United States in 1947. The infected animal scrapes itself against fences and walls until areas of its body are raw. During a period of several weeks or months, the animal gradually loses motor control and dies. The infection can be experimentally passed to other animals by injecting brain tissue from one animal to the next A prion disease, chronic wasting disease, affects wild deer and elk in the western United States and Canada. It is invariably fatal, and there are concerns that it might infect humans who eat venison and might eventually infect domestic livestock. Humans suffer from TSE diseases similar to scrapie; Creutzfeldt-Jakob disease (CJD) is an example. CJD is rare (about 300 cases per year in the United States). It often occurs in families, an indication of a genetic component. This form of CJD is sometimes referred to as classic CJD to differentiate it from similar variants that have appeared. There is no doubt that an infective agent is involved because transmission via corneal transplants and accidental scalpel nicks of a surgeon during autopsy have been reported. Several cases have been traced to the injection of a growth hormone derived from human tissue. Boiling and irradiation have no effect, and even routine autoclaving is not reliable. This has led to suggestions that surgeons use disposable instruments where there is a risk of exposure to CJD. To sterilize reusable instruments, the WHO currently recommends a strong solution of sodium hydroxide combined with extended autoclaving at 134°C. However, there are reports that applications of a simple cleaning detergent combined with protease enzymes to disrupt the prions may prove an effective solution to the problem. Some tribes in New Guinea have suffered from a TSE disease called kuru (a native word for shaking or trembling). Transmission of kuru is apparently related to the practice of cannibalistic rituals. Carleton Gajdusek received the Nobel Prize for Physiology and Medicine in 1976 for his investigations of kuru

cholera

The causative agent of cholera, one of the most serious gastrointestinal diseases, is Vibrio cholerae, a slightly curved, gramnegative rod with a single polar flagellum grow in the small intestine and produce an exotoxin, cholera toxin that causes host cells to secrete water and electrolytes, especially potassium The result is watery stools containing masses of intestinal mucus and epithelial cells As much as 12 to 20 liters (3 to 5 gallons) of fluids can be lost in a day, and the sudden loss of these fluids and electrolytes causes shock, collapse, and often death. The blood, lacking fluids, may become so viscous that vital organs are unable to function properly Violent vomiting generally also occurs. The microbes are not invasive, and a fever is usually not present Untreated cases of cholera may have a mortality rate of 50%, although with proper supportive care it is usually less than 1% diagnosis is based upon symptoms and culturing of V. cholerae from feces. Cholera bacteria, and other members of the genus Vibrio in general, are strongly associated with brackish (salty) waters characteristic of estuaries, although they are also readily spread in contaminated freshwater form biofilms and colonize copepods (tiny crustaceans), algae, and other aquatic plants and plankton, which aids their survival Under unfavorable conditions, V. cholerae may become dormant; the cell shrinks into a nonculturable, spherical state. A favorable change in the environment causes them to revert rapidly to the culturable form. Both forms are infectious cholera bacteria are exceptionally sensitive to stomach acids. Persons with impaired stomach acid secretion or who are taking antacids are at higher risk of infection Recovery from cholera results in an effective immunity, but only to bacterial strains of the same antigenic characteristics. The serogroup O:1, which caused a pandemic in the 1880s, is known as the classical strain. A later pandemic was caused by a biotype of O:1 named El Tor Until the 1990s it was thought that only V. cholerae O:1 caused epidemic cholera, but a widespread epidemic in India and Bangladesh by a new serogroup, O:139, changed this view. There are also nonepidemic strains of V. cholerae, non-O:1/O:139, that are only infrequently associated with large-scale outbreaks of cholera. They occasionally cause wound infections or sepsis, especially in people with liver disease or who are immunosuppressed. Available oral vaccines provide immunity of relatively short duration and only moderate effectiveness. The most effective therapy is intravenous replacement of the lost fluids and electrolytes. As much as 10% of the patient's body weight within a few hours may be required. Rehydration therapy is so effective that in Bangladesh, for example, where cholera is common, deaths are considered "unusual." Severe cholera may be treated with doxycycline.

Zika virus disease (ZVD)

is caused by the Zika virus, or ZIKV, a member of the Flaviviridae. It is transmitted primarily through the bite of infected Aedes spp. mosquitoes, the same mosquitoes that carry the viruses that cause dengue fever, yellow fever, and chikungunya. Zika virus may also be transmitted sexually, from mother to child during pregnancy and delivery, and through blood transfusions. ZIKV was first discovered in 1947 in rhesus monkeys and is named after the Zika forest in Uganda. It was subsequently identified in humans in 1952 in the United Republic of Tanzania. The first outbreak outside Africa occurred in Micronesia, on the island of Yap. The virus moved to French Polynesia and Brazil in 2014. The virus reached the continental United States in 2015 (Figure 22.14). Since then, 224 locally contracted cases have been reported. The most common signs and symptoms of ZVD, which last about a week, affect about 20% of infected individuals. They are usually mild and include fever, headache, muscle and joint pain, malaise, skin rash, and conjunctivitis. Because people usually do not become ill enough to require hospitalization, they may not even realize that they are infected. However, ZIKV infection during pregnancy greatly increases the risk of fetuses and infants developing a condition called microcephaly. In this disorder, the infant's head is much smaller than normal because of abnormal brain development. Infants so affected exhibit developmental delays that range from mild to severe. ZVD is also associated with Guillain-Barré syndrome, a temporary muscular Weakness and tingling in the upper and lower limbs. Diagnosis of ZVD is confirmed by reverse transcriptase PCR, and treatment involves rest, intake of sufficient fluids, and pain and fever reduction with common medications. In 2016, the National Institute of Allergy and Infectious Diseases began human testing of a DNA vaccine (see page 503). As with arboviral encephalitis, the best prevention is reducing mosquito-breeding sites and reducing contact between mosquitoes and humans

African trypanosomiasis

African trypanosomiasis, or sleeping sickness, is a protozoan disease that affects the nervous system Even today, estimates are that as many as half a million Africans are infected, and there are about 100,000 new cases yearly. caused by two subspecies of Trypanosoma brucei that infect humans: Trypanosoma brucei gambiense and T.b. rhodesiense They are morphologically indistinguishable but differ significantly in their epidemiology—that is, in their ability to infect nonhuman hosts Humans are the only significant reservoir for T.b. gambiense, whereas T.b. rhodesiense is a parasite of domestic livestock and many wild animals These protozoans are flagellates that are spread by tsetse fly vectors T.b. gambiense is transmitted by a tsetse fly species that inhabits stream vegetation, where there are also concentrations of human populations. It is distributed throughout west and central Africa and is sometimes termed West African trypanosomiasis. More than 97% of reported cases in humans are of this type. Once a person becomes infected, there are few symptoms for weeks or months. Eventually, a chronic form of disease with fever, headaches, and a variety of other symptoms develops that indicates involvement and deterioration of the CNS. Coma and death are inevitable without effective treatment. In contrast, infections by T.b. rhodesiense are transmitted by species of tsetse flies that inhabit savannahs (grasslands with scattered trees) of eastern and southern Africa. Wild animals inhabiting these areas are well adapted to the parasite and are little affected, but humans and domestic animals become acutely ill Infections of humans follow a more acute course than that caused by T.b. gambiense; symptoms of illness are apparent within a few days or so of infection. Death occurs within weeks or a few months, sometimes from cardiac problems even before the CNS is affected. Typanosomiasis is treated with suramin and pentamidine, but these do not alter the course of the disease once the CNS is affected. The drug that does alter the disease's course, melarsoprol, is very toxic. Eflornithine crosses the blood-brain barrier and blocks an enzyme required for proliferation of the parasite. It requires an extended series of injections, but it is so dramatically effective against even late stages of T.b. gambiense that it has been called the resurrection drug. (Its effectiveness against T.b. rhodesiense is variable; melarsoprol is still recommended.) The current primary approach in combating the disease is to attempt elimination of the vector, the tsetse fly. The use of tentlike, insecticide-treated traps that mimic the color and odor of animal hosts of the insect, combined with large-scale releases of sterile males have eliminated the tsetse fly on the offshore island of Zanzibar The insect is a weak flyer, and health care officials hope to repeat this eradication on selected areas of the mainland A vaccine is being developed, but a major obstacle is that the trypanosome is able to change protein coats at least 100 times and can thus evade antibodies aimed at only one or a few of the proteins. Each time the body's immune system is successful in suppressing the trypanosome, a new clone of parasites appears with a different antigenic coat

septicemia

growth of bacteria in the blood

encephalitis

inflammation of the brain

Haemophilus influenzae Meningitis

aerobic, gram-negative bacterium, common member of the normal throat microbiota when it enters the bloodstream and causes several invasive diseases. In addition to causing meningitis, it is also frequently a cause of pneumonia, otitis media, and epiglottitis carbohydrate capsule of the bacterium is important to its pathogenicity, especially those bacteria with capsular antigens of type b. (Strains that lack a capsule are called nontypable.) Medically, the bacterium is often referred to by the acronym Hib Haemophilus refers to the need the microorganism has for factors in blood for growth (hemo = blood; philus = loving) Hib-caused meningitis occurs mostly in children under age 4, especially at about 6 months, when antibody protection provided by the mother weakens incidence is decreasing because of the Hib vaccine, which was introduced in 1988 H. influenzae meningitis has accounted for most of the cases of reported bacterial meningitis (45%), with a mortality rate of about 6%.

Cytomegalovirus (CMV) infections

caused by another type of human herpes virus, are the most important cause of congenital infection in developed countries. Transmission to the fetus is highest if the mother acquires the infection during the first half of pregnancy. In the United States, about one out of every 150 babies is born with congenital CMV infection. However, only about 20% of infected babies will be sick. Symptoms of congenital CMV include microcephaly, hearing and vision loss, and seizures.

skins microbiota

contain relatively large numbers of gram-positive cocci, such as staphylococci and micrococci. These bacteria tend to be resistant to dry environments, and to the high osmotic pressures found in concentrated salt or sugar solution gram-positive pleomorphic rods called diphtheroids. Some diphtheroids, such as Cutibacterium (Propionibacterium) acnes, are typically anaerobic and inhabit hair follicles. Their growth is supported by secretions from the oil glands (sebum), produce propionic acid, which helps maintain the low pH of skin, generally between 3 and 5

Arboviral Encephalitis

Encephalitis caused by mosquito-borne viruses (called arboviruses) is rather common in the United States. (Arbovirus is short for arthropod-borne virus. This terminology represents a functional grouping; it is not a formal taxonomic term.) The incidence of disease increases in the summer months, coinciding with the proliferation of adult mosquitoes. Sentinel animals, such as caged chickens, are tested periodically for antibodies to arboviruses. This gives health officials information on the incidence and types of viruses in their area. A number of clinical types of arboviral encephalitis have been identified; all can cause symptoms ranging from subclinical to severe, including rapid death. Active cases of these diseases are characterized by chills, headache, and fever. As the disease progresses, mental confusion and coma occur. Survivors may suffer from permanent neurological problems. Horses as well as humans are affected by these viruses; thus, there are strains causing eastern equine encephalitis (EEE) and western equine encephalitis (WEE). These two viruses are the most likely to cause severe disease in humans. EEE is the more severe; the mortality rate is 30% or more, and survivors experience a high incidence of brain damage, deafness, and other neurological problems. EEE is uncommon (its main mosquito vector prefers to feed on birds); only about 100 cases a year are reported. No cases of WEE have been reported in over 10 years; it has a mortality rate of 5%. St. Louis encephalitis (SLE) acquired its name from the location of an early major outbreak (in which it was originally discovered that mosquitoes are involved in the transmission of these diseases). SLE is distributed from southern Canada to Argentina, but mostly in the central and eastern United States. Fewer than 1% of people infected exhibit symptoms; it can, however, be a severe disease with a mortality rate in symptomatic patients of about 20%. California encephalitis (CE) was first identified in that state, but most cases occur elsewhere. In fact, there has been only one case of CE in California in 60 years. A relatively mild illness, it is seldom fatal. A new arbovirus disease, now the most common arbovirus in the United States (Figure 22.13), was introduced into the United States in 1999. First reported in the New York City area, it was quickly identified as being caused by West Nile virus (WNV), which, like the virus causing SLE, is related to the virus causing Japanese encephalitis (see page 638). The disease is maintained in a bird-mosquito-bird cycle. The primary mosquito is a species of Culex, which can overwinter as adults in temperate climates. Birds serve as amplifying hosts; some species, such as house sparrows, can have high levels of viremia without dying. But mortality of infected crows, ravens, and blue jays is high, and public health officials sometimes request reports of dead birds of these species. Most human cases of WNV are subclinical or mild, but the disease can cause a polio-like paralysis or fatal encephalitis, especially in older adults. Other encephalitis viruses are appearing in the United States. As of 2017, 30 cases of Heartland virus disease (a member of the Bunyaviridae) have occurred in the United States is unknown. Infections by human Powassan virus (POW, a member of the Flaviviridae) have been recognized in northern latitudes. In the United States, POW virus disease has been reported primarily from northeastern states and the Great Lakes region. See Diseases in Focus 22.2 on page 641 for a summary of the predominant arbovirus-caused diseases of the United States The Far East and South Asia also have endemic arboviral encephalitis. Japanese encephalitis is the best known; it is a serious public health problem, especially in Japan, Thailand, Korea, China, and India. Vaccines are used to control the disease in these countries and are often recommended for visitors. Only about 1% of people infected show clinical symptoms, which may involve seizures and paralysis—and a mortality rate of 20-30%. Arboviral encephalitis is diagnosed by serological tests, usually ELISA tests to identify IgM antibodies. The most effective preventive measure is local control of the mosquitoes.

Plague

Vector-borne diseases Few diseases have affected human history more dramatically than plague dark blue areas of skin caused by hemorrhages caused by a gram-negative, rod-shaped bacterium, Yersinia pestis Normally a disease of rats, plague is transmitted from one rat to another by the rat flea, Xenopsylla cheopis In the far West and Southwest, the disease is endemic in wild rodents, especially ground squirrels and prairie dogs. If its host dies, the flea seeks a replacement host, which may be another rodent or a human, It can jump about 9 cm A plague-infected flea is hungry for a meal because the growth of the bacteria forms a biofilm that blocks the flea's digestive tract, and the blood the flea ingests is quickly regurgitated. An arthropod vector is not always necessary for plague transmission. Contact from the skinning of infected animals; scratches, bites, and licks by domestic cats; and similar incidents have been reported to cause infection. In the United States, exposure to plague is increasing, as residential areas encroach on areas with infected animals. In parts of the world where human proximity to rats is common, infection from this source still prevails. From the flea bite, bacteria enter the human's bloodstream and proliferate in the lymph and blood. One factor in the virulence of the plague bacterium is its ability to survive and proliferate inside phagocytic cells rather than being destroyed by them The lymph nodes in the groin and armpit become enlarged, and fever develops as the body's defenses react to the infection. Such swellings, called buboes, account for the name bubonic plague. This is the most common form, comprising 80-95% of cases today. The mortality rate of untreated bubonic plague is 50-75%. Death, if it occurs, is usually within less than a week after the appearance of symptoms. particularly dangerous condition called septicemic plague arises when the bacteria enter the blood and proliferate, and cause bleeding into the skin and other organs and septic shock Eventually, the blood carries the bacteria to the lungs, and a form of the disease called pneumonic plague results. The mortality rate for this type of plague is nearly 100% . Even today, this disease can rarely be controlled if it isn't recognized within 12 to 15 hours of the onset of fever. People can become infected from inhaling respiratory droplets after close contact with domestic cats and humans with pneumonic plague Plague is established in the ground squirrel and prairie dog communities in the western states, seven cases are reported annually, most resulting from flea bites most commonly diagnosed by isolating the bacterium and then sending it to a laboratory for identification. A rapid diagnostic test, however, can reliably detect the presence of the capsular antigen of Y. pestis in blood and other fluids of patients within 15 minutes even under remote field conditions People exposed to infection can be given prophylactic antibiotic protection. A number of antibiotics, including gentamicin and fluoroquinolones, are effective Recovery from the disease confers reliable immunity. A vaccine is available for people likely to come into contact with infected fleas during field operations or for laboratory workers exposed to the pathogen.

"emerging" hemorrhagic fevers

In 1967, 31 people became ill and 7 died after contact with some African monkeys that were imported into Europe. The virus was strangely shaped (in the form of a filament [filovirus]) and was named for the site of the laboratory outbreak in Germany, the Marburg virus, or green monkey virus. The symptoms of infection by hemorrhagic viruses are mild at first; headache and muscle pain. But after a few days the victim suffers from high fever and begins vomiting blood and bleeding profusely, both internally and from external openings such as the nose and eyes. Death comes in a few days from organ failure and shock A similar hemorrhagic fever, Lassa fever, appeared in west Africa in 1969 and was traced to a rodent reservoir. The Lassa virus, an arenavirus, is present in the rodent's urine and is the source of human infections. Outbreaks of Lassa fever have killed thousands. Seven years later, outbreaks in Africa of another highly lethal hemorrhagic fever were caused by Ebolavirus, a filovirus similar to the Marburg virus. The walls of the blood vessels are damaged, the virus interferes with coagulation, and blood leaks into surrounding tissue. Named Ebola virus disease (EVD) or Ebola with mortality approaching 90%. The natural host reservoir for Ebolavirus is probably a cave-dwelling fruit bat, which is used as food and is not acutely affected by the virus it carries. Once a human is infected and shedding blood, the infection is spread by contact with the blood and body fluids and in many cases by the reuse of needles used on patients. In 2016, a recombinant vaccine composed of live vesicular stomatitis virus carrying Ebolavirus glycoprotein was shown to be 100% effective in phase 3 clinical trials involving 10,000 people. The vaccine will likely be used in a ring-containment approach. Ring containment consists of identifying people with the infection, vaccinating everyone who has had contact with them, and then vaccinating people in surrounding areas South America has several hemorrhagic fevers caused by Lassa-like viruses (arenaviruses) that are maintained in the rodent population. Argentine and Bolivian hemorrhagic fevers are transmitted in rural areas by contact with rodent excretions Whitewater Arroyo virus, an arenavirus with a reservoir in wood rats in southwestern states. These are the first reports of arenaviruscaused hemorrhagic disease in the Northern Hemisphere. Hantavirus pulmonary syndrome, caused by the Sin Nombre virus,* a bunyavirus, has become well known in the United States because of several outbreaks, mostly in the western states. It manifests itself as a frequently fatal pulmonary infection, in which the lungs fill with fluids. The main treatment is mechanical respiration; the antiviral ribavirin is recommended, but its value is uncertain. best known there as hemorrhagic fever with renal syndrome and primarily affects renal (kidney) function All these related diseases are transmitted by the inhalation of viruses in dried urine and feces from infected small rodents Worldwide, there are at least 14 known disease-causing hantaviruses

Q Fever

In 2015, six Americans were diagnosed with Q fever after being injected with fetal sheep cells in Germany; xenotransplant has unsubstantiated claims of improving vitality (anti-aging) causative agent the obligately parasitic, intracellular bacterium Coxiella burnetii; a member of the gammaproteobacteria It has the ability to multiply intracellularly Most intracellular bacteria, such as rickettsia, are not resistant enough to survive airborne transmission, but this microorganism is an exception wide range of clinical symptoms, and systematic testing shows that about 60% of cases are not even symptomatic Cases of acute Q fever usually feature symptoms of high fever, headaches, muscle aches, and coughing. A feeling of malaise may persist for months heart becomes involved in about 2% of acutely ill patients and is responsible for the rare fatalities In cases of chronic Q fever, the best known manifestation is endocarditis. Some 5 to 10 years might elapse between the initial infection and the appearance of endocarditis; and, because these patients show few signs of acute disease, the association with Q fever is often missed Antibiotic therapy and earlier diagnosis lowered the mortality rate from chronic Q fever to under 5% C. burnetii is a parasite of several arthropods, especially cattle ticks, and it is transmitted among animals by tick bites Infected animals include cattle, goats, and sheep, as well as most domestic mammalian pets In animals the infection is usually subclinical microbes are shed in the feces, milk, and urine of infected cattle. Once the disease is established in a herd, it is maintained by aerosol transmission. The disease is spread to humans by ingesting unpasteurized milk and by inhaling aerosols of microbes generated in dairy barns Inhaling a single pathogen is enough to cause infection, and many dairy workers have acquired at least subclinical infections endospore-like body was discovered, which may account for this heat resistance, body resembles the elementary body of chlamydiae more than typical bacterial endospores Diagnosis is based on an increasing titer of antibodies against Coxiella. The pathogen can be identified by isolation and growth in chick embryos in eggs or in cell culture testing for Coxiella-specific antibodies in a patient's serum can use serological tests disease is endemic to California, Arizona, Oregon, and Washington A vaccine for laboratory workers and other high-risk personnel is available Doxycycline has been recommended for treatment. When growth within macrophages in chronic infections renders C. burnetii resistant, the killing activity can be restored by combining doxycycline with chloroquine, an antimalarial. The chloroquine raises the pH of the phagosome, increasing doxycycline's efficiency.

fungal infections in nervous system

The central nervous system is seldom invaded by fungi. However, one pathogenic fungus in the genus Cryptococcus is well adapted to growth in CNS fluids

Incidence and Treatment of Botulism

Botulism is not a common disease. Only a few cases are reported each year About half the cases are type A, and types B and E account about equally for the balance Alaskan native people probably have the highest rate of botulism in the world, mostly of type E. The problem arises from food preparation methods that reflect a cultural tradition of avoiding the use of scarce fuels for heating or cooking. For example, one food involved in Alaskan outbreaks of botulism is muktuk. To tenderize them, they are stored anaerobically in a container of seal oil for several weeks until they approach putrefaction. Botulism organisms do not seem to be able to compete successfully with the normal intestinal microbiota, so the production of toxin by ingested bacteria almost never causes botulism in adults. However, the intestinal microbiota of infants is not well established, and they may suffer from infant botulism. Nearly 100 cases occur in the United States annually, several times more than any other form of botulism. Although infants have ample opportunity to ingest soil and other materials contaminated with the endospores of the organism, many reported cases have been associated with honey. Endospores of C. botulinum are recovered with some frequency from honey, and a lethal dose may be as few as 2000 bacteria. The recommendation is not to feed honey to infants under 1 year of age; there is no problem with older children or adults who have normal intestinal microbiota For treatment of botulism in infants, a special preparation is available, BabyBIG®. The acronym BIG represents Botulism Immune Globulin. The immune globulin consists of antibodies to botulism toxin that have been derived from human sources. Botulism is diagnosed by inoculating mice with samples from patient serum, stool, or vomitus specimens. Different sets of mice are immunized with type A, B, or E antitoxin. All the mice are then inoculated with the test toxin; if, for example, those protected with type A antitoxin are the only survivors, then the toxin is type A. The toxin in food can similarly be identified by mouse inoculation The botulism pathogen can also grow in wounds in a manner similar to that of clostridia causing tetanus or gas gangrene, such episodes of wound botulism occur occasionally. The treatment of botulism relies heavily on supportive care. Recovery requires that the nerve endings regenerate; it therefore proceeds slowly. Extended respiratory assistance may be needed, and some neurological impairment may persist for months. Antibiotics are of almost no use because the toxin is preformed. Antitoxins aimed at neutralizing A, B, and E toxins are available and are usually administered together. This trivalent antitoxin will not affect the toxin already attached to the nerve endings and is probably more effective on type E than on types A and B. The antitoxin used in adults is derived from horses and has serious side effects, including serum sickness (immune complexes formed by reaction with antigens in the antitoxin) and potential anaphylaxis

Fungi in lower respitory system

Fungi often produce spores that are disseminated through the air. therefore several serious fungal diseases affect the lower respiratory system The rate of fungal infections has been increasing in recent years Opportunistic fungi are able to grow in immunosuppressed patients, and AIDS, transplant drugs, and anticancer drugs have created more immunosuppressed people than ever before.

Chronic Hepatitis B

Most individuals suffering from acute hepatitis B clear the virus successfully, but some fail to do so and develop chronic hepatitis B People infected when very young are most likely to become chronic carriers. The risk for infants is about 90%; in children of 1 to 5 years, about 25-50%. Adolescents and young adults have a much lower risk, only 6-10% Overall, up to 10% of infected patients become chronic carriers of the virus For some, the condition is essentially asymptomatic: they are considered inactive carriers and have a low risk of progressing to clinical disease. Many others suffer from malaise, loss of appetite, and general fatigue—but usually without evidence of jaundice In cases in which the chronic infection results in liver cirrhosis, the patient is seriously ill. Tests of liver function usually follow, leading to a diagnosis. Liver cancer develops in some cases. In fact, liver cancer is the most prevalent form of cancer in sub-Saharan Africa and East Asia, areas where hepatitis B is extremely common in high-prevalence (Asian) countries, HBV infection tends to be acquired around the time of birth (perinatal) from infected mothers. As a consequence, the immune system doesn't recognize a difference between the virus and the host, and a high level of immunologic tolerance ensues. Because of this tolerance, the infection isn't accompanied by acute hepatitis; instead, a chronic, usually lifelong infection is established. This is the case in about 90% of infected persons. In spite of the immunologic tolerance to HBV, some liver injury occurs, and there is a high risk of death from liver disease, especially among men in low-prevalence (Western) countries, most acute infections by HBV occur from exposure to infected blood or other body fluids. It is often a disease of young adults participating in risky behaviors—injecting street drugs or sexual promiscuity, for example. Long-term intimate nonsexual contact with an infected individual can also transmit HBV. Infected people who are immunocompetent develop a strong immune response, and the virus is cleared in all but about 1% of those infected. These patients have a much lower incidence of chronic disease and of liver cancer The diagnosis of HBV is usually based on symptoms, followed by tests of liver function. Serological tests can detect HBV antigens and antibodies. The presence of hepatitis B surface antigen (HBsAg) indicates the presence of the virus in the blood. After the virus is cleared, anti-HBsAg appears, and the patient is considered immune Detection of the hepatitis B "e" antigen (HBeAg), a marker for the core of the virus, usually means that the virus is replicating vigorously. If this antigen disappears and is replaced by antibodies against it, this usually means that liver disease associated with viral reproduction has diminished. It also means that the patient is less infectious to others HBV is transmitted through sexual contact; needles, syringes, or other drug-injection equipment; and from mother to baby at birth Transmission from mother to infant can be prevented by administering hepatitis B immune globulin (HBIG) to the newborn immediately after birth. These babies should also be vaccinated available HBV vaccines use HBsAg produced by a genetically modified yeast no specific treatment for acute HBV. For chronic HBV infection, there are currently seven approved treatments. However, none of these is reliably curative, largely because the DNA of the virus becomes integrated into the genome of the host aim of treatment for chronic HBV infections is to diminish the DNA of the virus to levels that are undetectable with a PCR assay. Treatment decisions are made on the basis of several factors, such as patient age and the stage of the disease. Coinfections with HIV often occur and complicate treatment. Available antivirals include alpha interferon as well as several nucleoside analogues, such as lamivudine, adefovir, entecavir, telbivudine, and tenofovir DF course of treatment typically extends over several months. Combinations of at least two drugs are recommended to minimize development of resistance. Liver transplantation is often a final option in treatment.

Nongonococcal urethritis (NGU)

Nongonococcal urethritis (NGU), also known as nonspecific urethritis (NSU), refers to any inflammation of the urethra not caused by Neisseria gonorrhoeae Symptoms include painful urination and a watery discharge.

Shiga-toxin-producing E. coli (STEC)

Some E. coli strains that produce Shiga-like toxins are termed Shiga-toxin-producing E. coli (STEC) True Shiga toxin is produced only by Shigella dysenteriae. Most outbreaks are due to EHEC serotype O157:H7. Other lesser known strains include O121 and O104:H21 Bc the toxin is released upon the cell's lysis, antibiotic therapy can worsen the attack by causing the release of more toxin Cattle, which are not affected by the pathogen, are the main reservoir; infections are spread by contaminated food or water. Currently, 10-30% of domestic cattle carry STEC, which contaminate the carcass at slaughter requirements for testing ground meats for the presence of this strain of E. coli, especially if intended for export. Leafy vegetables may also be contaminated, sometimes by runoff from feedlots. infectious dose is estimated to be very small, probably fewer than 100 bacteria About 6% of infected people develop inflammation of the colon (the last part of the large intestine, ending just above the rectum) involving profuse bleeding, called hemorrhagic colitis Unlike Shigella, these E. coli bacteria don't invade the intestinal wall, but rather release the toxin into the intestinal lumen (space) Another dangerous complication is hemolytic uremic syndrome (HUS). Characterized by blood in the urine, often leading to kidney failure, HUS occurs when the kidneys are affected by the toxin. Some 5-10% of young children who have been infected progress to this stage, which has a mortality rate of about 5%. Management of these patients primarily involves intravenous rehydration and careful monitoring of serum electrolytes. Some survivors of HUS may require kidney dialysis or even transplants A standard method is to use media that differentiate E. coli O157 bacteria by their inability to ferment sorbitol In 2016, an ELISA test was developed by the USDA to identify Shiga-toxin-producing strains Vaccines that greatly lower the numbers of O157: H7 bacteria in cattle are available, but it is uncertain whether they will find widespread use.

tapeworm

The life cycle of a typical tapeworm extends through three stages. The adult worm lives in the intestine of a human host, where it produces eggs that are excreted in the feces (see Figure 12.28, page 353). The eggs are ingested by animals such as grazing cattle, where the egg hatches into a larval form called a cysticercus (plural: cysticerci) that lodges in the animal's muscles. Human infections by tapeworms begin with the consumption of undercooked beef, pork, or fish containing cysticerci. The cysticerci develop into adult tapeworms that attach to the intestinal wall by suckers on the scolex (see Figure 12.27, page 352). The adult beef tapeworm, Taenia saginata (TE-ne--ah sa-jinAH-tah), seldom causes significant symptoms beyond a vague abdominal discomfort. However, psychological distress can result when a meter or more of detached segments (proglottids) occasionally break loose and unexpectedly slip out of the anus. Taenia solium (SO- -le--um), the pork tapeworm, has a life cycle similar to that of the beef tapeworm. An important difference is that T. solium may produce the larval stage in the human host. Taeniasis develops when the adult tapeworm infects the human intestine. This is a generally benign, asymptomatic condition, but the host continuously expels eggs of T. solium, which contaminate hands and food under poor sanitary conditions. Cysticercosis, infection with the larval stage, can develop when humans or swine ingest T. solium eggs. These eggs can leave the digestive tract and develop into larvae that lodge in tissue (usually brain or muscles). Cysticerci in muscle tissue are relatively benign and cause few serious symptoms, but the larvae occasionally lodge in an eye, causing ophthalmic cysticercosis and affecting vision (Figure 25.21). The most serious, and much more common, disease is neurocysticercosis, which arises when the larvae develop in areas of the central nervous system, such as the brain. Neurocysticercosis, which is endemic in Mexico and Central America, has become a fairly common condition in parts of the United States with large Mexican and Central American immigrant populations. The symptoms often mimic those of epilepsy or a brain tumor. The number of cases reported reflects, in part, the use of computed tomography (CT) scanning or magnetic resonance imaging (MRI) in diagnosis. In endemic areas, neurological patients can be screened with serological tests for antibodies to T. solium. The fish tapeworm Diphyllobothrium latum (dI - ¿fil-lo- -BAHthre- -um LA- -tum) is found in pike, trout, perch, and salmon. The CDC has issued warnings about the risks of fish tapeworm infection from sashimi and sushi (Japanese dishes prepared from raw fish), foods that have become increasingly popular. To relate a vivid example, about 10 days after eating, one person developed symptoms of abdominal distention, flatulence, belching, intermittent abdominal cramping, and diarrhea. Eight days later, the patient passed a tapeworm 1.2 m (4 ft) long, identified as a species of Diphyllobothrium Laboratory diagnosis of tapeworms consists of identifying the tapeworm eggs (Figure 25.22a and b) or segments in feces. Adult tapeworms in the intestinal stage can be eliminated with antiparasitic drugs such as praziquantel and niclosamide. Cases of neurocysticercosis can sometimes be treated with drugs, but these often worsen the situation, and surgery may be required to remove cysticerci.

crevicular fluid

a tissue exudate, is similar to serum and contains phagocytic cells and immunoglobulin which can lower bacterial numbers.

Treponema pallidum

causes congenital syphilis, which can result in miscarriage, stillbirth, and early infant death. The fetus is susceptible to infection after the fourth month of pregnancy. Surviving infants may show altered bone development. In the United States, approximately 429 cases were reported in 2016. Penicillin taken by the mother is 98% effective in preventing the disease.

Zika virus disease

crosses the placenta during pregnancy and targets nerve stem cells. It is linked to microcephaly, calcium deposits in the brain, and other brain and eye abnormalities.

staphylococcal food poisoning,

leading cause of gastroenteritis is staphylococcal food poisoning, an intoxication caused by ingesting an enterotoxin produced by S. aureus Staphylococci are comparatively resistant to environmental stresses, fairly high resistance to heat; vegetative cells can tolerate 60°C for half an hour. Their resistance to drying and radiation helps them survive on skin surfaces. Resistance to high osmotic pressures helps them grow in foods, such as cured ham, in which the high osmotic pressure of salts inhibits the growth of competitors S. aureus is often an inhabitant of the nasal passages, from which it contaminates the hands. It's also a frequent cause of skin lesions on the hands If the microbes are allowed to incubate in the food, a situation called temperature abuse, they reproduce and release enterotoxin into the food. These events, which lead to outbreaks of staphylococcal intoxication produces several toxins that damage tissues or increase the microorganism's virulence The production of the toxin of serological type A (which is responsible for most cases) is often correlated with the production of an enzyme that coagulates blood plasma. Such bacteria are described as coagulasepositive No direct pathogenic effect can be attributed to the enzyme, but it is useful in the tentative identification of types that are likely to be virulent growth of the microbe is facilitated if the competing microorganisms in the food have been eliminated—by cooking, for example. It is also more likely to grow if competing bacteria are inhibited by a higher-than-normal osmotic pressure or by a relatively low moisture level tends to outgrow most competing bacteria under these conditions. Custards, cream pies, and ham are examples of high-risk foods. Competing microbes are minimized in custards by the high osmotic pressure of sugar and by cooking. In ham they are inhibited by curing agents, such as salts and preservatives. Bc food contamination by human handlers can't be avoided completely, the most reliable method of preventing staphylococcal food poisoning is adequate refrigeration during storage to prevent toxin formation The toxin itself is heat stable and can survive up to 30 minutes of boiling. Therefore, once the toxin is formed, it is not destroyed when the food is reheated, although the bacteria will be killed mortality rate of staphylococcal food poisoning is almost zero among otherwise healthy people, but it can be significant in weakened individuals, such as residents of nursing homes short incubation time characteristic of intoxication. If the food hasn't been reheated so the bacteria are still alive, the pathogen can be recovered and grown. S. aureus isolates can be tested by phage typing, a method used in tracing the source of the contamination Pathogenic staphylococci usually ferment mannitol, produce hemolysins and coagulase, and form golden-yellow colonies. They cause no obvious spoilage when growing in foods. Detecting the toxin in food samples has always been a problem; there may be only 1 to 2 nanograms in 100 g of food.

systemic inflammatory response syndrome (SIRS)

overwhelming inflammatory response in the absence of infection causing relative hypovolemia and decreased tissue perfusion caused by a focus of infection that releases mediators of inflammation into the bloodstream. The site of the infection itself is not necessarily the bloodstream, and in about half of the cases no microbes can be found in the blood

septic shock

A final stage, when low blood pressure can no longer be controlled by addition of fluids More than one million cases occur each year in the United States with a fatality rate of 28-50%

acute bacterial endocarditis

A more rapidly progressive type of bacterial endocarditis is acute bacterial endocarditis, which is usually caused by Staphylococcus aureus The organisms find their way from the initial site of infection to normal or abnormal heart valves; the rapid destruction of the heart valves is frequently fatal within a few days or weeks if untreated. Streptococci can also cause pericarditis, inflammation of the sac around the heart (the pericardium)

enterotoxigenic E. coli (ETEC)

A pathogenic group of E. coli called enterotoxigenic E. coli (ETEC) secretes enterotoxins that cause diarrhea frequently fatal for children under 5 one of the enterotoxins ETEC produces resembles the cholera toxin in function. ETEC bacteria are not invasive and remain in the intestinal lumen

cyclosporiasis

A protozoan named Cyclospora cayetanensis. The symptoms of cyclosporiasis are a few days of watery diarrhea, but in some cases it may persist for weeks Most outbreaks have been associated with the ingestion of oocysts in water, on contaminated berries, or similar uncooked foods contaminated by oocysts shed in human feces or possibly from birds in the field Diagnosis is by acid-fast staining of feces. Oocysts can also be detected using fluoresence microscopy bc the oocysts are naturally fluorescent There is really no satisfactory test to detect contamination of foods The antibiotic combination of trimethoprim and sulfamethoxazole is used for treatment

Amebic dysentery (amebiasis)

Amebic dysentery, or amebiasis, is spread mostly by food or water contaminated by cysts of the protozoan ameba Entamoeba histolytica stomach acid can destroy trophozoites, it does not affect the cysts In the intestinal tract, the cyst wall is digested away, and the trophozoites are released. They then multiply in the epithelial cells of the wall of the large intestine. severe dysentery results; the feces characteristically contain blood and mucus. The trophozoites feed on tissue in the gastrointestinal tract Severe bacterial infections result if the intestinal wall is perforated. Abscesses might have to be treated surgically, and the invasion of other organs, particularly the liver, is not uncommon Perhaps 5% of the U.S. population are asymptomatic carriers of E. histolytica. Worldwide, one person in ten is estimated to be infected, mostly asymptomatically, and about 10% of these infections progress to the more serious stages Diagnosis largely depends on recovering and identifying the pathogens in feces. (Red blood cells, ingested as the parasite feeds on intestinal tissue and observed within the trophozoite stage of an ameba, help identify E. histolytica.) Several EIA serological tests are available. Such tests are especially useful when the affected areas are outside the intestinal tract and the patient is not passing amebae Metronidazole is the drug of choice in treatment.

Therapy for Sepsis

An effective therapy for sepsis is a medical priority and will probably require entirely new approaches. symptoms of sepsis are largely caused by the body's response to the infection, a response that has been described as being "unhelpfully exuberant." Any agent that would suppress this response would be independent of the source of the infection. Even in the absence of such therapies, the care of patients with sepsis has improved, and the mortality rate in recent years has declined but is still around 28%.

anthrax

Bacillus anthracis, the bacterium that causes anthrax in animals endospore-forming bacillus is a large, aerobic, gram-positive microorganism that is apparently able to grow slowly in soil types that meet specific moisture conditions The endospores have survived in soil tests for up to 60 years. The disease strikes primarily grazing mammals, such as cattle and sheep. The B. anthracis endospores are ingested along with grasses, causing a fulminating, fatal sepsis human anthrax is now rare in the United States. People at risk are those who handle animals, hides, wool, and other animal products from certain foreign countries Infections by B. anthracis are initiated by endospores. Once introduced into the body, they are taken up by macrophages, where they germinate into vegetative cells. These are not killed, but multiply, eventually killing the macrophage. The released bacteria then enter the bloodstream, replicate rapidly, and secrete toxins. The primary virulence factors of B. anthracis are two exotoxins. Both toxins share a third toxic component, a cell receptor- binding protein called the protective antigen, that binds the toxins to target cells and permits their entry. One toxin, the edema toxin, causes local edema (swelling) and interferes with phagocytosis by macrophages. The other toxin, lethal toxin, specifically targets and kills macrophages, which disables an essential defense of the host the capsule of B. anthracis is very unusual. It is not a polysaccharide but rather is composed of amino acid residues, which for some reason do not stimulate a protective response by the immune system. Therefore, once the anthrax bacteria enter the bloodstream, they proliferate without any effective inhibition until there are tens of millions per milliliter. These immense populations of toxin-secreting bacteria ultimately kill the host. Anthrax affects humans in three forms: cutaneous anthrax, gastrointestinal anthrax, and inhalational (pulmonary) anthrax Antibiotics are effective in treating anthrax if they are administered in time. Currently recommended drugs are doxycycline or ciprofloxacin plus one or two additional agents that are known to be active against the pathogen recent development in the treatment of symptomatic inhalational anthrax is the use of raxibacumab, which inhibits the formation of toxin. This monoclonal antibody has proven to be effective in animal studies. People who have been exposed to anthrax endospores can be given preventive doses of antibiotics for a time as a precaution. This time period is usually quite long because experience has shown that up to 60 days can elapse before the inhaled endospores germinate and initiate active disease Vaccination of livestock against anthrax is a standard procedure in endemic areas. A single dose of an effective live, attenuated vaccine is used, which is considered unsafe for use in humans. The only vaccine currently approved for use in humans contains an inactivated form of the protective antigen toxin and is designed to prevent entry of the other two toxins into the host's cells. This vaccine requires a series of five injections over a period of 18 months, followed by annual boosters. Three doses of the vaccine over 4 weeks, along with antibiotic treatment, are recommended for people who have been exposed to B. anthracis. Diagnosis of anthrax has usually consisted of isolating and identifying B. anthracis from a clinical specimen—which is too slow for detecting bioterrorism outbreaks. A blood test can detect both inhalational and cutaneous cases of anthrax within an hour. Furthermore, locations such as a few mailsorting facilities are being equipped with automated electronic sensors that can immediately detect anthrax spores

Bacterial diseases of the Reproductive System

Bacteria are the causative agents in about 20% of all STIs Most bacterial STIs will not cause harm; however, some have the potential to cause serious health problems if not diagnosed and treated early. Bacterial STIs can be successfully treated with antibiotics.

Blastomycosis (North American blastomycosis)

Blastomycosis is usually called North American blastomycosis to differentiate it from a similar South American blastomycosis. It is caused by the fungus Blastomyces dermatitidis, a dimorphic fungus endemic in soil around the Great Lakes and Mississippi River Valley most infections are asymptomatic, begins in the lungs after inhalation of conidiospores. It resembles bacterial pneumonia and can spread rapidly. Cutaneous ulcers commonly appear when the yeast are disseminated in circulating monocytes. Abscesses may form, with extensive tissue destruction The pathogen can be isolated from pus and biopsy specimens. Itraconazole or amphotericin B is usually an effective treatment.

dysentary

Both infections and intoxications often cause diarrhea, which most of us have experienced Severe diarrhea accompanied by blood or mucus is called dysentery. Both types of digestive system diseases are also frequently accompanied by abdominal cramps, nausea, and vomiting Diarrhea and vomiting are both defensive mechanisms designed to rid the body of harmful material

Hand-Foot-and-Mouth Disease

Caused by several enteroviruses, hand-foot-and-mouth disease is spread by contact with mucous or saliva of an infected person It most commonly occurs among children in day care, preschool, and kindergarten usual incubation is 3-7 days, with initial symptoms of fever followed by sore throat. Soon after, a rash (either flat or raised) appears on areas such as the hands, feet, mouth, tongue, and interior cheeks occasionally—when the disease is caused by Enterovirus 71—it can be accompanied by neurological conditions such as encephalitis, meningitis, and even a paralysis resembling polio. Adults with normal immune systems are less likely to be infected. There is no treatment

Inclusion Conjunctivitis

Chlamydial conjunctivitis, or inclusion conjunctivitis, is quite common today caused by Chlamydia trachomatis, a bacterium that grows only as an obligate intracellular parasite. In infants, who acquire it in the birth canal, the condition tends to resolve spontaneously in a few weeks or months, but in rare cases it can lead to scarring of the cornea Chlamydial conjunctivitis also appears to spread in the unchlorinated waters of swimming pools; in this context, it is called swimming pool conjunctivitis. Tetracycline applied as an ophthalmic ointment is an effective treatment.

macules

Flat, reddened lesions

Viruses in the Lower Respitory System

For a virus to reach the lower respiratory system and initiate disease, it must pass numerous host defenses designed to trap and destroy it numerous respiratory ailments are caused by viruses. Rapid PCR kits that can identify several respiratory viruses are available

Prophylaxis for malaria

For travel to the few areas in which the Plasmodium is still sensitive to it, chloroquine is the drug of choice. In chloroquine-resistant areas, a combination of atovaquone and proguanil is the best tolerated. Travelers to malarial areas are often prescribed mefloquine. It requires only a weekly dosage, but users must be cautioned about serious side effects. These include dizziness and loss of balance, which may become permanent. Some of the psychiatric symptoms, such as depression and hallucinations, may persist for years, even after the drug is no longer being used.

Haemophilus influenzae Pneumonia

Haemophilus influenzae is a gram-negative coccobacillus, and a Gram stain of sputum will differentiate this type of pneumonia from pneumococcal pneumonia Children under 5 and adults over 65 are most at risk for infection Hib vaccine has reduced the incidence in children by 99%. Diagnostic identification of the pathogen uses special media that determine requirements for X and V factors Third-generation cephalosporins are resistant to the b-lactamases produced by many H. influenzae strains and are therefore usually the drugs of choice.

Herpetic Keratitis

Herpetic keratitis is caused by the same herpes simplex type 1 virus (HSV-1) that causes cold sores and is latent in the trigeminal nerves infection of the cornea, often resulting in deep ulcers, and that may be the most common cause of infectious blindness in the United States The drug trifluridine is often an effective treatment.

Ehrlichiosis

Human monocytotropic ehrlichiosis (HME) is caused by Ehrlichia chafeensis a gramnegative, rickettsia-like, obligately intracellular bacterium. Aggregates of bacteria—called morulae, the Latin word for mulberry—form within the cytoplasm of monocytes E. chafeensis was first observed in a human case in 1986; previously it had been considered a solely veterinary pathogen HME is a tickborne disease; the common name for the usual vector is the Lone Star tick. Cases occasionally occur where this tick is not found, so there may be other vectors. The white-tailed deer is the main animal reservoir, but it does not show signs of illness

enterohemorrhagic E. coli (EHEC)

In recent years, strains of enterohemorrhagic E. coli (EHEC) have caused several outbreaks of serious disease in the United States The primary virulence factor in these bacteria is a Shigalike toxin. Shiga toxins are a family of toxins that are closely related

Primary Stage Syphilis

In the primary stage of the disease, the initial sign is a small, hard-based chancre, or sore, which appears at the site of infection 10 to 90 days following exposure—on average, about 3 weeks. The chancre is painless, and an exudate of serum forms in the center. This fluid is highly infectious, and examination with a darkfield microscope shows many spirochetes. In a couple of weeks, this lesion disappears. None of these symptoms causes any distress In fact, many women are entirely unaware of the chancre, which is often on the cervix. In men, the chancre sometimes forms in the urethra and isn't visible During this stage, bacteria enter the bloodstream and lymphatic system, which distribute them widely in the body

lymphangitis

Infection and inflammation of the lymphatic vessels visible as red streaks under the skin, running along the arm or leg from the site of the infection

sinuses

Infection of a sinus involving heavy nasal discharge of mucus is called sinusitis If the opening by which the mucus leaves the sinus becomes blocked, internal pressure can cause pain or a sinus headache These diseases are almost always self-limiting, meaning that recovery will usually occur even without medical intervention.

Bacterial vaginitis

Inflammation of the vagina due to infection, or vaginitis, is most commonly caused by one of several organisms: mainly the fungus Candida albicans, the protozoan Trichomonas vaginalis, or the bacterium Gardnerella vaginalis, a small, pleomorphic gramvariable rod Most of these cases are attributed to the presence of G. vaginalis and are termed bacterial vaginosis. (Because there is no sign of inflammation, the term vaginosis is preferred to vaginitis) The condition is something of an ecological mystery. It's believed that bacterial vaginosis is precipitated by some event that decreases the number of vaginal Lactobacillus bacteria that normally produce hydrogen peroxide This competitive change allows bacteria, especially G. vaginalis, to proliferate, producing amines that contribute to a further rise in pH These various bacteria, most of which are commonly found in the vaginas of asymptomatic women, are assumed to be metabolically interdependent. This situation does not lend itself to the application of Koch's postulates to determine a specific cause There is no corresponding disease condition in men, but G. vaginalis is often present in their urethras. the condition may be sexually transmitted, but it also occurs occasionally in women who have never been sexually active The prevalence of vaginosis among women between 14 and 49 years of age is about 30%. Bacterial vaginosis is characterized by a vaginal pH above 4.5 and a copious, frothy vaginal discharge. When tested with a potassium hydroxide solution, these vaginal secretions emit a fishy odor from amines produced by G. vaginalis Diagnosis is based on the vaginal pH, fishy odor (the whiff test), and microscopic observation of clue cells in the discharge. These clue cells are sloughed-off vaginal epithelial cells covered with a biofilm of bacteria, mostly G. vaginalis Treatment is primarily by metronidazole, a drug that eradicates the anaerobes essential to continuation of the disease but allows the normal lactobacilli to repopulate the vagina. Treatments designed to restore the normal population of lactobacilli, such as application of acetic acid gels and even yogurt, have not been shown conclusively to be effective.

Legionellosis

Legionellosis, or Legionnaires' disease, Bc no obvious bacterial cause could be found, eventually identified a previously unknown bacterium, an aerobic gram-negative rod now known as Legionella pneumophila, which is capable of replication within macrophages. Over 44 species of Legionella have now been identified; not all of them cause disease. The disease is characterized by a high fever of 40.5°C, cough, and general symptoms of pneumonia. No perso-to-person transmission seems to be involved bacterium can be readily isolated from natural waters. In addition, the microbes can grow in the water of air-conditioning cooling towers, perhaps indicating that some epidemics in hotels, urban business districts, and hospitals were caused by airborne transmission. The organism has also been found to inhabit the water lines of many hospitals. Most hospitals keep the temperature of hot water lines relatively low (43-55°C) as a safety measure, and in cooler parts of the system this inadvertently maintains a good growth temperature for Legionella This bacterium is considerably more resistant to chlorine than most other bacteria and can survive for long periods in water with a low level of chlorine. Evidence indicates Legionella exist primarily in biofilms that are highly protective. The bacteria are often ingested by waterborne amebae when these are present but continue to proliferate and may even survive within encysted amebae most successful method for water disinfection in hospitals with a need to control Legionella contamination has been installation of copper-silver ionization systems Men over 50 are the most likely to contract legionellosis, especially smokers or the chronically ill. L. pneumophila is also responsible for Pontiac fever, which is essentially another form of legionellosis. Its symptoms include fever, muscular aches, and usually a cough. The condition is mild and self-limiting. During outbreaks of legionellosis, both forms may occur best diagnostic method is culture on a selective charcoal- yeast extract medium. Serological tests to detect O antigen in urine are available. However, these tests detect only one serogroup Azithromycin and other macrolide antibiotics are the drugs of choice for treatment.

Leishmania braziliensis Infection (Mucocutaneous Leishmaniasis)

Leishmania braziliensis infection is known as mucocutaneous leishmaniasis because it affects mucous membranes as well as skin It causes disfiguring destruction of the tissues of the nose, mouth, and upper throat. This form of l often affects workers harvesting the chicle sap used for making chewing gum. This disease is often referred to as American leishmaniasis Diagnosis of cutaneous and mucocutaneous leishmaniasis in the areas where they are endemic usually depends on clinical appearance and microscopic examination of the lesion scrapings Mild cases of cutaneous and mucocutaneous disease will often eventually heal without treatment.

Leishmania tropica Infection (Cutaneous Leishmaniasis)

Leishmania tropica and L. major infection causes a cutaneous form of leishmaniasis sometimes called oriental sore papule appears at the bite site after a few weeks of incubation, ulcerates leaves a prominent scar.

Leptospirosis

Leptospirosis is primarily a disease of domestic or wild animals, but it can be passed to humans and sometimes causes severe kidney or liver disease. The causative agent is the spirochete Leptospira interrogans Leptospira has a characteristic shape: an exceedingly fine spiral, only about 0.1 μm in diameter, wound so tightly that it is barely discernible under a darkfield microscope, stains poorly and is difficult to see under a normal light microscope obligate aerobe that can be grown in a variety of artificial media supplemented with rabbit serum. shed the bacteria in their urine for extended periods. In rats, the bacteria inhabit renal tubules, an immunologically privileged site, where they continue to reproduce and are shed, copiously, in urine for months most common zoonosis; it's endemic in temperate and tropical environments. Humans become infected by contact with urine-contaminated water from freshwater lakes or streams, soil, or sometimes with animal tissue Usually the pathogen enters through minor abrasions in the skin or mucous membranes. When ingested, it enters through the mucosa of the upper digestive system incubation period of 1 to 2 weeks, headaches, muscular aches, chills, and fever abruptly appear. Several days later, the acute symptoms disappear, and the temperature returns to normal. A few days later, however, a second episode of fever may occur Leptospires are observed within nonphagocytic cells of infected patients. It's uncertain how the pathogens enter host cells, but they use this as a mechanism to spread to target organs and evade the immune system. Bc of this, the immune response is delayed long enough (1 or 2 weeks) for the population in the blood and tissues to reach enormous numbers In a small number of cases the kidneys and liver become seriously infected (Weil's disease); kidney failure is the most common cause of death An emerging form of leptospirosis, pulmonary hemorrhagic syndrome, has appeared globally. Affecting the lungs with massive bleeding, it has a fatality rate of more than 50%. Recovery results in a solid immunity, but only to the particular serovar involved. bc the clinical symptoms are not distinctive, many cases are probably never diagnosed. Fifty percent of the 100-200 annual cases in the United States occur in Hawaii. Most cases of leptospirosis are diagnosed by a serological test that is complicated and usually done by central laboratories. However, a number of rapid serological tests are available for a preliminary diagnosis. Also, a diagnosis can be made by sampling blood, urine, or other fluids for the organism or its DNA. Doxycyline (a tetracycline) is the recommended antibiotic for treatment; however, administration of antibiotics in later stages is often unsatisfactory. That immune reactions are responsible for pathogenesis in later stages may be an explanation.

Acute Hepatitis B

Many cases of acute hepatitis B are subclinical; the infected person is often entirely unaware. In about a third of the cases, the patient exhibits symptoms of disease— the person feels unwell and often suffers from low-grade fever; nausea, and abdominal pain. Eventually, jaundice, dark urine, and other evidence of liver damage appears. A long period of gradual recovery marked by fatigue and malaise follows as the damaged liver recovers. However, in a few cases (less than 1%), the patient develops fulminant hepatitis, causing sudden, massive liver damage; survival without a liver transplant is uncommon. If a case of hepatitis persists for more than 6 months, the condition is considered to have become chronic

Lyme Disease (Lyme Borreliosis)

Lyme disease is now the most common vector-borne disease in the United States The seasonal occurrence (summer months), lack of contagiousness among family members, and descriptions of an unusual skin rash that appeared several weeks before the first symptoms suggested a tickborne disease spirochete named Borrelia burgdorferi identified as the cause. In 2016, another causative bacterium, B. mayonii was discovered. In 2013, B. miyamotoi was discovered in the northeastern United States, It causes a similar disease without the rash Tens of thousands of cases are reported annually. In the United States, Lyme disease is most prevalent on the Atlantic coast Field mice are the most important animal reservoir. The nymphal stage of the tick feeds on infected mice and is the most likely to infect humans, even though adult ticks are about twice as likely to carry the bacterial pathogen. This is because nymphal ticks are small and less likely to be noticed before the infection is transmitted Deer are important in maintaining the disease because the ticks feed and mate on them. They are a dead-end host and do not become infected. the ability of the spirochete to remain viable in the disease-tolerant field mice is crucial to maintaining the disease in the wild On humans, the ticks usually attach from a perch on shrubs or grass. They do not feed for about 24 hours, and it usually requires 2 or 3 days of attachment before transfer of bacteria and infection occur. Probably only about 1% of tick bites result in Lyme disease On the Pacific coast, the tick that transmits Lyme disease is the western black-legged tick Ixodes pacificus In the rest of the country, Ixodes scapularis is most often responsible. This latter tick is so small that it is often missed. On the Atlantic coast, almost all Ixodes ticks carry the spirochete; on the Pacific coast, few are infected because that tick feeds on lizards that do not carry the spirochete effectively The first symptom of Lyme disease is usually a rash that appears at the bite site. It is a red area that clears in the center as it expands to a final diameter of about 15 cm, This distinctive rash occurs in about 75% of cases Flulike symptoms appear in a couple of weeks as the rash fades Antibiotics taken during this interval are very effective in limiting the disease. During a second phase, in the absence of effective treatment, there is often evidence that the heart is affected The heartbeat may become so irregular that a pacemaker is required. Incapacitating, chronic neurological symptoms, such as facial paralysis, oppressive fatigue, and memory loss may be present. Some cases result in meningitis and encephalitis In a third phase, months or years later, some patients develop arthritis that may affect them for years. Immune responses to the presence of the bacteria are probably the cause of this joint damage\ Serological tests are challenging to interpret, and following a positive initial ELISA or indirect fluorescent-antibody (FA) test confirmation should be attempted with a Western blot test Also, after effective antibiotic treatment eliminates the bacteria, antibodies—even IgM antibodies—often persist for years and may confuse later attempts at diagnosis Several antibiotics are effective in treating the disease, although in the later stages, large amounts and very extended administration times may be needed.

common cold

More than one virus is involved in the etiology of the common cold. more than 200 different viruses that are members of several different families of viruses are known to cause colds Identification procedures that require isolation and culturing often fail to identify the cause of a cold. PCR to look for the viral DNA or RNA make culturing unnecessary and frequently turn up previously unknown cold viruses Most cold viruses are rhinoviruses (30-50%); coronaviruses (10-15%) are also important. However, 20-30% of viruses that cause colds are classified by researchers as previously unknown Immunity is based on the ratio of IgA antibodies to single serotypes and has a good short-term effectiveness include sneezing, excessive nasal secretion, and congestion easily spread from the throat to the sinuses, the lower respiratory system, and the middle ear, leading to complications of laryngitis and otitis media The uncomplicated cold usually is not accompanied by fever. It is in the interest of a cold-causing virus not to make the cold sufferer too ill—the host needs to move around, shedding the virus to others, especially in mucus Rhinoviruses thrive at a temperature slightly below that of normal body temperature, such as might be found in the upper respiratory system, which is open to the outside environment. No one knows exactly why the number of colds seems to increase with colder weather in temperate zones A single rhinovirus deposited on the nasal mucosa is often sufficient to cause a cold. However, there is surprisingly little agreement on how the cold virus is transmitted to a site in the nose viruses tend to be carried on airborne droplets of water vapor. In the dry air (low humidity) typical of low temperatures, the droplets are smaller and remain airborne longer, facilitating person-to-person transmission At the same time, the cooler air causes the cilia of the ciliary escalator to work more slowly, allowing inhaled viruses to spread in the upper respiratory system. Research has shown that during the first 3 days of a cold, nasal mucus contains a high concentration of cold viruses that multiply in nasal cells. (If mucus is green, the reason is that it contains many white blood cells with iron-containing components directed at destroying pathogens.) The viruses in mucus remain viable on surfaces touched by contaminated fingers for at least several hours the virus is most likely transmitted through finger contact with the nostrils and eyes (tear ducts communicate with the nose) Transmission also occurs when the cold viruses in airborne droplets from coughing and sneezing land on suitable tissues in the nose and eyes

leprosy

Mycobacterium leprae was considered to be the only bacterium that grows in the peripheral nervous system Hansen's disease is the more formal name for leprosy; it is sometimes used to avoid the dreaded name. optimum growth temperature of 30°C and show a preference for the outer, cooler portions of the human body. They survive ingestion by macrophages and eventually invade cells of the myelin sheath of the peripheral nervous system, where their presence causes nerve damage from a cell-mediated immune response M. leprae has a very long generation time, about 12 days. M. leprae and M. lepromatosis have never been grown on artificial media. Armadillos have been found to be a useful way to culture the leprosy bacillus; they have a body temperature of 30-35°C and are often infected in the wild Leprosy occurs in two main forms that reflect the effectiveness of the host's cell-mediated immune system

Treatment of Rabies

Once the symptoms of rabies appear, there is very little in the way of effective treatment—only a handful of survivors have been reported Most of these survivors had received PEP before the appearance of symptoms. There have been only a couple of cases of survival of a patient who had not received PEP The primary treatment, which succeeds in a minority of cases, is to induce an extended coma to minimize excitability while administering antiviral drugs This procedure was first used in the case of a Wisconsin girl bitten by a rabid cat and has come to be called the Milwaukee protocol.

gonorrhea

One of the most common reportable, or notifiable, communicable diseases in the United States is gonorrhea caused by the gram-negative diplococcus Neisseria gonorrhoeae true number of cases is probably much larger, probably two or three times those reported More than 60% of patients with gonorrhea are aged 15 to 24 To infect, the gonococcus must attach to the mucosal cells of the epithelial wall by means of fimbriae. The pathogen nvades the spaces separating columnar epithelial cells, which are found in the oral-pharyngeal area, the eyes, rectum, urethra, opening of the cervix, and the external genitals of prepubertal females invasion sets up an inflammation and, when leukocytes move into the inflamed area, the characteristic pus forms In men, a single unprotected exposure results in infection with gonorrhea 20-35% of the time. Women become infected 60-90% of the time from a single exposure Men become aware of a gonorrheal infection by painful urination and a discharge of pus-containing material from the urethra; About 80% of infected men show these obvious symptoms after an incubation period of only a few days; most others show symptoms in less than a week A common complication is urethritis, although this is more likely to be the result of coinfection with Chlamydia An uncommon complication is epididymitis, an infection of the epididymis. Usually only unilateral, this is a painful condition resulting from the infection ascending along the urethra and the ductus deferens In women, the disease is more insidious. Only the cervix, which contains columnar epithelial cells, is infected. The vaginal walls are composed of stratified squamous epithelial cells, which are not colonized. Very few women are aware of the infection. Later in the course of the disease, there might be abdominal pain from complications such as pelvic inflammatory disease In both men and women, untreated gonorrhea can disseminate and become a serious, systemic infection. Complications of gonorrhea can involve the joints, heart (gonorrheal endocarditis), meninges (gonorrheal meningitis), eyes, pharynx, or other parts of the body Gonorrheal arthritis, which is caused by the growth of the gonococcus in fluids in joints, occurs in about 1% of gonorrhea cases. Joints commonly affected include the wrist, knee, and ankle If a mother is infected with gonorrhea, the eyes of her infant can become infected as it passes through the birth canal. This condition, ophthalmia neonatorum, can result in blindness. Because of the seriousness of this condition and the difficulty of being sure the mother is free of gonorrhea, antibiotics are placed in the eyes of all newborn infants If the mother is known to be infected, an intramuscular injection of antibiotic is also administered to the infant Gonorrheal infections can also be transferred by hand contact from infected sites to the eyes of adults. Gonorrheal infections can be acquired at any point of sexual contact; pharyngeal and anal gonorrhea are not uncommon The symptoms of pharyngeal gonorrhea often resemble those of the usual septic sore throat. Anal gonorrhea can be painful and accompanied by discharges of pus. In most cases, however, the symptoms are limited to itching There is no effective adaptive immunity to gonorrhea. The conventional explanation is that the gonococcus exhibits extraordinary antigenic variability and the gonococcus has certain proteins, Opa proteins that are essential for it to bind to the cells lining the host's urinary and reproductive tracts Recent research has shown that an Opa protein variant binds to a certain receptor (CD66) on CD41 T cells that is needed for activation and proliferation of the cells. This inhibits the development of an immunological memory response against the gonococcus. Almost all clinical isolates of the gonococcus have been found to carry this Opa protein variant suppression of immunity may also explain why people with gonorrhea are more susceptible to other STIs, including HIV Diagnosis of Gonorrhea Gonorrhea in men is diagnosed by finding gonococci in a stained smear of pus from the urethra The typical gramnegative diplococci within the phagocytic leukocytes are readily identified Gram staining of exudates isn't as reliable with women. Usually, a culture is taken from within the cervix and grown on special media. Cultivation of the nutritionally fastidious bacterium requires an atmosphere enriched in carbon dioxide gonococcus is very sensitive to adverse environmental influences (desiccation and temperature) and survives poorly outside the body. It even requires special transporting media to keep it viable for short intervals before the cultivation is under way Cultivation has the advantage of allowing determination of antibiotic sensitivity. Diagnosis of gonorrhea has been aided by the development of an ELISA test that detects N. gonorrhoeae in urethral pus or on cervical swabs within about 3 hours with high accuracy. This and other rapid tests use monoclonal antibodies against antigens on the surface of the gonococcus. Nucleic acid amplification tests (NAATs) are very accurate for identifying clinical isolates from suspected cases.

Chlamydial Pneumonia

Outbreaks of a respiratory illness in populations of college students Chlamydophila pneumoniae, and the disease is known as chlamydial pneumonia resembles mycoplasmal pneumonia transmitted from person to person, probably by the respiratory route Nearly half the U.S. population has antibodies against the organism, an indication that this is a common illness PCR is the preferred diagnostic method bc culturing the bacteria is slow and serological tests don't distinguish species most effective antibiotic is azithromycin

Protozoa in nervous system

Protozoa capable of invading the CNS are rare. However, those that can reach it cause devastating effects.

diagnosis of rabbies

Rabies is usually diagnosed in the laboratory by detection of the viral antigen using the direct fluorescent-antibody (DFA) test, which is nearly 100% sensitive and highly specific These tests can be done on saliva samples, blood, CSF, and skin; postmortem samples are usually taken from the brain For less developed parts of the world, the CDC has developed a rapid immunohistochemical test (RIT). It requires only the use of an ordinary light microscope and has a sensitivity and specificity equivalent to the standard DFA test

lymphogranuloma venereum (LGV)

Several STIs that are uncommon in the United States occur frequently in the tropical areas of the world. For example, Chlamydia trachomatis, the cause of the eye infection trachoma and a major cause of NGU, is also responsible for lymphogranuloma venereum (LGV), a disease found in tropical and subtropical regions caused by serovars of C. trachomatis that are invasive and tend to infect lymphoid tissue invades the lymphatic system, and the regional lymph nodes become enlarged and tender. Suppuration (a discharge of pus) may also occur Inflammation of the lymph nodes results in scarring, which occasionally obstructs the lymph vessels. This blockage sometimes leads to massive enlargement of the external genitals in men. In women, involvement of the lymph nodes in the rectal region leads to narrowing of the rectum. These conditions may eventually require surgery For diagnosis, blood tests for antibodies to the serovars of C. trachomatis causing the disease are satisfactory Direct tests for chlamydia antigens, such as ELISA or NAAT, are available through public health laboratories The drug of choice for treatment is doxycycline.

paralytic (dumb or numb) rabies

Some animals suffer from paralytic (dumb or numb) rabies, in which there is only minimal excitability This form is especially common in cats. The animal remains relatively quiet and even unaware of its surroundings, but it might snap irritably if handled A similar manifestation of rabies occurs in humans and is often misdiagnosed as Guillain-Barré syndrome, a form of paralysis that is usually transient but sometimes fatal, or other neurological conditions.

TORCH Screen Tests

TORCH is a panel of tests that was originally developed to screen mothers for antibodies to microbes that can harm the fetus. TORCH stands for Toxoplasmosis, Other, Rubella, Cytomegalovirus, and Herpes simplex virus. The "Other" category includes many diseases, among which are syphilis, chickenpox, HIV, measles, mumps, and hepatitis B. Since prevention is almost always better than treatment after the fact, women who plan to become pregnant should be up to date on their recommended vaccinations, including those for measles, mumps, and rubella—all of which can cause serious congenital problems

Tuberculosis Vaccines

The BCG vaccine is a live culture of M. bovis that has been made avirulent by long cultivation on artificial media The BCG vaccine has been available since the 1920s and is one of the most widely used vaccines in the world People who have received the vaccine show a positive reaction to tuberculin skin tests. This has always been one argument against its widespread use in the United States is its very uneven effectiveness; fairly effective when given to young children, but for adolescents and adults it sometimes has an effectiveness approaching zero Worse, it has been found that HIV-infected children, who need it most, frequently will develop a fatal infection from the BCG vaccine Recent work indicates that exposure to members of the M. avium-intracellulare complex that is often encountered in the environment may interfere with the effectiveness of the BCG vaccine—which might explain why the vaccine is more effective early in life, before much exposure to such environmental mycobacteria

Paneth cells

The small intestine also contains important antimicrobial defenses, most significantly, millions of specialized, granulefilled cells called Paneth cells. capable of phagocytizing bacteria, and they also produce antibacterial proteins called defensins and the antibacterial enzyme lysozyme.

Latent Period

The symptoms of secondary syphilis will go away with or without treatment, and the disease enters a latent period During this period, there are no symptoms. After 2 to 4 years of latency, the disease is not normally infectious, except for transmission from mother to fetus The majority of cases don't progress beyond the latent stage, even without treatment.

endocarditis

The wall of the heart consists of three layers. The inner layer, called the endocardium, lines the heart muscle itself and covers the valves. An inflammation of the endocardium is called endocarditis.

Prophylaxis and Therapy for Malaria

There are two considerations for antimalarial drugs: for prophylaxis (prevention) or for treatment

unclear relations with EB virus

There is a lengthy list of diseases for which there is a suspected, but not proven, relationship with EB virus. Some of the more familiar of these include multiple sclerosis (autoimmune attack on the nervous system), Hodgkin's lymphoma (tumors of the spleen, lymph nodes, or liver), and nasopharyngeal (nose and pharynx) cancer among certain ethnic groups in southeast Asia and Inuits.

Toxoplasmosis

Toxoplasmosis, a disease of blood and lymphatic vessels, is caused by the protozoan Toxoplasma gondii. a sporeforming protozoan, as is the malarial parasite Cats are an essential part of the life cycle of T. gondii, microbe undergoes its only sexual phase in the intestinal tract. Millions of oocysts are then shed in the cat's feces for 7 to 21 days and contaminate food or water that can be ingested by other animals The oocysts contain sporozoites that invade host cells and form trophozoites called tachyzoites intracellular parasite reproduces rapidly, increased numbers cause the rupture of the host cell and the release of more tachyzoites, resulting in a strong inflammatory response. As the immune system becomes increasingly effective, the disease enters a chronic phase in animals and humans; the infected host cell develops a wall to form a tissue cyst. The numerous parasites within such a cyst reproduce very slowly, if at all, and persist for years, especially in the brain. These cysts are infective when ingested by intermediate or definitive hosts. In people with a healthy immune system, toxoplasmosis infection results in only very mild symptoms or none at all. Approximately 22.5% of the U.S. population, without even being aware of it, have been infected with T. gondii Humans generally acquire the infection by ingesting undercooked meats containing tachyzoites or tissue cysts, although there is a possibility of contracting the disease more directly by contact with cat feces primary danger is congenital infection of a fetus, resulting in stillbirth or a child with severe brain damage or vision problems. This fetal damage occurs only when the initial infection is acquired during pregnancy. T Loss of immune function, AIDS being the best example, allows the inapparent infection to be reactivated from tissue cysts. It often causes severe neurological impairment and may damage vision from the reactivation of tissue cysts in the eye. Toxoplasmosis can be detected by serological tests. usually diagnosed by detecting Toxoplasma-specific IgG and IgM antibodies. IgM antibodies and PCR for Toxoplasma DNA are used to determine a current infection, which is particularly important during pregnancy treated with pyrimethamine in combination with sulfadiazine and folinic acid. This does not, however, affect the chronic bradyzoite stage and is quite toxic

Worldwide Incidence of Tuberculosis

Tuberculosis has emerged as a global pandemic more than 10 million people develop active tuberculosis every year and that infections result in nearly 2 million deaths annually a third of the world's population has latent TB Also, HIV and tuberculosis are almost inseparable, and tuberculosis is the leading direct cause of death in much of the world affected by HIV. TB incidence in the United States steadily decreased for decades The incidence has been approximately three cases per 100,000 people for the past few years, with two-thirds of the cases occurring among foreign born people

Tularemia

Tularemia is an example of a zoonotic disease, that is, a disease transmitted by contact with infected animals, in this case most commonly rabbits and rodents pathogen is Francisella tularensis, a small gram-negative bacillus. It can enter humans by several routes. The most common is penetration of the skin at a minor abrasion, where it creates an ulcer at the site. About a week after infection, the regional lymph nodes enlarge; many will contain pockets of pus The bacterium can multiply in macrophages—as much as a thousand-fold. Mortality is normally less than 3% If left untreated, the proliferation of F. tularensis can lead to sepsis and infection of multiple organs. Almost 90% of cases in the United States are related to contact with rabbits, and the disease is often known locally as rabbit fever. Tularemia is also transmitted in some areas by ticks and deer flies and is known there as deer fly fever. Respiratory infection, usually by dust contaminated by urine or feces of infected animals, can cause an acute pneumonia with a mortality rate exceeding 30%. The infective dose is very small, and handling this organism requires biosafety level 3 procedures At one time, so few cases of tularemia (fewer than 200) were recorded annually in the United States that it was removed from the list of nationally notifiable diseases. However, concern that it might be used as a biological weapon has recently led to its reinstatement on the list The intracellular location of the bacterium is a problem in chemotherapy. Antibiotics such as streptomycin, administered for 10 to 15 days, are an effective treatment.

Viral pneumonia

Viral pneumonia can occur as a complication of influenza, measles, or even chickenpox. A number of Enteroviruses and other viruses have been shown to cause viral pneumonia, but viruses are isolated and identified in fewer than 1% of pneumoniatype infections because few laboratories are equipped to test clinical samples properly for viruse In those cases of pneumonia for which no cause is determined, viral etiology is often assumed if mycoplasmal pneumonia has been ruled out PCR is used to confirm SARS and MERS-CoV

The Influenza Virus

Viruses in the genus Influenzavirus consist of eight separate RNA segments of differing lengths enclosed by an inner layer of protein and an outer lipid bilayer Embedded in the lipid bilayer are numerous projections that characterize the virus. There are two types of projections: hemagglutinin (HA) spikes and neuraminidase (NA) spikes. The HA spikes, of which there are about 500 on each virus, allow the virus to recognize and attach to body cells before infecting them. Antibodies against the influenza virus are directed mainly at these spikes. The term hemagglutinin refers to the agglutination of red blood cells (hemagglutination) that occurs when the viruses are mixed with them. This reaction is important in serological tests. The NA spikes, of which there are about 100 per virus, differ from the HA spikes in appearance and function. They enzymatically help the virus separate from the infected cell as the virus exits after intracellular reproduction. NA spikes also stimulate the formation of antibodies, but these are less important in the body's resistance to the disease than those produced in response to the HA spikes There are three serotypes of human influenza viruses. Influenza A and B viruses cause seasonal epidemics of disease almost every winter in the United States. The emergence of new influenza A viruses can cause an influenza pandemic. Influenza C infections generally cause a mild respiratory illness and are not thought to cause epidemics. Influenza A viruses are identified by variation in the HA and NA antigens. The different forms of the antigens are assigned numbers—for example HI, H2, H3, Nl, and N2. There are 16 subtypes of HA and 9 of NA. Each number change represents a substantial alteration in the protein makeup of the spike. These variations are determined by two processes, antigenic drift and antigenic shift. High mutation rates are a characteristic of RNA viruses, which lack the "proofreading" ability of DNA viruses. Accumulations of these mutations, antigenic drift, eventually allow the virus to elude much host immunity. The virus might still be designated as H2N2, for example, but viral strains arise that reflect minor antigenic changes. So far, the only truly human-adapted viruses are H1N1, H2N2, and H3N2. In an evolutionary sense, from the point of view of the virus it is desirable to accumulate mutations that favor transmission with minimal pathogenicity. (lf the virus quickly kills or makes the host bedridden, it is less likely to be transmitted.) Antigenic shifts mark changes great enough to evade most of the immunity developed in the human population Antigenic shifts involve a major genetic recombination, called reassortment, involving the eight segments of viral RNA virus occurs in avian and mammalian strains; humans generally are not infected by avian strains. However, swine and many wild birds can be infected with both avian and mammalian strains of the influenza virus. Swine are, therefore, good "mixing vessels" in which reassortment occurs

scarlet fever

When the Streptococcus pyogenes strain causing streptococcal pharyngitis produces an erythrogenic (reddening) toxin, the resulting infection is called scarlet fever When the strain produces this toxin, it has been lysogenized by a bacteriophage. this means the genetic information of a bacteriophage (bacterial virus) has been incorporated into the chromosome of the bacterium, so the characteristics of the bacterium have been altered The toxin causes a pinkish red skin rash, which is probably the skin's hypersensitivity reaction to the circulating toxin, and a high fever The tongue has a spotted, strawberry-like appearance and then, as it loses its upper membrane, becomes very red and enlarged Classically, scarlet fever has been considered to be associated with streptococcal pharyngitis, but it might accompany a streptococcal skin infection It is usually a mild illness, but scarlet fever needs antibiotic treatment to prevent later development of rheumatic fever

dental plaque

a sticky film accumulating on the teeth that is formed by and harbors bacteria; also called tartar biofilm intimately involved in the formation of dental caries, or tooth decay Oral bacteria convert sucrose and other carbohydrates into lactic acid, which in turn attacks the tooth enamel bacterial population of plaque predominantly streptococci and filamentous members of the genus Actinomyces.

pharyngitis

inflammation of the mucous membranes of the throat, or sore throat When the larynx is the site of infection, we suffer from laryngitis, which affects our ability to speak The microbes that cause pharyngitis also can cause inflamed tonsils, or tonsillitis.

Chickenpox (Varicella) and Shingles (Herpes Zoster)

mild disease when contracted, in childhood, mortality rate is very low and is usually from complications such as encephalitis (infection of the brain) or pneumonia. Almost half of such deaths occur in adults. result of an initial infection with a herpesvirus Varicellovirus. The species is varicellazoster or officially, human herpesvirus (HHV-3 The disease is acquired when the virus enters the respiratory system, and the infection localizes in skin cells after about 2 weeks The infected skin is vesicular for 3 to 4 days. During that time, the vesicles fill with pus, rupture, and form a scab before healing. Lesions are mostly confined to the face, throat, and lower back but can also occur on the chest and shoulders If varicella infection occurs during early pregnancy, serious fetal damage may occur in about 2% of cases. Reye's syndrome is an occasional severe complication of chickenpox, influenza, and some other viral diseases. A few days after the initial infection has receded, the patient persistently vomits and exhibits signs of brain dysfunction, such as extreme drowsiness or combative behavior. Coma and death can follow. At one time, the death rate of reported cases approached 90%, but this rate has been declining with improved care and is now 30% or lower when the disease is recognized and treated in time. Reye's syndrome affects children and teenagers almost exclusively The use of aspirin to lower fevers in chickenpox and influenza increases the chances of acquiring Reye's syndrome Like all herpesviruses, a characteristic of HHV-3 is its ability to remain latent within the body. enters the peripheral nerves and moves to a central nerve ganglion where it persists as viral DNA Humoral antibodies cannot penetrate into the nerve cell, and because no viral antigens are expressed on the surface of the nerve cell, cytotoxic T cells are not activated. Therefore, neither arm of the adaptive immune system disturbs the latent virus. Latent HHV-3 is located in the dorsal root ganglion near the spine. Later, perhaps as long as decades later, the virus may be reactivated virions produced by the reactivated DNA move along the peripheral nerves to the cutaneous sensory nerves of the skin, where they cause a new outbreak of the virus in the form of shingles (herpes zoster). Shingles is simply a different expression of the virus that causes chickenpox: different because the patient, having had chickenpox, now has partial immunity to the virus Exposing unvaccinated children to shingles has led to their contracting chickenpox Occasionally, such nerve infections can result in nerve damage that impairs vision or even causes paralysis Severe burning or stinging pain is a frequent symptom; occasionally this persists for months or years, a condition called postherpetic neuralgia antiviral drugs acyclovir, valacyclovir, and famciclovir are approved for treatment of shingles. For immunocompromised patients, in which a mortality rate of 17% is reported, and patients with ocular involvement, treatment with antivirals is mandatory live, attenuated varicella vaccine was licensed in 1995. Since then, cases of the disease have declined steadily. There is evidence that the effectiveness of the vaccine, which is about 97% at outset, declines with time.

pustules

pus-filled sacs such as those seen in acne, or pimples

periodontal disease

a term for a number of conditions characterized by inflammation and degeneration of structures that support the teeth The roots of the tooth are protected by a covering of specialized connective tissue called cementum As the gums recede with age or with overly aggressive brushing, the formation of caries on the cementum becomes more common

exanthem

a widespread rash, usually in children A skin rash that arises from disease conditions is called an exanthem; on mucous membranes, such as the interior of the mouth, such a rash is called an enanthem

vesicles

small, fluid-filled lesions

Hepatitis C

soon constituted almost all transfusiontransmitted hepatitis—as testing eliminated HBV in the blood supply there is a delay of about 70 to 80 days between infection and the appearance of detectable HCV antibodies The presence of HCV in contaminated blood cannot be detected during this interval, and about 1 in 100,000 transfusions can still result in infection Blood-collecting facilities in the United States can now detect HCV-contaminated blood within 25 days of infection. A PCR test can detect viral RNA within 1 to 2 weeks after infection HCV has a single strand of RNA and is enveloped. The virus doesn't kill the infected cell, but it triggers an immune inflammatory response that either clears the infection or slowly destroys the liver capable of rapid genetic variation to evade the immune system. This characteristic, along with the fact that currently HCV is cultured very inefficiently, complicates the search for an effective vaccine. a silent epidemic, killing more people than AIDS in the United States. It is often clinically inapparent—few people have recognizable symptoms until about 20 years have elapsed. Probably as many as a third of individuals infected with HCV clear the virus spontaneously Often, hepatitis C is detected only during some routine testing, such as for insurance or blood donation 85%, progress to chronic hepatitis, a much higher rate than with HBV About 25% of chronically infected patients develop liver cirrhosis or liver cancer. Hepatitis C is probably the major reason for liver transplantation Persons infected with HCV should be immunized against both HAV and HBV (a combination vaccine is now available) because they cannot afford the risk of further liver damage A common source of infection is the sharing of injection equipment among IDUs. At least 80% of this group is infected with HCV in more than one-third of the cases, a mode of transmission cannot be identified Treatment includes a combination of HCV protease and polymerase inhibitors, interferon, and ribavirin. Complete eradication of HCV is attained in many cases.

Staphylococcal Skin Infections

spherical gram-positive bacteria, form irregular clusters like grapes can be divided into those that produce coagulase, an enzyme that coagulates (clots) fibrin in blood, and those that do not Coagulase-negative strains, such as Staphylococcus epidermidis, are very common on the skin, where they may represent 90% of the normal microbiota. They are generally pathogenic only when the skin barrier is broken or is invaded by medical procedures, such as the insertion and removal of catheters into veins. On the surface of the catheter , the bacteria are surrounded by a slime layer of capsular material that protects them from desiccation and disinfectants. This is a primary factor in their importance as a healthcare-associated pathogen. S. aureus is the most pathogenic of the staphylococci It is a permanent resident of the nasal passages of 20% of the population, and an additional 60% carry it there occasionally. It can survive for months on surfaces. forms golden-yellow colonies, this protects against the antimicrobial effects of sunlight S. aureus has about 300,000 more base pairs in its genome—much of it devoted to an impressive array of virulence factors and means of evading host defenses. it's coagulase-positive. This is significant bc there is a high correlation between the bacterium's ability to form coagulase and its production of damaging toxins, several of which facilitate the spread of the organism in tissue, damage tissue, or are lethal to host defenses. some strains can cause sepsis and others produce enterotoxins that affect the GI tract Once S. aureus infects the skin, it stimulates a vigorous inflammatory response, and macrophages and neutrophils are attracted to the site of infection. Most strains secrete a protein that blocks chemotaxis of neutrophils to the infection site, and if the bacterium does encounter phagocytic cells, it often produces toxins that kill them. resistant to opsonization. Other proteins it secretes neutralize the antimicrobial peptide defensins on skin, and its cell wall is lysozyme resistant. sometimes responds as a superantigen but often is able to evade the adaptive immune system entirely All humans possess antibodies against S. aureus, but they do not effectively prevent repeated infections. A more serious hair follicle infection is the furuncle (boil), which is a type of abscess, a localized region of pus surrounded by inflamed tissue. Antibiotics do not penetrate well into abscesses & difficult to treat. Draining pus from the abscess as when the body fails to wall off a furuncle, neighboring tissue can be progressively invaded. The extensive damage is called a carbuncle, a hard, round deep inflammation of tissue under the skin. At this stage of infection, the patient usually exhibits the symptoms of generalized illness with fever Staphylococci are the most important causative organism of impetigo. This is a highly contagious skin infection mostly affecting children 2 to 5 years of age, among whom it is spread by direct contact. Streptococcus pyogenes, a pathogen that we will be discussing shortly, can also cause impetigo, although in fewer cases. Sometimes both Sta. aureus and Str. pyogenes are involved. Nonbullous impetigo is the more common form. The pathogen usually enters through some minor break in the skin.s spread is called autoinoculation. lesions eventually rupture and form lightcolored crusts. Topical antibiotics are sometimes applied, but the lesions generally heal without treatment and without scarring.

The stages of tooth decay

1, A tooth with plaque accumulation in difficult-to-clean areas 2. Decay begins as enamel is attacked by acids formed by bacteria 3. Decay advances through the enamel 4.Decay advances into the dentin 5.Decay enters the pulp and may form abscesses in the tissues surrounding the root.

Nematodes (roundworms)

-unsegmented worms -little sensory -bilateral symmetry -many are parasitic -Pinworms, hookworms, Ascariasis, Whipworm (Trichuris trichiura), Trichinellosis

Pathogenisis of tuberculosis

1-2: If the infection progresses, the host isolates the pathogens in a walled-off lesion called a tubercle (meaning lump or knob), a characteristic that gives the disease its name 3. When the disease is arrested at this point, the lesionsslowly heal, becoming calcified. These show up clearly on X-ray films and are called Ghon's complexes. (Computed tomography [CT] is more sensitive than X rays in detecting lesions of TB.) The bacteria may remain viable for years, in which case the disease is called latent TB. Such individuals are infected with M. tuberculosis but do not have TB. The only sign of TB infection is a positive reaction to the tuberculin skin test or TB blood test. Persons with latent TB infection are not infectious and cannot spread TB infection to others. 4. Macrophages ingest and surround the tubercle bacilli, forming a barrier outer layer 5. If the body's defenses fail at this stage, the tubercle breaks down and releases virulent bacilli into the airways of the lung and then the cardiovascular and lymphatic systems

The sequence of events in a typical outbreak of staphylococcal food poisoning

1. Food containing protein is cooked (bacteria usually killed) 2. Then food is contaminated by worker with staphylococci on hands (competing bacteria have been eliminated) 3. Food is left at room temperature. Organisms incubate in food (temperature abuse) long enough to form and release toxins. (Reheating will eliminate staphylococci but not the toxins.) 4. Food containing toxins is eaten 5. In 1-6 hours, staphylococcal intoxication occurs

Salmonellosis steps

1. Salmonella enters an epithelial cell in intestines 2. Salmonella multiplies within a vesicle inside the cell 3. Salmonella multiplies in mucosal cells; there the inflammatory response results in diarrhea. Occasionally, the bacteria cross the epithelial cell membrane and enter the lymphatic system and bloodstream

The stages of periodontal disease

1. Teeth firmly anchored by healthy bone and gum tissue (gingiva) 2. Toxins in plaque irritate gums, causing gingivitis 3. Periodontal pockets form as the tooth separates from the gingiva 4. Gingivitis progresses to periodontitis. Toxins destroy the gingiva and bone that support the tooth and the cementum that protects the root.

pathogenesis of tuberculosis

1. Tubercle bacilli that reach the alveoli of the lung are ingested by macrophages, but often some survive. Infection is present, but no symptoms of disease. 2. Tubercle bacilli multiplying in macrophages cause a chemotactic response that brings additional macrophages and other defensive cells to the area. These form a surrounding layer and, in turn, an early tubercle. Most of the surrounding macrophages are not successful in destroying bacteria but release enzymes and cytokines that cause a lungdamaging inflammation. 3. After a few weeks, disease symptoms appear as many of the macrophages die, releasing tubercle bacilli and forming a caseous center in the tubercle. The aerobic tubercle bacilli do not grow well in this location. However, many remain dormant (latent TB) and serve as a basis for later reactivation of the disease. The disease may be arrested at this stage, and the lesions become calcified 4. In some individuals, disease symptoms appear as a mature tubercle is formed. The disease progresses as the caseous center enlarges in the process called liquefaction. The caseous center now enlarges and forms an air-filled tuberculous cavity in which the aerobic bacilli multiply outside the macrophages 5. Liquefaction continues until the tubercle ruptures, allowing bacilli to spill into a bronchiole and thus be disseminated throughout the lung and then to the circulatory and lymphatic systems.

bovine spongiform encephalopathy (BSE)

A TSE that is much in the news is bovine spongiform encephalopathy (BSE). The disease is better known as mad cow disease because of the behavior of the animals There are no tests to detect PrPSc in live animals. A Western blot test is used to identify PrPSc in postmortem brain tissue in attempts to prevent introduction of BSE into the United States, there are rules prohibiting the use of meat from "downer" animals (fallen and unable to rise and walk) for any purpose and the use of animal protein as a feed supplement. The FDA has banned for human and pet consumption certain portions of the cattle carcass that are most likely to contain a neurological pathogen. Only a small percentage of animal carcasses in the United States are tested for BSE—in Europe and Japan, practically all slaughtered animals are tested If this disease were to establish itself in domestic cattle in the United States, it would be economically devastating. CJD rarely occurs in this age group(young people), and a connection with BSE was feared. Investigation also showed that this variant of CJD (vCJD) differed in significant ways from classic CJD (Table 22.1). A few hundred cases have been identified so far. Considering the long incubation times of prion diseases and that an estimated 1 million cattle had been infected with BSE, it was feared that large numbers of vCJD cases might eventually appear However, this concern has subsided, especially since the number of cases declined from a small peak in 2000 and after it was shown that the affected patients shared a certain limited genetic profile.

Diagnosis and Treatment of the Most Common Types of Bacterial Meningitis

A diagnosis of bacterial meningitis requires a sample of cerebrospinal fluid obtained by a spinal tap, or lumbar puncture A simple Gram stain is often useful; it will frequently determine the identity of the pathogen with considerable reliability Cultures are also made from the fluid. For this purpose, prompt and careful handling is required because many of the likely pathogens are very sensitive and won't survive much storage time or even changes in temperature most frequently used type of serological tests performed on CSF are latex agglutination tests. a negative result doesn't eliminate the possibility of less common bacterial pathogens or nonbacterial causes Bacterial meningitis is life-threatening and develops rapidly. Therefore, prompt treatment of any type of bacterial meningitis is essential, and chemotherapy of suspected cases is usually initiated before identification of the pathogen is complete Broad-spectrum third-generation cephalosporins are usually the first choice of antibiotics; some experts recommend including vancomycin. As soon as identification is confirmed, or perhaps when antibiotic sensitivity has been determined from cultures, the antibiotic treatment may be changed. Antibiotics are also valuable in protecting patient contacts against the spread of an outbreak

genital herpes

A much publicized STI is genital herpes, usually caused by herpes simplex virus type 2 (HSV-2). Herpes simplex virus type 1 (HSV-1) is primarily responsible for oral cold sores, but it can also cause genital herpes There has been a marked increase in genital HSV-1 infections, which is usually acquired by oral-genital contact, and this now constitutes about half of cases of genital herpes in this country Genital herpes lesions appear after an incubation period of up to 1 week and cause a burning sensation. After this, vesicles appear In both men and women, urination can be painful, and walking is quite uncomfortable; the patient is even irritated by clothing. Usually, the vesicles heal in a couple of weeks. The vesicles contain infectious fluid, but many times the disease is transmitted when no lesions or symptoms are apparent. Semen may contain the virus Condoms may not provide protection because in women the vesicles are usually on the external genitals (seldom on the cervix or within the vagina), and in men the vesicles may be on the base of the penis One of the most distressing characteristics of genital herpes is the possibility of recurrences the virus enters a lifelong latent state in nerve cells. Some people have several recurrences a year; for others, recurrence is rare Men are more likely to experience recurrences than women. Reactivation appears to be triggered by factors that lower the immune system, including menstruation, emotional stress or illness (a factor that is also involved in the appearance of cold sores), and being "run down." About 90% of patients with HSV-2 and about 50% of those with HSV-1 will have recurrences. Recurrence rates decrease over time, regardless of treatment. Low numbers of viruses may be produced at any time during latency; thus, the virus is transmitted even in the absence of visible symptoms Diagnosis of genital herpes can be done by culture of the virus taken from a vesicle; however, PCR testing of such samples has proven more sensitive and is potentially faster If there are no lesions to be sampled, serological testing can identify HSV infections or confirm clinical diagnosis by symptoms. There is no cure for genital herpes, although research on its prevention and treatment is intensive Currently, the antiviral drugs acyclovir, famciclovir, and valacyclovir are recommended for treatment. They are fairly effective in alleviating the symptoms of a primary outbreak; there is some relief of pain and slightly faster healing. Taken over several months, they lower the chances of recurrence during that time

gastrointestinal anthrax

A relatively rare form of anthrax is gastrointestinal anthrax caused by ingestion of undercooked food containing anthrax endospores. Symptoms are nausea, abdominal pain, and bloody diarrhea. Ulcerative lesions occur in the gastrointestinal tract ranging from the mouth and throat to, mainly, the intestines. Mortality is usually more than 50%

Trachoma

A serious eye infection, and probably the greatest single cause of blindness by an infectious disease, is trachoma caused by certain serotypes of Chlamydia trachomatis, but not the same ones that cause genital infections In the arid parts of Africa and Asia, almost all children are infected early in their lives The disease is a conjunctivitis transmitted largely by hand contact or by sharing such personal objects as towels. Flies may also carry the bacteria Repeated infections cause inflammation, leading to trichiasis, an in-turning of the eyelashes Abrasion of the cornea, especially by the eyelashes, eventually causes scarring of the cornea and blindness Trichiasis can be corrected surgically, a procedure shown in ancient Egyptian papyri. Secondary infections by other bacterial pathogens are also a factor in the disease Antibiotics to eliminate chlamydia, especially oral azithromycin, are useful in treatment. The disease can be controlled through sanitary practices and health education

human granulocytic anaplasmosis (HGA)

A similar tickborne disease, human granulocytic anaplasmosis (HGA), was formerly called human granulocytic ehrlichiosis. The change occurred when the causative organism, an obligate intracellular bacterium formerly grouped with the ehrlichia, was renamed Anaplasma phagocytophilum The tick vector is Ixodes scapularis, the same species of vector as Lyme disease and babesiosis The symptoms of these diseases are identical, and HGA was identified only when a case occurred in Wisconsin, where the Lone Star tick was unknown. Patients suffer from a flulike disease with high fever and headache; the fatality rate is less than 5%. The diseases probably occur with a frequency much higher than reported Cases of HME and HGA are both widespread and sometimes geographically overlap. Once either disease is suspected (often from detection of morulae in blood smears), diagnosis is usually by the indirect FA test for HME and a polymerase chain reaction (PCR) test for HGA Therapy with antibiotics such as doxycycline is usually effective

AIDS (HIV infection)

AIDS, or HIV infection, is a viral disease that is frequently transmitted by sexual contact its pathogenicity is based on damage to the immune system the lesions resulting from many of the diseases of bacterial and viral origin facilitate the transmission of HIV

Viral Gastroenteritis

Acute gastroenteritis is one of the most common diseases of humans 90% of cases of acute viral gastroenteritis are caused by either the Rotavirus or Norovirus.

infection of lower digestive system

An infection occurs when a pathogen enters the GI tract and multiplies. Microorganisms can penetrate into the intestinal mucosa and grow there, or they can pass through to other systemic organs M (microfold) cells translocate antigens and microorganisms to the other side of the epithelium where they can contact lymphoid tissues (Peyer's patches) to initiate an immune response Infections of the GI tract are characterized by a delay in the appearance of gastrointestinal disturbance while the pathogen increases in numbers or affects invaded tissue usually a fever, one of the body's general responses to an infective organism The general term gastroenteritis is applied to diseases causing inflammation of the stomach and intestinal mucosa Botulism is a special case of intoxication because the ingestion of the preformed toxin affects the nervous system rather than the GI tract

Animal Bites

Animal bites can result in serious infections. About 4.4 million animal bites occur in the United States annually, accounting for about 1% of visits to the emergency rooms in hospitals. Dog bites make up at least 80% of reported bite incidents; cat bites, only about 10%. Cat bites are more penetrating, resulting in a higher infection rate (30-50%) than the bites of dogs (15-20%). Domestic animals often harbor Pasteurella multocida a gramnegative rod similar to the Yersinia bacterium that causes plague P. multocida is primarily a pathogen of animals, and it causes sepsis (hence the name multocida, meaning many-killing). Humans infected have varied responses. For example, local infections with severe swelling and pain can develop at the site of the wound. Forms of pneumonia and sepsis may develop and are life-threatening. Penicillin and tetracycline are usually effective in treating these infections. In addition to P. multocida, an assortment of anaerobic bacterial species are often found in infected animal bites, as well as species of Staphylococcus, Streptococcus, and Corynebacterium. Bites by humans, mostly as a result of fighting, are also prone to serious infections. In fact, before antibiotic therapy became available, nearly 20% of victims of human bites on extremities required amputation—currently only about 5% of cases require it.

furious (classic) rabies

Animals with furious (classic) rabies are at first restless, then become highly excitable and snap at anything within reach. The biting behavior is essential to maintaining the virus in the animal population. Humans also exhibit similar symptoms of rabies, even biting others. When paralysis sets in, the flow of saliva increases as swallowing becomes difficult, and nervous control is progressively lost. The disease is almost always fatal within a few days

diphtheria

Another bacterial infection of the upper respiratory system is diphtheria disease begins with a sore throat and fever, followed by general malaise and swelling of the neck. Corynebacterium diphtheriae, a gram-positive, non-endospore-forming rod. Its morphology is pleomorphic, frequently club-shaped, and it stains unevenly relatively nonvirulent strains are found in the throats of many symptomless carriers bacterium is well suited to droplet transmission and is very resistant to drying tough grayish membrane that forms in the throat in response to the infection is characteristic of diphtheria It contains fibrin, dead tissue, and bacterial cells and can totally block the passage of air to the lungs bacteria don't invade tissues, those that have been lysogenized by a phage can produce a powerful exotoxin, which then circulates in the bloodstream and interferes with protein synthesis Only 0.01 mg of this highly virulent toxin can be fatal. if antitoxin therapy is to be effective, it must be administered before the toxin enters the tissue cells. When such organs as the heart and kidneys are affected by the toxin, the disease can rapidly be fatal. In other cases the nerves can be involved, and partial paralysis results The number of diphtheria cases reported in the United States each year is currently five or fewer. The disease occurs mainly in unvaccinated children and travelers to developing countries A booster dose of vaccine should be administered every 10 years to maintain protective antibody levels. In the United States, when any trauma in adults requires tetanus toxoid, it is usually combined with diphtheria toxoid (Td vaccine) In the past, diphtheria was spread mainly to healthy carriers by droplet infection. Respiratory cases have been known to arise from contact with cutaneous diphtheria Laboratory diagnosis by bacterial identification is difficult, requiring several selective and differential media. Identification is complicated by the need to differentiate toxin-forming isolates from strains that are not toxigenic; both may be found in the same patient. Even though antibiotics such as erythromycin and penicillin control the growth of the bacteria, they do not neutralize the diphtheria toxin. Thus antibiotics should be used only in conjunction with antitoxin.

coccidioidomycosis

Another fungal pulmonary disease, also rather restricted geographically, is coccidioidomycosis Coccidioides immitis, a dimorphic fungus. The arthroconidia are found in dry, alkaline soils of the American Southwest and in similar soils of South America and northern Mexico In tissues, the organism forms a thick-walled body called a spherule filled with endospores in soil, it forms filaments that reproduce by the formation of arthroconidia. The wind carries the arthroconidia to transmit the infection Arthroconidia are often so abundant that simply driving through an endemic area can result in infection, especially during a dust storm Most infections are not apparent, and almost all patients recover in a few weeks, even without treatment. The symptoms of coccidioidomycosis include chest pain and perhaps fever, coughing, and weight loss In less than 1% of cases, a progressive disease resembling tuberculosis disseminates throughout the body. A substantial proportion of adults who are long-time residents of areas where the disease is endemic have evidence of prior infection with C. immitis by the skin test Outbreaks may occur after an earthquake or other event that disturbs large amounts of soil. About 50 to 100 deaths occur annually from this disease in the United States Diagnosis is most reliably made by identifying the spherules in tissue or fluids. The organism can be cultured from fluids or lesions, but laboratory workers must use great care because of the possibility of infectious aerosols Several serological tests and DNA probes are available for identifying isolates. A tuberculin-like skin test is used in screening Fluconazole or itraconazole is used to treat coccidioidomycosis.

chikungunya

Another tropical disease now causing concern is chikungunya symptoms are a high fever and severe, crippling joint pains— especially in the wrists, fingers, and ankles—that can persist for weeks or months, often a rash and even massive blisters The death rate is very low The virus (CHIKV) is transmitted by the Aedes mosquito, primarily Aedes aegypti, which spreads the disease widely in Asia and Africa Recent outbreaks have also been caused by A. albopictus. mutation in CHIKV, which is related to the virus causing western equine encephalitis (WEE) and eastern equine encephalitis (EEE), has adapted the virus to multiply in this insect Chik is the most common disease acquired by travelers, and its local transmission demonstrates how modern air travel contributes to disease emergence A. albopictus is also known as the Asian tiger mosquito because of its bright white stripes. Well adapted to urban settlements, it also survives cold climates and will probably become established eventually even in the northern parts of the United States and the coastal areas of Scandinavia. Because it is an extremely aggressive daytime biter, it is a serious nuisance for outdoor activities. Of greater concern to health officials is that A. albopictus is known, so far, to transmit both chikungunya and dengue, a disease that will be discussed shortly

Noncholera Vibrios

At least 11 species of Vibrio, in addition to V. cholerae, can cause human illness. Most are adapted to life in salty coastal waters. Vibrio parahaemolyticus is found in saltwater estuaries in many parts of the world morphologically similar to V. cholerae and the most common cause of gastroenteritis by Vibrio spp. in humans noncholera Vibrio bacteria cause about 80,000 illnesses and 100 deaths in the United States every year Raw oysters and crustaceans, such as shrimp and crabs, have been associated with several outbreaks of gastroenteritis in the United States in recent years. These infections are life threatening and require early antibiotic therapy for successful treatment.

Bacillus cereus

Bacillus cereus (SEER-eˉ-us) is a large, gram-positive, endosporeforming bacterium that is very common in soil and vegetation and is generally considered harmless. It has, however, been identified as the cause of outbreaks of foodborne illness. Heating the food does not always kill the spores, which germinate as the food cools. Because competing microbes have been eliminated in the cooked food, B. cereus grows rapidly and produces toxins. Rice dishes served in Asian restaurants seem especially susceptible. There are two different clinical syndromes associated with B. cereus gastroenteritis, which correspond to two different toxins elaborated by the bacteria. Some cases of Bacillus cereus gastroenteritis resemble C. perfringens intoxications and are almost entirely diarrheal in nature (usually appearing 8 to 16 hours after ingestion). Other episodes resemble staphylococcal food poisoning, with nausea and vomiting 2 to 5 hours after ingestion. It's suspected that different toxins are involved in producing the differing symptoms. Both forms of the disease are self-limiting. The diseases can be differentiated by isolating at least 105 B. cereus per gram of suspected food.

Shigellosis (Bacillary Dysentery)

Bacterial infections, such as salmonellosis and shigellosis, usually have longer incubation periods (12 hours to 2 weeks) than bacterial intoxications Bacterial infections are often characterized by some fever, indicating the host's response to the infection. Shigellosis, also known as bacillary dysentery to differentiate it from amebic dysentery, is a severe form of diarrhea caused by a group of facultatively anaerobic gramnegative rods of the genus Shigella, don't have any natural reservoir in animals and spread only from person to person There are four species of pathogenic Shigella: S. sonnei, S. dysenteriae, S. flexneri, and S. boydii These bacteria are residents only of the intestinal tract of humans, apes, and monkeys. They are closely related to the pathogenic E. coli The most common species in the United States is S. sonnei; causes mild dysentery. Many cases of so-called traveler's diarrhea might be mild forms of shigellosis infection with S. dysenteriae often results in a severe dysentery and prostration. The toxin responsible is unusually virulent and is known as the Shiga toxin. The infectious dose required to cause disease is small; the bacteria are not much affected by stomach acidity. They proliferate to immense numbers in the small intestine, but the primary site of disease is the large intestine. There, the bacteria attach to epithelial M cells. Membranous cellular ruffles surrounding the cell take the bacterium into the cell, similar to invasion by Salmonella. The bacteria multiply in the cell and soon spread to neighboring cells, producing Shiga toxin that destroys tissue Dysentery is the result of damage to the intestinal wall. Shigellosis can cause as many as 20 bowel movements in one day. Additional symptoms of infection are abdominal cramps and fever. Shigella bacteria rarely invade the bloodstream. Macrophages not only fail to kill Shigella bacteria that they phagocytize, but also are killed by them Diagnosis is usually based on recovery of the microbes from rectal swabs Some immunity seems to result from recovery, but a satisfactory vaccine has not yet been developed. In severe cases of shigellosis, antibiotic-sensitivity testing is necessary to determine appropriate antibiotic treatment.

Tertiary Stage Syphilis

Because the symptoms of primary and secondary syphilis aren't disabling, people may enter the latent period without having received medical attention. In up to 25% of untreated cases, the disease reappears in a tertiary stage This stage occurs only after an interval of many years from the onset of the latent phase. T. pallidum has an outer layer of lipids that stimulates little effective immune response, especially from cell-destroying complement reactions. It has been described as a "Teflon pathogen." most of the symptoms of tertiary syphilis are probably due to the body's immune reactions (of a cellmediated nature) to surviving spirochetes. can be classified generally by affected tissues or type of lesions Gummatous syphilis is characterized by gummas, which are a form of progressive inflammation that appear as rubbery masses of tissue in various organs (most commonly the skin, mucous membranes, and bones) after about 15 years. There they cause local destruction of these tissues but usually not incapacitation or death Cardiovascular syphilis results most seriously in a weakening of the aorta. In preantibiotic days, it was one of the more common symptoms of syphilis; it is now rare Few, if any, pathogens are found in the lesions of the tertiary stage, and they are not considered very infectious Today, it is rare for cases of syphilis to be allowed to progress to this stage Complications of untreated syphilis involving the eyes or central nervous system can occur during any stage of the disease. ocular syphilis causes blurred vision and permanent blindness Symptoms of neurosyphilis can vary widely. The patient can suffer from personality changes and other signs of dementia (paresis), seizures, loss of coordination of voluntary movement (tabes dorsalis), partial paralysis, loss of ability to use or comprehend speech, loss of sight or hearing, or loss of bowel and bladder control.

Treatment of Syphilis

Benzathine penicillin, a long-acting formulation that remains effective in the body for about 2 weeks, is the usual antibiotic treatment of syphilis. The serum concentrations achieved by this formulation are low, but the spirochete has remained very sensitive to this antibiotic For penicillin-sensitive people, several other antibiotics, such as azithromycin, doxycycline, and tetracycline, have also proven effective

Clostridium difficile-associated diarrhea

Clostridium difficile-associated diarrhea is a disease condition that has appeared in recent decades and has been described as being responsible for more deaths than all other intestinal infections combined. C. difficile is a gram-positive, endosporeforming anaerobe found in the stool of many healthy adults. exotoxins it produces cause a disease that manifests itself in symptoms ranging from a mild case of diarrhea to life-threatening colitis (inflammation of the colon) The colitis can result in ulceration, and possible perforation, of the intestinal wall The disease is usually precipitated by the extended use of antibiotics. The elimination of most competing intestinal bacteria permits rapid proliferation of the toxin-producing C. difficile. It occurs mostly in health care settings such as hospitals and nursing homes. Outbreaks have occurred in daycare centers, and caregivers have been known to acquire it from patients. The mortality rate is highest in elderly patients. C. difficile causes a half-million infections and as many as 29,000 deaths annually infections are treated with vancomycin or fidaxomicin, recurrence is common.

Botulism

Botulism, a form of food poisoning, is caused by Clostridium botulinum, an obligately anaerobic, endospore-forming gram positive rod found in soil and many aquatic sediments Ingesting the endospores usually does no harm, but in anaerobic environments, such as sealed cans, the microorganism produces an exotoxin neurotoxin is highly specific for the synaptic end of the nerve, where it blocks the release of acetylcholine, a chemical necessary for transmitting nerve impulses across synapses undergo a progressive flaccid paralysis for 1 to 10 days and may die from respiratory and cardiac failure. Nausea, but no fever, may precede the neurological symptoms The initial neurological symptoms vary, but nearly all sufferers have double or blurred vision Other symptoms include difficulty swallowing and general weakness Incubation time varies, but symptoms typically appear within a day or two recovery from the disease does not confer immunity because the toxin is usually not present in amounts large enough to be effectively immunogenic. botulinal toxin will be destroyed by most ordinary cooking methods that bring the food to a boil. Nitrites prevent C. botulinum from growing after the endospores germinate Botulinal toxin doesn't form in acidic foods (below pH 4.7). Such acidic foods can therefore be safely preserved without the use of a pressure cooker. There have been cases of botulism from acidic foods that normally would not have supported the growth of the botulism organisms; most of these episodes are related to mold growth, which metabolized enough acid to allow C. botulinum to begin growing

Campylobacter

Campylobacter are gram-negative, microaerophilic, spirally curved bacteria that have emerged as the leading cause of diarrhea in the United States adapt well to the intestinal environment of animal hosts, especially poultry. Culturing Campylobacter requires conditions of low oxygen and high carbon dioxide developed in special apparatus bacteria's optimum growth temperature of about 42°C approximates that of their animal hosts, but the bacteria do not replicate in food Almost all retail chicken is contaminated with Campylobacter. Nearly 60% of cattle excrete the organism in feces and milk, but retail red meats are less likely to be contaminated infectious dose is fewer than 1000 bacteria characterized by fever, cramping abdominal pain, and diarrhea or dysentery. Normally, recovery follows within a week. An unusual complication of campylobacterial infection is that it is linked, in about 1 in 1000 cases, to the neurological disease Guillain-Barré syndrome, a temporary paralysis. Apparently, a surface molecule of the bacteria resembles a lipid component of nervous tissue and provokes an autoimmune attack Campylobacteriosis is prevented by thoroughly cooking chicken and pasteuring milk. Infections may be treated with azithromycin.

Cat-Scratch Disease

Cat-scratch disease, although it receives little attention, is surprisingly common An estimated 22,000 or more cases occur annually in the United States pathogen is an aerobic, gram-negative bacterium, Bartonella henselae Microscopy shows that the bacterium can inhabit the interior of some cat red blood cells. It is connected to the exterior of the cell and to the surrounding extracellular fluid by a pore. Resident there, the bacteria cause a persistent bacteremia in cats; it is estimated that as many as 40% of domestic and feral (wild) cats carry these bacteria in their blood The primary mode of transmission is by the scratch of a cat; it is uncertain whether bites of cats or of cat fleas transmit the disease to humans. But the presence of cat fleas is definitely a requirement for the infection to be maintained among cats. B. henselae multiplies in the digestive system of the cat flea and survives for several days in flea feces. Cat claws then become contaminated from flea feces. initial sign is a papule at the infection site, which appears 3 to 14 days after exposure. Swelling of the lymph nodes and usually malaise and fever follow in a couple of weeks. Cat-scratch disease is ordinarily self-limiting, with a duration of a few weeks, but in severe cases antibiotic therapy may be effective.

Chagas disease (American trypanosomiasis)

Chagas disease, also known as American trypanosomiasis, is a protozoan disease of the cardiovascular system Trypanosoma cruzi, a flagellated protozoan endemic in Central America and parts of South America, where it chronically infects an estimated 8 million and kills as many as 50,000 annually. It has been introduced into the United States by population migration reservoir for T. cruzi is a wide variety of wild animals, including rodents, opossums, and armadillos. The arthropod vector is the reduviid bug, called the "kissing bug" because it often bites people near the lips The bitten human or animal often rubs the feces into the bite wound or other skin abrasions by scratching or into the eye by rubbing. The infection progresses in stages The acute stage, characterized by fever and swollen glands lasting for a few weeks, may not cause alarm. However, 20-30% of people infected will develop a chronic form of the disease—in some cases, 20 years later. Damage to the nerves controlling the peristaltic contractions of the esophagus or colon can prevent them from transporting food. This causes them to become grossly enlarged, conditions known as megaesophagus and megacolon. Most deaths are caused by damage to the heart, which occurs in about 40% of chronic cases. Pregnancy during the chronic stage can result in congenital infections In the acute phase, the trypanosomes can sometimes be detected in blood samples. During the chronic phase these are undetectable—although patients can transmit the infection by transfusions, transplants, and congenitally. Diagnosis of chronic disease depends on serological tests, which are not very sensitive or specific. Two, or even three, repeated samplings may be required. Treating very difficult when chronic, progressive stages have been reached. The trypanosome multiplies intracellularly and is difficult to reach chemotherapeutically The only drugs currently available are nifurtimox and benznidazole, which are triazole derivatives found to eliminate infection in about 60% of infected children and is less toxic than nifurtimox These drugs are effective only during the early, acute phase, when few people realize they are infected, and must be administered for an extended time, 30 to 60 days. Neither drug is effective during the chronic stage; both also have serious side effects.

Dengue and Severe Dengue

Compared to yellow fever, dengue is a similar but milder disease also transmitted by A. aegypti mosquitoes endemic in the Caribbean and other tropical environments Most infections by the dengue virus (DENV) causing dengue are asymptomatic, and the disease itself may vary from a mild case of fever to a severe, fatal disease If the patient suffers from severe bleeding and organ impairment, the case is classified as severe dengue. Severe dengue occurs mostly in patients with their second dengue infection and in infants who have passive immunity from their mother It appears that antibodies to the virus enhance its ability to enter cells, a development called antibody enhancement It does not appear to have an animal reservoir The primary mosquito vector for dengue is common in the Gulf states An efficient secondary vector, Aedes albopictus, has also expanded widely in range in recent years. Attempts to control dengue by vector control have not met with success However, the risk of antibody enhancement and severe dengue is proving difficult to overcome. Effective antiviral drugs have yet to be developed

Cryptosporidiosis

Cryptosporidiosis is caused by the protozoan Cryptosporidium. The most prevalent species affecting humans are C. parvum and C. hominis Infection occurs when humans ingest the cryptosporidian oocysts The oocysts eventually release sporozoites into the small intestine. The motile sporozoites invade the epithelial cells of the intestine and undergo a cycle that eventually releases oocysts to be excreted in the feces The disease is a cholera-like diarrhea lasting 10 to 14 days. In immunodeficient individuals, including AIDS patients, the diarrhea becomes progressively worse and is life-threatening transmitted to humans largely through recreational and drinking water systems contaminated with oocysts of Cryptosporidium, mostly from animal wastes, especially cattle The oocysts, like the cysts of G. intestinalis, are resistant to chlorination and must be removed from water by filtration. Even filtration sometimes fails Alternatives to routine chlorination are ultraviolet radiation, ozonation, and chlorine dioxide An infectious dose may be as low as ten oocysts. Fecal-oral transmission resulting from poor sanitation Most widely used is an FA test that can simultaneously detect both G. intestinalis cysts and Cryptosporidium oocysts Cryptosporidiosis is most reliably diagnosed in the laboratory by detecting oocysts in fecal samples by microscopic examination of acid-fast stains

Cutaneous anthrax

Cutaneous anthrax results from contact with material containing anthrax endospores. Over 90% of naturally occurring cases of anthrax in humans are cutaneous; the endospore enters at some minor skin lesion A papule appears and then eventually vesicles, which rupture and form a depressed, ulcerated area that is covered by a black eschar (scab) (The name anthrax is derived from the Greek word for coal.) In most cases the pathogen does not enter the bloodstream, and other symptoms are limited to a low-grade fever and malaise. However, if the bacteria enter the bloodstream, mortality without antibiotic treatment can reach 20%; with antibiotic therapy, mortality is usually less than 1%

Cystitis

Cystitis is a common inflammation of the urinary bladder in females. Symptoms often include dysuria (difficult, painful, urgent urination) and pyuria female urethra is less than 2 inches long, and microorganisms traverse it readily. It's also closer than the male urethra to the anal opening and its contaminating intestinal bacteria In either gender, most cases are due to infection by E. coli, which can be identified by cultivation on differential media such as MacConkey's agar Another frequent bacterial cause is the coagulase-negative Staphylococcus saprophyticus As a general rule, a urine sample with more than 1,000 colony forming units (CFU) per milliliter of a single species indicates cystitis diagnosis should also include a positive urine test for leukocyte esterase (LE), an enzyme produced by neutrophils—which indicates an active infection. Nitrofurantoin usually clears cases of cystitis quickly. A fluoroquinolone is often successful if drug resistance is encountered.

Diagnosis of Syphilis

Diagnosis of syphilis is complex because each stage of the disease has unique requirements. Tests fall into three general groups: visual microscopic inspection, nontreponemal serological tests, and treponemal serological tests For preliminary screening, laboratories use either nontreponemal serological tests or microscopic examination of exudates from lesions when these are present. If a screening test is positive, the results are confirmed by treponemal serological tests. syphilis because serological tests for this stage are not reliable; antibodies take 1 to 4 weeks to form. The spirochetes can be detected in exudates of lesions by microscopic examination with a darkfield microscope. A darkfield microscope is necessary because the bacteria stain poorly and are only about 0.2 μm in diameter, near the lower limit of resolution for a brightfield microscope. Similarly, a direct fluorescent-antibody test (DFA-TP) using monoclonal antibodies will both show and identify the spirochete At the secondary stage, when the spirochete has invaded almost all body organs, serological tests are reactive. Nontreponemal serological tests are so called because they are nonspecific; they detect reagin-type antibodies, not the antibodies produced against the spirochete itself Reagin-type antibodies are apparently a response to lipid materials the body forms as an indirect reaction to infection by the spirochete. The antigen used in such tests is thus not the syphilis spirochete but an extract of beef heart (cardiolipin) that seems to contain lipids similar to those that stimulated the reagin-type antibody production These tests will detect only about 70-80% of primary syphilis cases, but they will detect 99% of secondary syphilis cases An example of nontreponemal tests is the slide agglutination VDRL test (for Venereal Disease Research Laboratory). Also used are modifications of the rapid plasma reagin (RPR) test, which is similar. newest nontreponemal test is an ELISA test that uses the VDRL antigen. There are also treponemal-type serological tests that react directly with the spirochete. Certain enzyme immunoassay (EIA) treponemal tests can be done in many laboratories and offer high-throughput screening. There are also simple rapid diagnostic tests (RDTs) of this type that can be done from a finger-prick blood sample in a physician's office. Only treponemal-type tests are used for confirmatory testing. An example is the fluorescent treponemal antibody absorption test, or FTA-ABS test, an indirect fluorescentantibody test Treponemal tests are not used for screening because about 1% of the results will be false positives, but a positive test with both treponemal and nontreponemal types is highly specific

Prevention of Malaria

Effective control of malaria is not in sight probably require a combination of vector control and chemotherapeutic and immunological approaches. most promising preventative method is the use of insecticide-treated bed nets, because the Anopheles mosquito is a night feeder In malarial areas, a sleeping room often will contain hundreds of mosquitoes, 1-5% of which are infectious. The expense of these efforts and the need for an effective political organization in malarial areas are probably going to be as important in controlling the disease as are advances in medical research.

Enteroaggregative E. coli (EAEC)

Enteroaggregative E. coli (EAEC) is a group of coliforms found only in humans named for their growth habit, in which the bacteria cause a "stacked-brick" configuration when grown with epithelial cells EAEC are not invasive but produce an enterotoxin causing a watery diarrhea. Some studies suggest that another pathotype, diffusely adherent E. coli, is also associated with diarrheal illness

Enterovirus D68

Enterovirus D68 (EV-D68) causes coldlike symptoms. associated with severe respiratory illness. Small numbers of EV-D68 have been reported regularly since 1987 Children and teenagers are most likely to get infected with EV-D68 and bc ill because they do not yet have immunity from previous exposures to these viruses. Some children may have difficulty breathing, although most people recover within a few days. Symptoms can be relieved by cough suppressants and antihistamines, but these medications do not speed recovery

Relapsing Fever

Except for the species that causes Lyme disease all members of the spirochete genus Borrelia cause relapsing fever In the United States, the disease is transmitted by soft ticks that feed on rodents. The disease occurs mostly in the western states The incidence of relapsing fever increases during the summer months, when the activity of rodents and arthropods increases characterized by fever, sometimes in excess of 40.5°C, jaundice, and rose-colored skin spots. After 3 to 5 days, the fever subsides Three or four relapses may occur, each shorter and less severe than the initial fever. Each recurrence is caused by a different antigenic type of the spirochete, which evades existing immunity Diagnosis is made by observing the bacteria in the patient's blood, which is unusual for a spirochete disease. Tetracycline is effective for treatment

Giardia intestinalis

Giardia intestinalis (also known as G. lamblia and occasionally as G. duodenalis) is a flagellated protozoan that is able to attach firmly to a human's intestinal wall G. intestinalis is the cause of giardiasis, a prolonged diarrheal disease. Sometimes persisting for weeks, giardiasis is characterized by malaise, nausea, flatulence (intestinal gas), weakness, weight loss, and abdominal cramps distinctive odor of hydrogen sulfide can often be detected in the breath or stools. The protozoa sometimes occupy so much of the intestinal wall that they interfere with food absorption About 7% of the population are healthy carriers and shed the cysts in their feces. The pathogen is also shed by a number of wild mammals, especially beavers Most outbreaks are transmitted by contaminated water supplies Bc the cyst stage is relatively insensitive to chlorine, filtration or boiling of water supplies is usually necessary to eliminate the cysts from water. Microscopic examination is often used for diagnosis. Because G. intestinalis isn't reliably excreted, stool samples collected on 3 successive days may be needed serological tests that use antibodies to test for the presence of trophozoites and cysts in feces. Testing of drinking water for Giardia is difficult but often necessary to prevent or trace disease outbreaks. These tests are frequently combined with tests for Cryptosporidium protozoa, discussed in the next section Treatment with metronidazole or quinacrine hydrochloride is usually effective within a week. Nitazoxanide is used to treat both cryptosporidiosis and giardiasis. Like metronidazole, it affects anaerobic metabolic pathways, but it requires a shorter treatment regimen

Periodontitis

Gingivitis can progress to a chronic condition called periodontitis, an insidious condition that generally causes little discomfort About 35% of adults suffer from periodontitis, which is increasing in incidence as more people retain their teeth into old age gums are inflamed and bleed easily. Sometimes pus forms in periodontal pockets surrounding the teeth As the infection continues, it progresses toward the root tips. The bone and tissue that support the teeth are destroyed, eventually leading to loosening and loss of the teeth Numerous bacteria of many different types, primarily Porphyromonas species, are found in these infections; the damage to tissue is done by an inflammatory response to the presence of these bacteria can be treated surgically by eliminating the periodontal pockets Acute necrotizing ulcerative gingivitis, also termed Vincent's disease or trench mouth, is one of the more common serious mouth infections. The disease causes enough pain to make normal chewing difficult. Foul breath (halitosis) also accompanies the infection. the bacteria usually associated with this condition is Prevotella intermedia averaging up to 24% of the isolates. bc pathogens are usually anaerobic, treatment includes hydrogen peroxide after debridement. Antibiotics may be effective

Gram-Positive Sepsis

Gram-positive bacteria are now the most common cause of sepsis. Both staphylococci and streptococci produce potent exotoxins that cause toxic shock syndrome The frequent use of invasive procedures in hospitals allows gram-positive bacteria to enter the bloodstream. Such healthcare-associated infections (HAIs) are a particular risk for patients who undergo regular dialysis for kidney dysfunction The bacterial components that lead to septic shock in gram-positive sepsis are not known with certainty. Possible sources are various fractions of the gram-positive cell wall or even bacterial DNA An especially important group of gram-positive bacteria are the enterococci, which are responsible for many HAIs. The enterococci are inhabitants of the human colon and frequently contaminate skin. Once considered relatively harmless, two species in particular, Enterococcus faecium and Enterococcus faecalis, are now recognized as leading causes of HAIs of wounds and the urinary tract. Enterococci have a natural resistance to penicillin and have rapidly acquired resistance to other antibiotics. What has made them something of a medical emergency is the appearance of vancomycin-resistant strains. Vancomycin was often the only remaining antibiotic to which these bacteria, especially E. faecium, were still sensitive. Among isolates of E. faecium from HAIs of the bloodstream, almost 90% are now resistant. There is an emerging awareness of group B streptococci (GBS). S. agalactiae the only GBS and is the most common cause of life-threatening neonatal sepsis The CDC recommends that pregnant women be tested for vaginal GBS and that women with GBS be offered antibiotics during labor.

three bacterial species that cause meningitis

Haemophilus influenzae type B Haemophilus influenzae type B S. pneumoniae All three possess a capsule that protects them from phagocytosis as they replicate rapidly in the bloodstream, from which they might enter the cerebrospinal fluid gram-negative pathogens or the release of cell wall fragments (peptidoglycans and teichoic acids) from gram-positive bacteria

Helminthic infections in Digestive tract

Helminthic parasites are very common in the human intestinal tract, especially in warm, moist regions where sanitation is poor These diseases are called Neglected Tropical Diseases (NTDs) bc they infect 1.5 billion people in the poorest countries and are not yet controlled even w/ parasites' size and formidable appearance, light infections often produce few symptoms so well adapted to their human hosts, and vice versa, that when their presence is revealed, it is often a surprise

Hepatitis B

Hepatitis B is caused by the hepatitis B virus (HBV). HBV and HAV are completely different viruses: HBV is larger, its genome is double-stranded DNA, and it is enveloped. it's a unique DNA virus; instead of replicating its DNA directly, it passes through an intermediate RNA stage resembling a retrovirus The serum from patients with hepatitis B contains three distinct particles. The largest is the complete virion; it's infectious and capable of replicating. It's often referred to as a Dane particle. There are also smaller spherical particles, about half the size of a complete virion, and filamentous particles, which are tubular particles similar in diameter to the spherical particles but about ten times as long. The spherical and filamentous particles are unassembled components of the virion without nucleic acids; assembly is evidently not very efficient, and large numbers accumulate Fortunately, these numerous unassembled particles contain hepatitis B surface antigen (HBsAg), which can be detected with antibodies to them antibody tests make convenient screening of blood for HBV possible Many chronic carriers eventually die of liver cancer or cirrhosis Infection by HBV can take a varied path. There is a marked difference between acute and chronic HBV infection. If an individual is infected with HBV, acute hepatitis can result. Most such cases will resolve spontaneously as the patient clears the virus. About 5% of cases of acute hepatitis B will progress to chronic hepatitis B

Hepatitis D

Hepatitis D can occur as either acute (coinfection form) or chronic (superinfection form) hepatitis In people with a case of self-limiting acute hepatitis B, coinfection with HDV disappears as the HBV is cleared from the system, and the condition resembles a typical case of acute hepatitis B HBV infection in chronic stage, superinfection with HDV is often accompanied by progressive liver damage and a fatality rate several times that of people infected with HBV alone Hepatitis D is linked to the epidemiology of hepatitis B In the United States and northern Europe, the disease occurs predominantly in high-risk groups, such as IDUs

Hepatitis E (HEV)

Hepatitis E (HEV) is spread by fecal-oral transmission, much like hepatitis A, which it clinically and structurally resembles endemic in areas with poor sanitation, especially India and Southeast Asia. HEV does not cause chronic liver disease, but for some unexplained reason it is responsible for a mortality rate in excess of 20% in pregnant women

Hepatitis

Hepatitis is an inflammation of the liver. At least five different viruses cause hepatitis, and probably more remain to be discovered or become better known. Hepatitis is an occasional result of infections by other viruses such as Epstein-Barr virus (EBV) or cytomegalovirus (CMV). Drug and chemical toxicity can also cause acute hepatitis that is clinically identical to viral hepatitis. The characteristics of the various forms of viral hepatitis are summarized in Diseases in Focus 25.3 on page 743.

Herpes Simplex

Herpes simplex viruses (HSV) can be separated into two identifiable groups, HSV-1 and HSV-2 HSV-1 is transmitted primarily by oral or respiratory routes, and infection usually occurs in infancy. Serological surveys show that about 90% of the U.S. population has been infected. Frequently, this infection is subclinical, but many cases develop lesions known as cold sores or fever blisters. Cold sores, caused by herpesvirus infections, are often confused with canker sores. The cause of canker sores is unknown, but their occurrence is often related to stress or menstruation. While similar to cold sores in appearance, canker sores usually appear in different areas. painful sores on movable mucous membranes, such as those on the tongue, cheeks, and inner surface of the lips. They ordinarily heal in a few days but often recur. HSV-1 usually remains latent in the trigeminal nerve ganglia communicating between the face and the central nervous system Recurrences of HSV-1 infection can be triggered by events such as excessive exposure to ultraviolet radiation from the sun, emotional upsets, or the hormonal changes associated with menstruation. HSV-1 infection can be transmitted by skin contact among wrestlers; this is colorfully termed herpes gladiatorum Nurses, physicians, and dentists are occupationally susceptible to herpetic whitlow, infections of the finger caused by contact with HSV-1 lesions—as are children with herpetic oral ulcers HSV-2, is transmitted primarily by sexual contact. cause of genital herpes, differentiated from HSV-1 by its antigenic makeup and by its effect on cells in cell culture It is latent in the sacral nerve ganglia found near the base of the spine, a different location from that of HSV-1. Very rarely, either type of the herpes simplex virus may spread to the brain, causing herpes encephalitis. Infections by HSV-2 are more serious, with a fatality rate as high as 70% if untreated. Only about 10% of survivors can expect to lead healthy lives. When administered promptly, acyclovir often cures such encephalitis. Even so, the mortality rate in certain outbreaks is still 28%, and only 38% of the survivors escape serious neurological damage

Histoplasmosis

Histoplasmosis superficially resembles tuberculosis lung lesions in many people who were tuberculin-test-negative. Although the lungs are most likely to be initially infected, the pathogens may spread in the blood and lymph, causing lesions in almost all organs of the body Symptoms are usually poorly defined and mostly subclinical, and the disease passes for a minor respiratory infection In a few cases, perhaps fewer than 0.1%, histoplasmosis progresses, and it becomes a severe, generalized disease. This occurs with an unusually heavy inoculum or upon reactivation, when the infected person's immune system is compromised. causative organism, Histoplasma capsulatum is a dimorphic fungus; that is, it has a yeastlike morphology in tissue growth, and, in soil or artificial media, it forms a filamentous mycelium carrying reproductive conidia In the body, the yeastlike form is found intracellularly in macrophages, where it survives and multiplies. the disease is found in the states adjoining the Mississippi and Ohio rivers. More than 75% of the population in some of these states have antibodies against the infection humans acquire the disease from airborne conidia produced under conditions of appropriate moisture and pH levels. These conditions occur especially where droppings from birds and bats have accumulated. Birds themselves, because of their high body temperature, do not carry the disease, but their droppings provide nutrients, particularly a source of nitrogen, for the fungus Bats, which have a lower body temperature than birds, carry the fungus, shed it in their feces, and infect new soil sites. Clinical signs and history, serological tests for Histoplasma antigen and, most important, either isolating the pathogen or identifying it in tissue specimens are necessary for proper diagnosis. most effective chemotherapy is itraconazole.

Hookworms

Hookworm infections were once a very common parasitic disease in the southeastern states In the United States, the species most often seen is Necator americanus. Another species, Ancylostoma duodenale, is widely distributed around the world. hookworm attaches to the intestinal wall and feeds on blood and tissue rather than on partially digested so the presence of large numbers of worms can lead to anemia and lethargic behavior Heavy infections can also lead to a bizarre symptom known as pica. Pica is a symptom of iron deficiency anemia. Bc the life cycle of the hookworm requires human feces to enter the soil and bare skin to contact contaminated soil, the incidence of the disease has declined greatly with improved sanitation and the practice of wearing shoes Hookworm infections are diagnosed by finding parasite eggs in feces can be treated effectively with mebendazole

pyelonephritis

In 25% of untreated cases, cystitis may progress to pyelonephritis, an inflammation of one or both kidneys Symptoms are fever and flank or back pain. In females, it's often a complication of lower urinary tract infections causative agent E. Coli 7n in5% of the cases Pyelonephritis generally results in bacteremia; blood cultures and a Gram stain of the urine for bacteria are useful for diagnosis A urine sample of more than 100,000 CFUs/ml of a single species indicates pyelonephritis If pyelonephritis becomes chronic, scar tissue forms in the kidneys and severely impairs their function Bc pyelonephritis is a potentially life-threatening condition, treatment usually begins with intravenous, extended-term administration of a broadspectrum antibiotic, such as a second- or third-generation cephalosporin

Unidentified agents

In August 2014 and November 2016, the CDC received increased reports of people with acute flaccid myelitis (AFM). Symptoms include limb weakness and one or more of the following: facial droop/weakness, drooping eyelids, and difficulty with swallowing or slurred speech. The 2014 increase coincided with a national outbreak of severe respiratory illness caused by a nonpolio enterovirus called EV-D68. Preliminary studies suggest EV-D68 may be the cause of AFM. Bell's palsy occurs when a nerve that controls facial muscles is inflamed and can't communicate with muscles. This results in symptoms of drooping eyelid or mouth on one side of the face This inflammation may be caused by one of the herpes viruses: HHV-1, HHV-3, HHV-4, and HHV-5 have all been suggested. Acyclovir may shorten the course of the disease. However, most people recover within 6 months with or without treatment. There is no diagnostic test for chronic fatigue syndrome (CFS). It is diagnosed by a persistent, unexplained fatigue that lasts at least 6 months with at least four of these symptoms: sore throat, tender lymph nodes, muscle pain, pain in multiple joints, headaches, unrefreshing sleep, malaise after exercise, and impaired short-term memory or concentration. The condition affects an estimated 800,000 to 2.5 million people in the United States. A number of viruses have been suggested as the cause, but current studies suggest that no one pathogen causes CFS and that the illness may be triggered by a variety of infections

Gingivitis

In many cases of periodontal disease, the infection is restricted to the gums, or gingivae resulting inflammation, called gingivitis, is characterized by bleeding of the gums while the teeth are being brushed condition experienced by at least half of the adult population shown experimentally that gingivitis will appear in a few weeks if brushing is discontinued and plaque is allowed to accumulate An assortment of streptococci, actinomycetes, and anaerobic gram-negative bacteria predominate in these infections

Related Lyssavirus Encephalitis

In recent years, a few fatal cases of encephalitis that are clinically indistinguishable from classic rabies have occurred in Australia and Scotland—countries considered free of rabies Classic rabies is caused by one of 11 known genotypes of the genus Lyssavirus and is widespread worldwide. Other, nonrabies, lyssaviruses causing encephalitis are indigenous to Europe, Australia, Africa, and the Philippines, most commonly in bats. Different species of bats are infected with distinct variants of the rabies-related lyssaviruses

Rat-Bite Fever

In the United States, about 20,000 rat bites occur annually— and a bite may cause the disease rat-bite fever about half of both wild and laboratory rats are known to carry the bacterial pathogens, only a minority of rat bites (about 10%) result in disease. North America the more common disease, called streptobacillary ratbite fever, is caused by Streptobacillus moniliformis (when the pathogen is ingested, the disease is termed Haverhill fever) a filamentous, gram-negative, highly pleomorphic, fastidious bacterium that is difficult to culture, although isolation in culture is the best diagnostic method symptoms are initially fever, chills, and muscle and joint pain, followed in a few days by a rash on the extremities. Occasionally there are more serious complications; if untreated, mortality is around 10%. The other bacterial pathogen causing rat-bite fever is Spirillum minus. In this case, the disease is called spirillar fever; in Asia, where most cases occur, it is known as sodoku. It is more likely to occur in bites by wild rodents. The symptoms are similar to those of streptobacillary rat-bite fever. Because the pathogen cannot be cultured, diagnosis is made by microscopic observation of the gram-negative, spiral-shaped bacterium. Treatment by penicillin is usually effective for both forms of rat-bite feve

Polio Epidemiology and Eradication Efforts

In the epidemiology of the poliovirus, naturally occurring, wild-type (WPV) virus is distinguished from vaccine-derived virus (VDPV). VDPV is an attenuated vaccine virus that has reverted to virulence and is in circulation. The vaccine used was tOPV by 2000 the number of case reports had fallen by 99% the extinction of WPV 2 poliovirus—indicating that eradication might be possible However, persistent reservoirs of WPV remain in Nigeria, Pakistan, and Afghanistan.

Diagnosis of Influenza

Influenza is difficult to diagnose reliably from clinical symptoms, which numerous respiratory diseases share can diagnose influenza A and B within 20 minutes from a sample taken in a physician's office (from nasal washes or nasal swabs) These rapid tests have varying sensitivity and are most useful during influenza season PCR is used to document strains that are circulating

Leishmania donovani Infection (Visceral Leishmaniasis)

Leishmania donovani infection occurs in much of the tropical world, although 90% of the cases occur in India, Ethiopia, Somalia, South Sudan, Sudan, and Brazil Visceral leishmaniasis is often fatal. Early symptoms, following infection by as long as a year, resemble the chills and sweating of malaria As the protozoa proliferate in the liver and spleen, these organs enlarge greatly. Eventually, kidney function is also lost as these organs are invaded. will lead to death within a year or two Several inexpensive serological tests that are easy to use have been developed to diagnose visceral leishmaniasis. These have generally replaced microscopic examination of blood and tissues to demonstrate the parasite. PCR tests confirm diagnosis but usually require a central laboratory first-line treatment in Europe and United States is liposomal amphotericin B, but it's relatively expensive for endemic countries. In many of these areas, conventional formulations of amphotericin B or meglumine antimoniate, which contains the toxic metal antimony, are in use first effective oral drug is miltefosine. It has demonstrated a cure rate as high as 82%, but it is teratogenic, resistance develops rapidly, and it is toxic to a significant number of recipients An inexpensive injectable aminoglycoside antibiotic, paromomycin, has shown good effectiveness.

Leishmaniasis

Leishmaniasis is a widespread and complex disease that exhibits several clinical forms. The protozoan pathogens are of about 20 Leishmania species, often categorized into three groups described below. transmitted by the bite of female sandflies, about 30 species of which are found in much of the tropical world and around the Mediterranean Small mammals are an unaffected reservoir of the protozoans. The infective form, the promastigote, is in the saliva of the insect. It loses its flagellum when it penetrates the skin of the mammalian victim, becoming an amastigote that proliferates in phagocytic cells, mostly in fixed locations in tissue. These amastigotes are then ingested by feeding sandflies, renewing the cycle Contact with contaminated blood from transfusions or shared needles can also lead to infection Visceral leishmaniasis has emerged as an important opportunistic infection associated with HIV. In southern Europe, up to 70% of cases of visceral leishmaniasis in adults are associated with HIV infection.

Listeriosis

Listeria monocytogenes is a gram-positive rod known to cause stillbirth and neurological disease in animals and disease Excreted in animal feces, it is widely distributed in soil and water. The name is derived from the proliferation of monocytes (a type of leukocyte) found in some animals infected by it Since the introduction of the Hibvaccination, listeriosis has become the fourth most common cause of bacterial meningitis The disease appears in two basic forms: in infected adults and as an infection of the fetus and newborn. In adult humans, it is usually a mild, often symptomless disease, but the microbe sometimes invades the CNS, causing meningitis. This is most likely to happen to persons whose immune system is compromised, such as persons with cancer, diabetes, or AIDS, or who are taking immunosuppressive medications Recovering or apparently healthy individuals often shed the pathogen indefinitely in their feces when L. monocytogenes is ingested by phagocytic cells, it isn't destroyed; it even proliferates within them, primarily in the liver It also has the unusual capability of moving directly from one phagocyte to an adjacent one L. monocytogenes is especially dangerous when it infects a pregnant woman. She usually suffers no more than mild, flulike symptoms. The fetus, however, can be infected via the placenta, often resulting in an abortion or stillborn infant In some cases the disease isn't manifested until a few weeks after birth, usually as meningitis, which can result in significant brain injury or death The infant mortality rate associated with this type of infection is about 60%. In human outbreaks, the organism is mostly foodborne. It's frequently isolated from a wide variety of foods; ready-to eat deli meats and dairy products have been involved in several outbreaks. L. monocytogenes is one of the few pathogens capable of growth at refrigerator temperatures, which can lead to an increase in its numbers during a food's shelf life Diagnosis in humans depends on isolating and culturing the pathogen, usually from blood or cerebrospinal fluid. Penicillin G is the antibiotic of choice for treatment

bronchitis or bronchiolitis

Many of the same bacteria and viruses that infect the upper respiratory system can also infect the lower respiratory system As the bronchi become involved, bronchitis or bronchiolitis develops A severe complication of bronchitis is pneumonia, in which the pulmonary alveoli become involved

Aspergillosis

Many other opportunistic fungi may cause respiratory disease, particularly in hosts who are immunosuppressed or have been exposed to massive numbers of spores Aspergillosis is an important example; it is airborne by the conidia of Aspergillus fumigatus and other species of Aspergillus, which are widespread in decaying vegetation Compost piles are ideal sites for growth, and farmers and gardeners are most often exposed to infective amounts of these conidia.

Measles (Rubeola)

Measles (rubeola) is an extremely contagious viral disease spread by the respiratory route infectious before symptoms appear, quarantine is not an effective measure of prevention The measles vaccine, now usually administered as the MMR vaccine (measles, mumps, rubella), has almost eliminated measles in the United States there is no animal reservoir for measles, but because the virus is so much more infectious than smallpox, herd immunity is difficult to obtain many cases of measles today occur in children under age 1. Measles is especially hazardous to infants, who are more likely to have serious complications. In prevaccination days, measles was rare at this age because infants were protected by maternal antibodies derived from their mothers' recovery from the disease infection begins in the upper respiratory system. After an incubation period of 10 to 12 days, symptoms develop resembling those of a common cold. Soon, a macular rash appears, beginning on the face and spreading to the trunk and extremities Measles lesions of the oral cavity include Koplik's spots, small red spots with central blue-white specks, on the oral mucosa opposite the molars. The presence of Koplik's spots is a diagnostic indicator of measles Measles is an extremely dangerous disease, especially in infants and very old people. It is frequently complicated by middle ear infections or pneumonia caused by the virus itself or by a secondary bacterial infection Encephalitis strikes approximately 1 in 1000 measles victims; its survivors are often left with permanent brain damage As many as 1 in 3000 cases is fatal, mostly in infants A rare complication of measles (about 1 in 1,000,000 cases) is subacute sclerosing panencephalitis. Occurring mostly in men, it appears about 1 to 10 years after recovery from measles. Severe neurological symptoms result in death within a few years

Neisseria meningitidis Meningitis (Meningococcal Meningitis)

Meningococcal meningitis is caused by Neisseria meningitidis (the meningococcus) aerobic, gram-negative diplococcus with a polysaccharide capsule that is important to its virulence Like Hib and the pneumococcus, it is frequently present in the nose and throat of carriers without causing disease symptoms up to 40% of the population are a reservoir of infection Transmission is by droplet aerosols or direct contact with secretions symptoms of meningococcal meningitis are mostly caused by an endotoxin that is produced very rapidly and is capable of causing death within just a few hour The most distinguishing feature is a rash that does not fade when pressed case of meningococcal meningitis typically begins with a throat infection, leading to bacteremia and eventually meningitis It usually occurs in children under 2 years. Significant numbers of these children have residual damage, such as deafness. Death can occur within a few hours after the onset of fever; however, antibiotic therapy has helped reduce the mortality rate to about 9-12%. Without chemotherapy, mortality rates approach 80%. The meningococcus occurs in six capsular serotypes associated with invasive disease (A, B, C, W-135, X, and Y) occurring most often in infants who have not yet developed protective antibodies In arid regions of Africa and Asia, dry air causes the nasal mucous membranes to become less resistant to bacterial invasion widespread epidemics, mostly of serotype A and C. The three meningococcal serogroups that most commonly circulate and cause disease in the United States are B, C, and Y Vaccines containing polysaccharide capsular material of serogroups A, C, Y, and W-135 (sometimes simply referred to as W) have been available since the 1980s. The newer serogroup B (MenB) vaccine, licensed in 2014, contains bacterial surface proteins. MenB vaccine is recommended tor 16- to 23-year-olds who are at risk of contracting the disease during outbreaks. A previously rare serogroup called X, for which a vaccine is not available, emerged in sub-Saharan Africa during the 200

Disease of the reproductive system

Microbes causing infections of the reproductive systems are usually very sensitive to environmental stresses and require intimate contact for transmission. concept of "disease" implies obvious signs and symptoms. Because many persons infected by the more common sexually transmitted pathogens don't have apparent signs or symptoms, the term STI often seems more appropriate and is used in this book. More than 30 bacterial, viral, or parasitic infections have been identified as sexually transmitted. In the half of cases occur in 15- to 24-year-olds. Most bacterial STIs can be prevented by the use of condoms

Trichinellosis

Most infections by the small roundworm Trichinella spiralis, called trichinellosis are insignificant larvae, in encysted form, are located in muscles of the host. 4% of cadavers tested carried this parasite. severity of the disease is generally proportional to the number of larvae ingested. Ingesting raw or undercooked meat (especially bear, pig, cougar, or dog) puts a person at risk of infection Freezing pork for prolonged periods (for example, -23°C for 10 days) kills T. spiralis. However, freezing doesn't kill some species found in wild game, such as Trichinella nativa In the muscles of intermediate hosts such as pigs, the T. spiralis larvae are encysted in the form of short worms about 1 mm in length. When a human ingests the flesh of an infected animal, digestive action in the intestine removes the cyst wall. The organism then matures into the adult form The adult worms spend only about a week in the intestinal mucosa and produce larvae that invade tissue. Eventually, the larvae encyst in muscle (common sites include the diaphragm and eye muscles), where they are barely visible in biopsied specimens Symptoms of trichinellosis include fever, swelling around the eyes, and gastrointestinal upset. Small hemorrhages under the fingernails are often observed Biopsy specimens, as well as a number of serological tests, can be used in diagnosis. A serological ELISA test that detects the parasite in meats has been developed Treatment is administering albendazole or mebendazole to kill intestinal worms and corticosteroids to reduce inflammation Death is extremely rare

Pinworms

Most of us are familiar with the pinworm, Enterobius vermicularis tiny worm (females are 8-13 mm in length, males 2-5 mm) migrates out of the anus of the human host to lay its eggs, causing local itching Whole households may become infected Diagnosis is usually based on finding eggs around the anus. These can be viewed by pressing transparent cellulose tape, sticky side down, against the skin, transferring the tape to a microscope slide and viewing the slide under a microscope Such drugs as pyrantel pamoate (often available without a prescription) and mebendazole are usually effective in treatment

Neonatal Herpes

Neonatal herpes is a serious consideration for women of childbearing age. The virus can cross the placental barrier and affect the fetus, causing spontaneous abortion or serious fetal damage If untreated, a survival rate of only about 40% can be expected, and even treated survivors will have considerable disability Herpes infection of the newborn is most likely to have serious consequences when the mother acquires the initial herpes infection during the pregnancy If tests show a pregnant woman has no antibodies against herpes viruses, she requires special counseling to avoid an initial infection. Exposure to recurrent or asymptomatic herpes is much less likely to damage the fetus, most likely because of protective maternal antibodies Most infections of the newborn occur from exposure to HSV during delivery. HSV-2 infections are likely to be more serious than HSV-1 infections If genital sores that might be caused by herpes infection are present at the time of delivery, a sample can be taken and isolates tested to determine whether they are HSV-1 or HSV-2 If the culture is negative but a herpes infection is still suspected, a PCR test for viral DNA can be done It is rather common for pregnant women to be shedding HSV-2 even though they show no evidence of an infection Even so, fewer than 1% of newborns develop neonatal herpes, which is also probably because of protective antibodies. Some newborns have infections that are confined to the skin, mucous membranes, and eyes. With proper treatment, the outcome of these cases is usually good However, about 30% of the cases are associated with damage to the central nervous system that may include developmental delays, blindness, hearing loss, or epilepsy Culture and identification of the virus take a few days, but fluorescent antibody tests can quickly detect viral protein, or PCR tests can detect the presence of viral DNA Treatment usually involves intravenous administration of acyvlovir. No vaccine is currently available.

normal microbiota of urinary system

Normal urine is not sterile and may become contaminated with microbiota of the skin near the end of its passage through the urethra. Therefore, urine collected directly from the urinary bladder has fewer microbial contaminants than voided urine predominant bacteria in the vagina are the lactobacilli. These bacteria produce lactic acid, which maintains the acidic pH (3.8 to 4.5) of the vagina, inhibiting the growth of most other microbes. Most vaginal lactobacilli produce hydrogen peroxide, which also inhibits growth of other bacteria. Estrogens promote the growth of lactobacilli by enhancing the production of glycogen by vaginal epithelial cells. The glycogen quickly breaks down into glucose, which the lactobacilli metabolize into lactic acid. Other bacteria, such as streptococci, various anaerobes, and some gram-negatives, are also found in the vagina yeastlike fungus Candida albicans is part of the normal microbiota of 10-25% of women, even when they are asymptomatic Pregnancy and menopause are often associated with higher rates of urinary tract infections. The reason is that estrogen levels are lower, resulting in lower populations of lactobacilli and therefore less vaginal acidity Semen picks up bacteria from the urethra; however, the recently discovered microbiome of the seminal vesicles, including Proprionibacterium, Corynebacterium, and Pseudomonas, may affect sperm production The urinary system normally contains few microbes, but it's subject to opportunistic infections that can be quite troublesome. Almost all such infections are bacterial, although occasional infections by schistosome parasites, protozoa, and fungi occur

Clostridium perfringens gastroenteritis

One of the more common, if underrecognized, causes of food poisoning in the United States is caused by Clostridium perfringens, a large, gram-positive, endospore-forming, obligately anaerobic rod. This bacterium is also responsible for human gas gangrene outbreaks of Clostridium perfringens gastroenteritis are associated with meats or meat stews contaminated with intestinal contents of the animal during slaughter. Such foods meet the pathogen's nutritional requirement for amino acids, and when the meats are cooked, the oxygen level is lowered enough for clostridial growth The endospores survive most routine heatings, and the generation time of the vegetative bacterium is less than 20 minutes under ideal conditions grows in the intestinal tract and produces an exotoxin that causes the typical symptoms of abdominal pain and diarrhea Most cases are mild and self-limiting and probably are never clinically diagnosed If treatment is required, oral rehydration is recommended. The symptoms usually appear 8 to 12 hours after ingestion Diagnosis is based on finding at least 106 C. perfringens endospores per gram of stool within 48 hours of the onset of illness

otitis media

One of the more uncomfortable complications of the common cold, or of any infection of the nose or throat, is infection of the middle ear, otitis media, or earache formation of pus, which builds up pressure against the eardrum and causes it to become inflamed and painful number of bacteria can cause otitis media. Until this century, S. pneumoniae was the most common cause of otitis media. The conjugate vaccine to prevent S. pneumoniae pneumonia has reduced the incidence The bacteria most frequently involved are other S. pneumoniae, nonencapsulated H. influenzae, Moraxella catarrhalis and S. pyogenes In about 30% of cases, no bacteria can be detected. Viral infections may be responsible in these instances; respiratory syncytial viruses ( are the most common isolate Otitis media affects 85% of children before the age of 3 and accounts for nearly half of office visits to pediatricians—an estimated 8 million cases each year in the United States. It is estimated that ear infections account for about one-fourth of the prescriptions for antibiotics; however, antibiotics should be prescribed only if the infection is caused by a bacterium Broad-spectrum penicillins, such as amoxicillin, are usually the first choice for children

Hydatid disease

One of the most dangerous tapeworms is Echinococcus granulosus, only a few millimeters in length Dogs shed the tapeworm eggs in their feces, which are ingested by grazing mammals. Once ingested, the eggs hatch and develop into cysts in the internal organs Once ingested by a human, the eggs of E. granulosus hatch, and larvae may migrate to various tissues of the body. The liver and lungs are the most common sites, but the brain and numerous other sites also may be infected Once in place, the egg develops into a hydatid cyst that can grow to a diameter of 1 cm in a few months In some locations, cysts may not be apparent for many years. Some, where they are free to expand, become enormous, containing up to 15 liters (4 gallons) of fluid. Damage may arise from the size of the cyst in such areas as the brain or the interior of bones If the cyst ruptures in the host, it can lead to the development of a great many daughter cysts. Another factor in the pathogenicity of such cysts is that the fluid contains proteinaceous material to which the host becomes sensitized If the cyst suddenly ruptures, the result can be life-threatening anaphylactic shock For diagnosis, several serological tests that detect circulating antibodies are useful in screening. If available, physical imaging methods such as X rays, CT, and MRI are best Treatment is usually surgical removal, but care must be taken to avoid release of the fluid and the potential spread of infection or anaphylactic shock. If removal isn't feasible, the drug albendazole can kill the cysts.

Congenital Syphilis

One of the most distressing and dangerous forms of syphilis, called congenital syphilis, is transmitted across the placenta to the unborn fetus. Damage to mental development and other neurological symptoms are among the more serious consequences most common when pregnancy occurs during the latent period of the disease. A pregnancy during the primary or secondary stage is likely to produce a stillbirth Treating the mother with antibiotics during the first two trimesters (6 months) will usually prevent congenital transmission.

Escherichia coli

One of the most prolific microorganisms in the human intestinal tract is Escherichia coli. Bc it's so common and so easily cultivated, microbiologists often regard it as something of a laboratory pet E. coli are normally harmless, but certain strains can be pathogenic Mobile genetic elements can turn E. coli into a highly adapted pathogen causing a range of diseases. Some toxin-secreting pathogenic strains are well adapted to invasion of intestinal epithelial cells, causing E. coli gastroenteritis. Other locations, such as the urinary tract, bloodstream, and central nervous system, can also be affected Five pathogenic varieties (pathotypes) of E. coli have been well characterized Enteropathogenic E. coli (EPEC) is a major cause of diarrhea in developing countries and is potentially fatal in infants bacteria attaches to the intestinal wall, they eliminate surrounding microvilli and stimulate host-cell actin to form pedestals beneath their site of attachment. EPEC bacteria secrete a number of effector proteins that are translocated into host cells, some contributing to diarrhea

Ascariasis

One of the most widespread helminthic infections is ascariasis, caused by Ascaris lumbricoides with a reported incidence of 20-60% in the childhood population. Worldwide, perhaps 30% of the population is infected Diagnosis is often made when an adult worm emerges from the anus, mouth, or nose These worms can be quite large, up to 30 cm (about 1 ft) in length (Figure 25.25) In the intestinal tract, they live on partially digested food and cause few symptoms worm's life cycle begins when eggs (upwards of 200,000 per day) are shed in a person's feces and, under poor sanitary conditions, are ingested by another person. In the upper intestine, the eggs hatch into small wormlike larvae that pass into the bloodstream and then into the lungs. There they migrate into the throat and are swallowed. The larvae develop into egglaying adults in the intestines. In the lungs, the tiny larvae may cause some pulmonary symptoms. Extremely large numbers may block the intestine, bile duct, or pancreatic duct The worms do not usually cause severe symptoms, but their presence can be manifested in distressing ways. The most dramatic consequences of infection with A. lumbricoides are from the migrations of adult worms. Worms have been known to leave the body of small children through the umbilicus (navel) and to escape through the nostrils of a sleeping person. Microscopic examination of feces for eggs is used for diagnosis effectively treated with mebendazole or albendazole.

subacute bacterial endocarditis

One type of bacterial endocarditis, subacute bacterial endocard is characterized by fever, general weakness, and a heart murmur. It is usually caused by alpha-hemolytic streptococci (most often, Streptococcus viridans), which are common in the oral cavity, although enterococci or staphylococci may also be involved. The condition probably arises from a focus of infection elsewhere in the body, such as in the teeth or tonsils. Microorganisms are released by tooth extractions or tonsillectomies, enter the blood, and find their way to the heart. Normally, such bacteria would be quickly cleared from the blood by the body's defensive mechanisms. However, in people whose heart valves are abnormal, because of either congenital heart defects or such diseases as rheumatic fever and syphilis, the bacteria lodge in the preexisting lesions. Within the lesions, the bacteria multiply and become entrapped in blood clots that protect them from phagocytes and antibodies. As multiplication progresses and the clot gets arger, pieces of the clot break off and can block blood vessels or lodge in the kidneys. In time, the function of the heart valves is impaired. Left untreated by appropriate antibiotics, subacute bacterial endocarditis is fatal within a few months

Prevention of Rabies

Only high-risk individuals, such as laboratory workers, animal control professionals, and veterinarians, are routinely vaccinated against rabies before known exposure If a person is bitten, the wound should be thoroughly washed with soap and water. If the animal is positive for rabies, the person must undergo post exposure prophylaxis (PEP)—meaning a series of antirabies vaccine and immune globulin injections Another indication for anti rabies treatment is any unprovoked bite by a skunk, bat, fox, coyote, bobcat, or raccoon not available for examination Treatment after a dog or cat bite, if the animal cannot be found, is determined by the prevalence of rabies in the area CDC recommends PEP after any significant encounter with a bat—unless the bat can be tested and shown to be negative for rabies human diploid cell vaccine (HDCV), or chick embryo-grown vaccines. These vaccines are administered in a series of four injections at intervals during a 14-day period. Passive immunization is provided simultaneously by injecting human rabies immune globulin (RIG) that has been harvested from people who are immunized against rabies.

Yersinia enterocolitica

Other enteric pathogens being identified with increasing frequency are Yersinia enterocolitica and Y. pseudotuberculosis gramnegative bacteria are intestinal inhabitants of many domestic animals and are most often transmitted by eating raw or undercooked pork Both microbes are distinctive in their ability to grow at refrigerator temperatures of 4°C. This ability increases their numbers in stored refrigerated blood, to the extent that their endotoxins can result in shock to the blood recipient Yersinia has occasionally been the cause of severe reactions when it contaminates transfused blood. symptoms are diarrhea, fever, headache, and abdominal pain. The pain is often severe enough to cause a misdiagnosis of appendicitis Diagnosis requires culturing the organism, which can then be identified using biochemical or molecular tests Adults suffering from yersiniosis usually recover in 1 or 2 weeks; children may take longer Treatment with antibiotics and oral rehydration may be helpful.

Pelvic inflammatory disease (PID)

Pelvic inflammatory disease (PID) is a collective term for any extensive bacterial infection of the female pelvic organs, particularly the uterus, cervix, uterine tubes, or ovaries During their reproductive years, one in ten women suffers from PID, and one in four of these will have serious complications, such as infertility or chronic pain Pelvic inflammatory disease is considered to be a polymicrobial infection—that is, a number of different pathogens might be the cause, including coinfections. two most common microbes are N. gonorrhoeae and C. trachomatis. The onset of chlamydial PID is relatively more insidious, with fewer initial inflammatory symptoms than when caused by N. gonorrhoeae. the damage to the uterine tube may be greater with chlamydia, especially with repeated infections The bacteria may attach to sperm cells and be transported by them from the cervical region to the uterine tubes. Women who use barrier contraceptives, especially with spermicides, have a significantly lower rate of PID Infection of the uterine tubes, or salpingitis, is the most serious form of PID. Salpingitis can result in scarring that blocks the passage of ova from the ovary to the uterus, possibly causing sterility One episode of salpingitis causes infertility in 10-15% of women; 50-75% become infertile after three or more such infections A blocked uterine tube may cause a fertilized ovum to be implanted in the tube rather than the uterus. This is called an ectopic (or tubal) pregnancy, and it is life-threatening because of the possibility of rupture of the tube and resulting hemorrhage. The reported cases of ectopic pregnancies have been increasing steadily, corresponding to the increasing occurrence of PID A diagnosis of PID depends strongly on signs and symptoms, in combination with laboratory indications of a gonorrheal or chlamydial infection of the cervix. treatment for PID is the simultaneous administration of doxycycline and cefotetan (a β-lactam). This combination is active against both the gonococcus and chlamydia

Diagnosis of Tuberculosis

People infected with tuberculosis respond with cell-mediated immunity against the bacterium This form of immune response, rather than humoral immunity, develops because the pathogen is located mostly within macrophages involves sensitized T cells, is the basis for the tuberculin skin test, a screening test for infection A positive test does not necessarily indicate active disease In this test, a purified protein derivative of the tuberculosis bacterium, derived by precipitation from broth cultures, is injected cutaneously. If the injected person has been infected with TB in the past, sensitized T cells react with these proteins, and a delayed hypersensitivity reaction occurs in about 48 hours. This reaction appears as an induration (hardening) and reddening of the area around the injection site. In this test, known as the Mantoux test, dilutions of 0.1 ml of antigen are injected and the reacting area of the skin is measured A positive tuberculin test in the very young is a probable indication of an active case of TB In older individuals, it might indicate only hypersensitivity resulting from a previous infection or vaccination, not a current active case The initial step in laboratory diagnosis of active cases is a microscopic examination of smears, such as sputum Confirming a diagnosis of TB by isolating the bacterium poses difficulties because the pathogen grows very slowly. A colony might take 3 to 6 weeks to form, and completing a reliable identification series may add another 3 to 6 weeks Blood tests measure release of IFN-γ from white blood cells after exposure to mycobacterial antigen in a test tube. They are the preferred tests for a person who has received BCG vaccinations. Nucleic acid amplification tests (NAATs) can detect M. tuberculosis 1 to 2 weeks sooner than cultures and at the same time can determine resistance to a major TB antibiotic, rifampin They do not distinguish latent from active infection. These assays seem likely to replace the tuberculin skin test for many uses, especially where cross-reactivity with BCG vaccination is a problem

Pneumocystis pneumonia (PCP)

Pneumocystis pneumonia (PCP) is caused by Pneumocystis jirovecii ; taxonomic position of this microbe has been uncertain ever since its discovery in 1909, no universal agreement about whether it is a protozoan or a fungus It has some characteristics of both groups Analysis of RNA and certain other structural characteristics indicate that it's closely related to certain yeasts, and it's usually reported as a fungus The pathogen is sometimes found in healthy human lungs. Immunocompetent adults have few or no symptoms, but newly infected infants occasionally show symptoms of a lung infection This population may also be the reservoir of the organism, which is not found in the environment, animals, or very often in healthy humans By 1993, it had become a primary indicator of AIDS, with more than 20,000 annual reported cases. Presumably, the loss of an effective immune defense allows the activation of a latent infection the microbes are found mostly in the lining of the alveoli. Diagnosis is usually made from sputum samples in which cysts are detected. There, they form a thickwalled cyst in which spherical intracystic bodies successively divide as part of a sexual cycle. The mature cyst contains eight such bodies. Eventually the cyst ruptures and releases them, and each body develops into a trophozoite. the trophozoite cells can reproduce asexually by fission, but they may also enter the encysted sexual stage. The fatality rate is 100% without treatment. The drug of choice for treatment is currently trimethoprim-sulfamethoxazole

Pneumococcal Pneumonia

Pneumonia caused by S. pneumoniae is called pneumococcal pneumonia. S. pneumoniae is a gram-positive, ovoid bacterium common cause of otitis media, meningitis, and sepsis. cell pairs are surrounded by a dense capsule that makes the pathogen resistant to phagocytosis. These capsules are also the basis of serological differentiation of pneumococci into at least 90 serotypes. Most human infections are caused by only 23 variants, and these are the basis of current vaccines. involves both the bronchi and the alveoli Symptoms include high fever, breathing difficulty, and chest pain. (Atypical pneumonias usually have a slower onset and less fever and chest pain) The lungs have a reddish appearance because blood vessels are dilated. In response to the infection, alveoli fill with some red blood cells, neutrophils, and fluid from surrounding tissues sputum is often rust colored from blood coughed up from the lungs Pneumococci can invade the bloodstream, the pleural cavity surrounding the lung, and occasionally the meninges No bacterial toxin has been clearly related to pathogenicity A presumptive diagnosis can be made by isolating the pneumococci from the throat, sputum, and other fluids. Pneumococci can be distinguished from other alpha-hemolytic streptococci by observing the inhibition of growth next to a disk of optochin (ethylhydrocupreine hydrochloride) or by performing a bile solubility test A latex indirect agglutination test that detects a capsule antigen of S. pneumoniae in the urine can be performed in a physician's office and, with 93% accuracy, can make a diagnosis in 15 minutes There are many healthy carriers of the pneumococcus. Virulence of the bacteria seems to be based mainly on the carrier's resistance, which can be lowered by stress A recurrence of pneumococcal pneumonia is not uncommon, but the serological types are usually different Antibiotic resistance is an increasing problem treatment usually begins with a broad-spectrum cephalosporin until antibiotic-sensitivity testing is don; Possible drugs include a b-lactam, macrolide, or fluoroquinoline A conjugated pneumococcal vaccine has been effective in preventing infection by the 13 serotypes included in it. It has also had an indirect herd effect shown by reduction in other diseases, such as otitis media, attributable to the pneumococcus The pneumococcal polysaccharide vaccine, recommended for people with asthma and for older adults, protects against 23 strains of the bacteria.

Diagnosis of polio

Polio is usually diagnosed by isolating the virus from feces and throat secretions Cell cultures can be inoculated, and cytopathic effects on the cells can be observed

Poliomyelitis (polio)

Poliomyelitis (polio) the paralytic form of poliomyelitis affects fewer than 1% of people infected great majority of cases are asymptomatic or exhibit only mild symptoms, such as headache, sore throat, fever, and nausea Polio made its first appearance in the United States in an outbreak in Vermont in the summer of 1894 outbreaks increasingly affected adolescents and young adults, and the number of paralytic cases steadily increased Many victims died as their respiratory muscles were paralyzed, and thousands of infants and youths were left with their extremities permanently crippled The primary mode of transmission is ingestion of water contaminated with feces containing the virus. Improved sanitation delayed exposure to polioviruses in feces until after the protection provided by maternal antibodies had waned At one time, exposure to the poliovirus was frequent. Infants were usually exposed to poliovirus while still protected by maternal antibodies. The result was usually an asymptomatic case of the disease and a lifelong immunity. When infection is delayed until adolescence or early adulthood, the paralytic form of the disease appears more frequently. bc the infection begins when the virus is ingested, its primary areas of multiplication are the throat and small intestine, initial sore throat and nausea. Next, the virus invades the tonsils and the lymph nodes of the neck and ileum (the terminal portion of the small intestine). From the lymph nodes, the virus enters the blood, resulting in viremia. In most cases the viremia is only transient, the infection does not progress past the lymphatic system, and clinical disease does not result. If the viremia persists, however, the virus eventually penetrates the capillary walls and enters the CNS. Once in the CNS, the virus displays a high affinity for nerve cells, particularly motor nerve cells in the upper spinal cord does not infect the peripheral nerves or the muscles. As the virus multiplies within the cytoplasm of the motor nerve cells, the cells die, and paralysis results. Death can result from respiratory failure

Kawasaki syndrome (KS)

Probably the most common cause of acquired heart disease in the United States (replacing rheumatic fever) is an acute febrile illness of unknown etiology, Kawasaki syndrome (KS) most often affects younger children, especially boys under the age of 5. Patients with the disease suffer a high and persistent fever, widespread skin rash, and swelling of the hands and feet and of the lymph glands in the neck. Without treatment, mortality may be about 1% but is much lower with effective treatment, involving aspirin (which affects blood clotting) and an intravenously administered immunoglobulin KS is diagnosed primarily from its clinical signs and symptoms; there is no laboratory test available KS may be triggered by an infection, although no specific pathogen is known.

epiglottitis,

Probably the most threatening infectious disease of the upper respiratory system is epiglottitis, inflammation of the epiglottis flaplike structure of cartilage that prevents ingested material from entering the larynx Epiglottitis is a rapidly developing disease that can result in death within a few hours. It is caused by opportunistic pathogens, usually Haemophilus influenzae type b Hib vaccine, although directed primarily at meningitis, has significantly reduced the incidence of epiglottitis in the vaccinated population.

Puerperal Sepsis

Puerperal sepsis, also called puerperal fever and childbirth fever, is an HAI begins as an infection of the uterus as a result of childbirth or abortion Streptococcus pyogenes, a group A beta-hemolytic streptococcus, is the most frequent cause, although other organisms may cause infections of this type. Puerperal sepsis progresses from an infection of the uterus to an infection of the abdominal cavity (peritonitis) and in many cases to sepsis Antibiotics, especially penicillin, and modern hygienic practices have now made S. pyogenes puerperal sepsis an uncommon complication of childbirth.

Rabies

Rabies (the word is from the Latin for rage or madness) is a disease that almost always results in fatal encephalitis The causative agent is the rabies virus, a member of the genus Lyssavirus having a characteristic bullet shape Lyssaviruses (lyssa, from the Greek for frenzy) are single-stranded RNA viruses with no proofreading capability, and mutant strains develop rapidly. humans usually are infected with the rabies virus in saliva from the bite of an infected animal—especially dogs. On rare occasions, the virus can be transmitted through fresh skin abrasions and may cross the mucous membranes of the nose, mouth, and even eyes The virus proliferates in the PNS and moves, fatally, toward the CNS deaths from rabies are frequently misdiagnosed, several cases of rabies have been traced to transplanted body tissues, especially corneas Rabies is unique in that the incubation period is usually long enough to allow immunity to develop from post exposure vaccination The natural immune response is ineffective because the viruses are introduced into the wound in numbers too low to provoke it; also, they do not travel through the bloodstream or lymphatic system, where the immune system could best respond Initially, the virus multiplies in skeletal muscle and connective tissue, where it remains localized for periods ranging from days to months. Then it enters a motor neuron and travels, at the rate of 15 to 100 mm per day, along peripheral nerves to the CNS, where it causes encephalitis incubation periods average is 30 to 50 days Bites in areas rich in nerve fibers, such as the hands and face, are especially dangerous, and the resulting incubation period tends to be short Once the virus enters the peripheral nerves, it isn't accessible to the immune system until cells of the CNS begin to be destroyed, which triggers a belated and ineffective immune response Preliminary symptoms are mild and varied, resembling several common infections When the CNS becomes involved, the patient tends to alternate between periods of agitation and intervals of calm. At this time, a frequent symptom is spasms of the muscles of the mouth and pharynx that occur when the patient feels air drafts or swallows liquids. In fact, even the mere sight or thought of water can set off the spasms—thus the common name hydrophobia (fear of water) The final stages of the disease result from extensive damage to the nerve cells of the brain and the spinal cord.

Distribution of Rabies

Rabies occurs all over the world, mostly a result of dog bites rabies is widespread among wildlife, predominantly bats, skunks, foxes, and raccoons, although it is also found in domesticated animals As many as 40,000 people are administered post exposure rabies vaccine each year, often as a precaution when the rabies status of the biting animal cannot be determined Rabies is almost never found in squirrels, rabbits, rats, or mice In the United States, 7000 to 8000 cases of rabies are diagnosed in animals each year, but in recent years, only one to six cases have been diagnosed in humans annually

Rotavirus

Rotavirus is the most common cause of viral gastroenteritis, especially in children Acquired immunity then makes rotavirus infections, except for certain strains, much less common in adults following an incubation period of 2 to 3 days, the patient suffers from low-grade fever, diarrhea, and vomiting, which persists for about a week rotavirus cases usually peak during the cooler winter months In 2006 a live, orally administered vaccine was licensed. Before the vaccine, more than 90% of children in the United States were infected by the age of 3 In some cases, parents also become infected. The vaccine has decreased incidence by 98% infections are routinely diagnosed by several types of commercially available tests, such as enzyme immunoassays Treatment is usually limited to oral rehydration therapy

Rubella

Rubella, or German measles is a much milder viral disease than rubeola (measles) and often goes undetected macular rash of small red spots and a light fever are the usual symptoms Complications are rare, especially in children, but encephalitis occurs in about 1 case in 6000, mostly in adults transmitted by the respiratory route, and an incubation of 2 to 3 weeks is the norm. Recovery from clinical or subclinical cases appears to give a firm immunity certain severe birth defects were associated with maternal infection during the first trimester (3 months) of pregnancy, a condition called congenital rubella syndrome. If a pregnant woman contracts the disease during this time, there is about a 35% incidence of serious fetal damage, including deafness, eye cataracts, heart defects, mental retardation, autism spectrum disorder, and death. Some 15% of babies with congenital rubella syndrome die during their first year important to identify women of childbearing age who are not immune to rubella rubella vaccine was introduced in 1969. Follow-up studies indicate that more than 90% of vaccinated individuals are protected for at least 15 years vaccine is not recommended for pregnant women. However, in hundreds of cases in which women were vaccinated 3 months before or 3 months after their presumed date of conception, no case of congenital rubella syndrome defects has occurred.

Schistosomiasis

Schistosomiasis is a debilitating disease caused by a small fluke. It is probably second only to malaria in the number of people it kills or disables symptoms of the disease result from eggs shed by adult schistosomes in the human host. These adult helminths are 15 to 20 mm long, and the slender female lives permanently in a groove in the body of the male, from which is derived the name: schistosome, or split-body The union between the male and female produces a continuing supply of new eggs. Some of these eggs lodge in tissues. Defensive reactions of the human host to these foreign bodies cause local tissue damage called granulomas. Other eggs are excreted and enter the water to continue the cycle The disease is spread by human feces or urine carrying eggs of the schistosome that enter water supplies with which humans come into contact Also, snails of certain species are essential for one stage of the life cycle of the schistosomes They produce the cercariae that penetrate the skin of a human entering contaminated water. In most areas of the United States, a suitable host snail isn't present. two primary types of schistosomiasis. Schistosoma haematobium, sometimes called urinary schistosomiasis results in inflammation of the urinary bladder wall S. haemotobium, S. japonicum, and S. mansoni cause intestinal inflammation Depending on the species, schistosomiasis can cause damage to many different organs when eggs migrate in the bloodstream to different areas—for example, damage to the liver or lungs, urinary bladder cancer, or, when eggs lodge in the brain, neurological symptoms Geographically, S. japonicum is found in east Asia. S. haematobium infects many people throughout Africa and the Middle East, most particularly Egypt. S. mansoni has a similar distribution but also is endemic in South America and the Caribbean, including Puerto Rico adult worms appear to be unaffected by the host's immune system. bc quickly coat themselves with a layer that mimics the host's tissues. Laboratory diagnosis consists of microscopic identification of the flukes or their eggs in fecal and urine specimens, intradermal tests, and serological tests such as complement-fixation and precipitin test treated with praziquantel. Sanitation and elimination of the host snail are also useful forms of control.

Gram-Negative Sepsis

Septic shock is most likely to be caused by gram-negative bacteria endotoxins can cause a severe drop in blood pressure with its associated signs and symptoms. Septic shock is often called by the alternative names gram-negative sepsis or endotoxic shock. Less than one-millionth of a milligram of endotoxin is enough to cause the symptoms Klebsiella spp., E. coli, and Pseudomonas aeruginosa are most frequently involved. Recent outbreaks of an emerging pathogen, Elizabethkingia spp., have occurred in the United States progression to lethal stages is rapid and generally impossible to treat effectively. Administering antibiotics then may even aggravate the condition by causing the lysis of large numbers of bacteria that then release more endotoxins In addition to antibiotics, treatment of septic shock involves attempts to neutralize the LPS components and inflammationcausing cytokines

Norovirus

Several similar viruses were later identified, and this group was termed Norwalk-like viruses. All were determined to be members of the caliciviruses and are now termed noroviruses It is not practical to culture them, and they do not infect the usual laboratory animals Humans become infected by fecal-oral transmission from food and water and even aerosols from vomiting. The infectious dose may be as low as 10 viruses. The viruses continue to be shed for several days after the patient is asymptomatic About half of adult Americans show serological evidence that they have been infected The currently dominant strain of noroviruses made its appearance around 2002, which is attributed to several possible factors. This strain may be more virulent, or more environmentally stable; also, fewer people may have had resistance to it from previous exposure Natural resistance to a particular strain may last only a few months—at most about 3 years Cleanup and prevention of transmission following an outbreak on a cruise ship or restaurant, for example, has proved to be a challenging problem. The viruses are unusually persistent on environmental surfaces, including door handles or elevator buttons The noroviruses don't have a lipid envelope and are, therefore, not reliably inactivated by ethanol. Most of the effectiveness of such measures is probably related to mechanical removal, as with hand soap. To decontaminate hard, nonporous surfaces requires solutions containing 1000 to 5000 ppm of hypochlorite To detect noroviruses in stool samples, laboratories use sensitive PCR and enzyme immunoassay (EIA) tests. The availability of such new and sensitive assays has led to recognition of noroviruses as the most common cause (at least half of recent foodborne outbreaks in the United States) of nonbacterial gastroenteritis incubation period of 18 to 48 hours, the patient suffers from vomiting and/or diarrhea for 2 or 3 days. Diarrhea is the most prevalent symptom in children; most adults experience diarrhea, although many adult patients experience only vomiting severity of symptoms often depends upon the size of the infectious dose only treatment for viral gastroenteritis is oral rehydration or, in exceptional cases, intravenous rehydration

Secondary Stage Syphilis

Several weeks after the primary stage the disease enters the secondary stage, characterized mainly by oral sores and skin rashes of varying appearance rash is widely distributed on the skin and mucous membranes and is especially visible on the palms and on the soles The damage done to tissues at this stage and the later tertiary stage is caused by an inflammatory response to circulating immune complexes that lodge at various body sites Other symptoms often observed are the loss of patches of hair, malaise, and mild fever. A few people may exhibit neurological symptoms At this stage, the lesions of the rash contain many spirochetes and are very infectious Transmission from sexual contact occurs during the primary and secondary stages. Such nonsexual transmission is possible, but the microbes don't survive long on environmental surfaces and are very unlikely to be transmitted via such objects as toilet seats Secondary syphilis is a subtle disease; at least half of the patients diagnosed with this stage can recall no lesions at all. Symptoms usually resolve within 3 months.

Rhizopus and Mucor

Similar pulmonary infections sometimes result when individuals are exposed to spores of other mold genera, such as Rhizopus and Mucor Such diseases can be very dangerous, particularly invasive infections of pulmonary aspergillosis. Predisposing factors include an impaired immune system, cancer, and diabetes As with most systemic fungal infections, there is only a limited arsenal of antifungal agents available; itraconazole and amphotericin B have proved the most useful

Smallpox (Variola)

Smallpox is caused by an orthopoxvirus known as the smallpox (variola) virus There are two basic forms of this disease: variola major, with a mortality rate of 20-60% and over 80% in children, and variola minor, with a mortality rate of less than 1%. Transmitted by the respiratory route, the viruses infect many internal organs before they eventually move into the bloodstream, infecting the skin and producing more recognizable symptoms. The growth of the virus in the epidermal layers of the skin causes lesions that become pustular after 10 days Complications from the smallpox vaccine can be treated with vaccinia immune globulin, which contains antibodies to the virus. The antiviral drug, cidofovir, can also be administered. With the disappearance of smallpox, there has been some concern with a similar disease, monkeypox. Monkeypox closely resembles smallpox in symptoms and, while smallpox was endemic, was probably mistaken for it. The monkeypox virus, like smallpox virus, is an orthopoxvirus, and vaccination for smallpox has a protective effect. Monkeypox is known to jump from animals to humans, but fortunately its transmission from human to human has been very limited

Testing for Drug Susceptibility

Solid-media culture-based methods for drug susceptibility testing can take as long as 4 to 8 weeks for finalized results M. tuberculosis grows faster in liquid media. These assays are simultaneously useful for both diagnosis and determination of drug susceptibility. liquid cultures, requires only 6 to 8 days, and is relatively inexpensive determination of susceptibility for rifampin can be considered a marker for potential resistance to other drugs NAATs also rapidly test for rifampin resistance. NAATs are needed to determine resistance to the other first-line and second-line anti-TB drugs The biggest problem is that most drug resistance, aside from resistance to rifampin, is not due to a single gene. One new test, MTBDRsl, does identify resistance to fluoroquinolones.

flesh-eating bacteria,

Some 1000 cases of invasive group A streptococcal infection, caused by the "flesh-eating bacteria," occur each year in the United States precipitated by minor breaks in the skin, and early symptoms are often unrecognized, delaying diagnosis and treatment—with serious consequences. Once established, necrotizing fasciitis may destroy tissue as rapidly as a surgeon can remove it, and mortality rates from systemic toxicity can exceed 40%. Streptococci are considered the most common causative organism, although other bacteria cause similar conditions. Pyrogenic toxins produced by certain streptococcal M-protein types act as superantigens, causing the immune system to contribute to the damage. Broadspectrum antibiotics are usually prescribed because of the possibility that multiple bacterial pathogens are present. Necrotizing fasciitis is often associated with streptococcal toxic shock syndrome (streptococcal TSS), which resembles staphylococcal TSS In cases of streptococcal TSS, a rash is less likely to be present, but bacteremia is more likely to occur. M proteins shed from the surfaces of these streptococci form a complex with fibrinogen that binds to neutrophils. This causes activation of neutrophils, precipitating the release of damaging enzymes and consequent shock and organ damage. The mortality rate is much higher than with staphylococcal TSS—up to 80% has been reported.

intoxication

Some pathogens cause disease by forming toxins that affect the GI tract An intoxication is caused by the ingestion of such a preformed toxin. Most intoxications, such as that caused by Staphylococcus aureus, are characterized by a very sudden appearance (usually in only a few hours) of symptoms of a GI disturbance Fever is less often one of the symptoms

rheumatic fever

Streptococcal infections, such as those caused by Streptococcus pyogenes, sometimes lead to rheumatic fever, which is generally considered an autoimmune complication. It occurs primarily in people aged 4 to 18 and often follows an episode of streptococcal sore throat. The disease is usually first expressed as a short period of arthritis and fever. Subcutaneous nodules at joints often accompany this stage In about half of persons affected, an inflammation of the heart, probably from a misdirected immune reaction against streptococcal M protein, damages the valves. Reinfection with streptococci renews the immune attack. Damage to heart valves may be serious enough to result in eventual failure and death. People who have had an episode of rheumatic fever are at risk of renewed immunological damage with repeated streptococcal sore throats. The bacteria have remained sensitive to penicillin, and patients at particular risk, such as these, often receive a monthly preventive injection of long-acting penicillin G benzathine 10% of people with rheumatic fever develop Sydenham's chorea, an unusual complication known in the Middle Ages as Saint Vitus' dance. Several months following an episode of rheumatic fever, the patient (much more likely to be a girl than a boy) exhibits purposeless, involuntary movements during waking hours. Occasionally, sedation is required to prevent self-injury from flailing arms and legs. The condition disappears after a few months.

Streptococcal pharyngitis (strep throat)

Streptococcal pharyngitis (strep throat) is an upper respiratory infection caused by group A streptococci (GAS) gram-positive bacterial group consists solely of Streptococcus pyogenes, the same bacterium responsible for many skin and soft tissue infections, such as impetigo, erysipelas, and acute bacterial endocarditis Pharyngitis is characterized by local inflammation and a fever. Frequently, tonsillitis occurs, and the lymph nodes in the neck become enlarged and tender. Another frequent complication is otitis media pathogenicity of GAS is enhanced by their resistance to phagocytosis. They are also able to produce special enzymes, called streptokinases, which lyse fibrin clots, and streptolysins, which are cytotoxic to tissue cells, red blood cells, and protective leukocytes rapid antigen detection tests that were capable of detecting GAS directly on throat swabs became available. A physician can perform a rapid test in the office. These rapid tests have high specificity. However, negative samples should be cultured because of the varying sensitivity of these tests. majority of patients seen for sore throats do not have a streptococcal infection. Some cases are caused by other bacteria, but most are caused by viruses—for which antibiotic therapy is ineffective GAS should be confirmed and treated in children older than 3 years to prevent development of rheumatic fever have remained sensitive to penicillin Pharyngitis is now most commonly transmitted by respiratory secretions, but epidemics of streptococcal pharyngitis spread by unpasteurized milk were once frequent.

Streptococcus pneumoniae Meningitis (Pneumococcal Meningitis)

Streptococcus pneumoniae, like H. influenzae, is a common inhabitant of the nasopharyngeal region. 70% of the general population are healthy carriers. The pneumococcus, so called because it is best known as a cause of pneumonia is a gram-positive, encapsulated diplococcus leading cause of bacterial meningitis, now that an effective Hib vaccine is in use. Most of the cases of pneumococcal meningitis occur among children between the ages of 1 month and 4 years For a bacterial disease, the mortality rate is high: about 8% in children and 22% in the elderly A conjugated vaccine, modeled after the Hib vaccine, is recommended for infants under the age of 2

sugar and cavities

Studies have shown that sucrose, a disaccharide composed of glucose and fructose, is much more cariogenic than either glucose or fructose individually high-starch diets (starch is a polysaccharide of glucose) have a low incidence of tooth decay unless sucrose is also a significant part of their diet The contribution of bacteria to tooth decay has been shown by experiments with germ-free animals. Such animals don't develop caries even when fed a sucrose-rich diet designed to encourage their formation Sugar alcohols, such as mannitol, sorbitol, and xylitol, are not cariogenic; xylitol even appears to inhibit carbohydrate metabolism in S. mutans. This is why these sugar alcohols are used to sweeten "sugarless" candies and chewing gum.

chancroid (soft chancre)

The STI known as chancroid (soft chancre) occurs most frequently in tropical areas, where it is seen more often than syphilis Like syphilis, chancroid is a risk factor in the transmission and acquisition of HIV infection a swollen, painful ulcer that forms on the genitals involves an infection of the adjacent lymph nodes. Infected lymph nodes in the groin area sometimes even break through and discharge pus to the surface. Such lesions are an important factor in the sexual transmission of HIV, especially in Africa Lesions might also occur on such diverse areas as the tongue and lips. The causative agent is Haemophilus ducreyi, a small gram-negative rod that can be isolated from exudates of lesions Symptoms and the culture of these bacteria are the primary means of diagnosis recommended antibiotics include single doses of azithromycin or ceftriaxone

Salmonella (Salmonella gastroenteritis)

The Salmonella bacteria are gram-negative, facultatively anaerobic rods. normal habitat is the intestinal tracts of humans and many animals All salmonellae are considered pathogenic to some degree, causing salmonellosis, or Salmonella gastroenteritis Pathogenically, salmonellae are separated into typhoidal salmonellae and the nontyphoidal salmonellae, which cause the milder disease of salmonellosis The nomenclature of the Salmonella microbes differs from the norm. There are only two species: S. enterica and S. bongori. Infections are most often caused by S. enterica. There are more than 2000 serotypes (or serovars), of S. enterica, only about 50 of which are isolated with any frequency in the United States. The salmonellae first invade the intestinal mucosa and multiply there; Occasionally manage to pass the intestinal mucosa at M cells to enter the lymphatic and cardiovascular systems, and from there they may spread and eventually affect many organs They replicate readily within macrophages. Salmonellosis has an incubation time of about 12 to 36 hours. There is usually a moderate fever accompanied by nausea, abdominal pain and cramps, and diarrhea. Antibiotic therapy isn't useful in treating salmonellosis or, indeed, many diarrheal diseases; treatment consists of oral rehydration therapy The bacteria have developed the ability to survive in the albumin, which contains natural preservatives such as lysozyme and lactoferrin (which binds iron the bacteria require). Estimates are that 1 in 20,000 eggs in this country is contaminated by Salmonella.

Trichomoniasis

The anaerobic protozoan Trichomonas vaginalis is frequently a normal inhabitant of the vagina in women and of the urethra in many men It's usually sexually transmitted. If the normal acidity of the vagina is disturbed, the protozoan may overgrow the normal microbial population of the genital mucosa and cause trichomoniasis. (Men rarely have any symptoms resulting from the presence of the protozoan.) often accompanied by a coinfection with gonorrhea. In response to the protozoan infection, the body accumulates leukocytes at the infection site. The resulting discharge is profuse, greenish yellow, and characterized by a foul odor. This discharge is accompanied by irritation and itching. Up to half the cases, however, are asymptomatic. The incidence of trichomoniasis is higher than that of gonorrhea or chlamydia, but it is considered relatively benign and is not a reportable disease Diagnosis is usually made by microscopic examination and identification of the organisms in the discharge. They can also be isolated and grown on laboratory media The pathogen can be found in semen or urine of male carriers New rapid tests making use of DNA probes and monoclonal antibodies are now available. Treatment is by oral metronidazole, administered to both sex partners, which readily clears the infection

Treatment of Influenza

The antiviral drugs zanamivir and oseltamivir significantly reduce the symptoms of influenza A if administered promptly are inhibitors of neuraminidase. If taken within 24 hours of onset of influenza, these drugs slow replication This action allows the immune system to be more effective, which shortens durations of symptoms and lowers the mortality rate The bacterial complications of influenza are amenable to treatment with antibiotics

Candidiasis

The bacterial microbiota of the mucous membranes in the genitourinary tract and mouth usually suppress the growth of such fungi as Candida albicans Several other species of Candida, for example C. tropicalis or C. krusei may also be involved morphology of these organisms is not always yeastlike but can exhibit the formation of pseudohyphae, long cells that resemble hyphae. In this form, Candida is resistant to phagocytosis Bc the fungus is not affected by antibacterial drugs, it sometimes overgrows mucosal tissue when antibiotics suppress the normal bacterial microbiota. Changes in the normal mucosal pH may have a similar effect. Such overgrowths by C. albicans are called candidiasis. Newborn infants, whose normal microbiota have not become established, often suffer from a whitish overgrowth of the oral cavity, called thrush C. albicans is also a very common cause of vaginitis Immunosuppressed individuals, including AIDS patients, are unusually prone to Candida infections of the skin and mucous membranes On people who are obese or diabetic, the areas of the skin with more moisture tend to become infected with this fungus. The infected areas become bright red, with lesions on the borders Skin and mucosal infections by C. albicans are usually treated with topical applications of miconazole, clotrimazole, or nystatin If candidiasis becomes systemic, as can happen in immunosuppressed individuals, fulminating disease (one that appears suddenly and severely) and death can result drug of choice to treat systemic candidiasis is fluconazole

syphilis

The causative agent of syphilis is a gram-negative spirochete, Treponema pallidum. Thin and tightly coiled, T. pallidum stains poorly with the usual bacterial stains it lacks the enzymes necessary to build many complex molecules; therefore, it relies on the host for many of the compounds necessary for life Outside the mammalian host, the organism loses infectiveness within a short time grow slowly in rabbits, with a generation time of 30 hours or more. They can be grown in cell culture, at low oxygen concentrations, but only for a few generations. T. pallidum has no obvious virulence factors such as toxins, but it produces several lipoproteins that induce an inflammatory immune response. This is what apparently causes the tissue destruction of the disease Almost immediately on infection, the organisms rapidly enter the bloodstream and invade deeper tissues, easily crossing the junctions between cells. have a corkscrew-like motility that allows them to swim readily in gel-like tissue fluids Separate strains of T. pallidum (subspecies T.p. pertenue) are responsible for certain tropically endemic skin diseases such as yaws. These cause skin lesions but are not sexually transmitted. Syphilis is transmitted by sexual contact of all kinds via syphilitic infections of the genitals or other body parts incubation period averages 3 weeks but can range from 2 weeks to several months The disease progresses through several recognized stages

disease cryptococcosis

The disease cryptococcosis is caused by fungi of the genus Cryptococcus. They form spherical cells resembling yeasts, reproduce by budding, and produce extremely heavy polysaccharide capsules (Figure 22.15). The primary species pathogenic for humans are Cryptococcus neoformans and C. grubii. These organisms are widely distributed, especially in areas contaminated by bird droppings most notably from pigeons, which excrete an estimated 25 pounds a year. The disease is transmitted mainly by the inhalation of dried, contaminated droppings. The inhaled fungi multiply in persons with compromised immune systems, such as AIDS patients, disseminate to the CNS, and cause meningitis that has a high mortality rate. In recent years there have been outbreaks of cryptococcosis in AIDS patients in California caused by C. gattii (GAHT-te¯-e¯), a species that had previously been reported only in tropical regions. However, an association has now been observed with trees native to subtropical and temperate regions, as well; the fungus inhabits an ecological niche in decayed hollows of mature trees. See the Clinical Case on page 325. From there the basidiospores (see page 330) can contaminate surrounding soils or be spread with the distribution of wood products. This species has now been isolated in cases of cryptococcosis, even in otherwise healthy individuals, in several areas of western North America as far north as Vancouver Island in Canada. This disease is likely to continue to spread southward and may eventually affect areas as far as Florida. The best serological diagnostic test is a latex agglutination test to detect cryptococcal antigens in serum or cerebrospinal fluid. The drugs of choice for treatment are amphotericin B and flucytosine in combination. Even so, the mortality rate may approach 30%.

Bacteria and cavities

The dominant microorganisms are gram-positive rods and filamentous bacteria; S. mutans is present in small numbers Although once considered the cause of dental caries, Lactobacillus spp. actually play no role in initiating the process. However, these very prolific lactic acid producers are important in advancing the front of the decay once it has become established.

Treatment of Tuberculosis

The first effective antibiotic for TB treatment was streptomycin, which was introduced in 1944. Streptomycin is still in use, and all of the currently used drugs were developed decades ago Even the short course of treatment for TB (there are variations in the regimen, depending on sensitivity of the organism and other factors) requires the patient to adhere to a minimum of 6 months of therapy Multiple-drug therapy is needed to minimize the emergence of resistant strains. This typically includes four drugs, isoniazid, rifampin, ethambutol, and pyrazinamide, which are considered first-line drugs If the strain of M. tuberculosis is susceptible to the drugs, this regimen can lead to a cure. The likelihood that resistance may develop is increased because many patients fail to faithfully follow such a prolonged regimen, which can involve 130 doses of the drugs number of second-line drugs that can be used, mainly if resistance develops to alternatives. These include several aminoglycosides, fluoroquinolones, streptomycin, and para-aminosalicylic acid (PAS). 2md class drugs either less effective than first-line drugs, have toxic side effects, or may be unavailable in some countries prolonged treatment necessary bc the tubercle bacillus grows very slowly or is only dormant (the only drug effective against the dormant bacillus is pyrazinamide), and many antibiotics are effective only against growing cells. Also, the bacillus may be hidden for long periods in macrophages or other locations that are difficult to reach with antibiotics. TB that are caused by multi-drug-resistant (MDR) strains. These are defined as being resistant to the two most effective first-line drugs, isoniazid and rifampin. These cases, defined as extensively drug-resistant (XDR), are virtually untreatable and are emerging globally(no 1st or 2nd treatment) 30-90% of persons with TB are also HIV positive—with the accompanying damage to the immune system In one study, all patients testing positive for both HIV and XDR tuberculosis died within 3 months of diagnosis

Treatment of Gonorrhea

The guidelines for treating gonorrhea require constant revision as resistance appears Bc of increasing multi-drug resistance, the only recommended treatment for all forms of gonorrhea (cervical, urethral, rectal, pharyngeal) is 250 mg of ceftrixone and 1 g azithromycin Unless a coinfection by Chlamydia trachomatis can be ruled out, the patient should also be treated for this organism It's also standard practice to treat sex partners of patients to decrease the risk of reinfection and to decrease the incidence of STIs in general.

Hepatitis A

The hepatitis A virus (HAV) is the causative agent of hepatitis A. The virus contains single-stranded RNA and lacks an envelope. It can be grown in cell culture. After a typical entrance via the oral route, HAV multiplies in the epithelial lining of the intestinal tract. Viremia eventually occurs, and the virus spreads to the liver, kidneys, and spleen. The virus is shed in the feces and can also be detected in the blood and urine. The amount of virus excreted is greatest before symptoms appear and then declines rapidly. Therefore, a food handler responsible for spreading the virus might not appear to be ill at the time. The virus can probably survive for several days on such surfaces as cutting boards. HAV is resistant to chlorine disinfectants at concentrations ordinarily used in water, a characteristic that enhances fecal contamination of food or drink. Mollusks, such as oysters, that live in contaminated waters are also a source of infection. At least 50% of infections with HAV are subclinical, especially in children. In clinical cases, the initial symptoms are anorexia (loss of appetite), malaise, nausea, diarrhea, abdominal discomfort, fever, and chills. These symptoms are more likely to appear in adults; they last 2 to 21 days, and the mortality rate is low. Nationwide epidemics occur about every 10 years, mostly in people under 14. In some cases, there is also jaundice (signs are yellowing of the skin and the whites of the eyes) and the dark urine typical of liver infections. In these cases, the liver becomes tender and enlarged. There is no chronic form of hepatitis A, and the virus is usually shed only during the acute stage of disease. The incubation time averages 4 weeks and ranges from 2 to 6 weeks, making epidemiological studies for the source of infections difficult. There are no animal reservoirs. Acute disease is diagnosed by the detection of IgM anti-HAV because these antibodies appear about 4 weeks after infection and disappear about 3 to 4 months after infection. Recovery results in lifelong immunity. No specific treatment for the disease exists, but people at risk of exposure or who have been exposed to hepatitis A can be given immune globulin, which provides protection for several months. Inactivated vaccines are recommended for travelers to areas of endemic disease and for high-risk groups, such as homosexual men and injecting street-drug users (IDUs). HAV vaccination is now part of the recommended childhood vaccination schedule. The annual number of reported cases has declined from 30,000, before the vaccine, to 1800 in 2006.

infectious mononucleosis

The identification of EB virus as the cause of infectious mononucleosis, or mono infection characterized by fever, sore throat, swollen lymph nodes in the neck, and general weakness. now tested serologically positive for EB virus the same virus that is associated with Burkitt's lymphoma also causes almost all cases of infectious mononucleosis Nearly 20% of adults in the United States carry EB virus in oral secretions. Childhood EB virus infections are usually asymptomatic, but if infection is delayed until young adulthood, as is often the case in the United States, the result is more symptomatic probably because of an intense immunological response cause of the rare deaths is rupture of the enlarged spleen (a common response to a systemic infection) during vigorous activity Recovery usually complete in a few weeks, and immunity is permanent. The usual route of infection is by the transfer of saliva by kissing or, for example, by sharing drinking vessels It doesn't spread among casual household contacts, so aerosol transmission is unlikely The incubation period before appearance of symptoms is 4 to 7 weeks EB virus maintains a persistent infection in the mouth and throat, which accounts for its presence in saliva. It is probable that resting memory B cells located in lymphoid tissue are the primary site of replication and persistence Most of the symptoms are attributed to responses of T cells to the infection The disease name mononucleosis refers to lymphocytes with unusual lobed nuclei that proliferate in the blood during the acute infection The infected B cells produce heterophile antibodies, so called from the Greek hetero (different) and phile (affinity). These are weak antibodies with multispecific activities; their significance is that they are used in the diagnosis of mono. If this test is negative, the symptoms may be caused by cytomegalovirus or several other disease conditions A fluorescent-antibody test that detects IgM antibodies against EB virus is the most specific diagnostic method. There is no recommended therapy for most patients.

Malaria Vaccines

The malarial parasite reproduces in a series of stages. The number of parasites that would serve as targets for a vaccine vary greatly in these stages sporozoite stage involves few pathogens and was an early target for experimental vaccines. In the liver stage, the vaccine would need to deal with hundreds of pathogens. Once the parasite begins to proliferate in the blood, the numbers quickly reach into the trillions. Vaccines targeting this stage are likely only to moderate symptoms transmission-blocking vaccine. The idea is to use the human host to generate antibodies and deliver them to the biting mosquito. There, instead of dealing with trillions of parasites, the vaccine needs to deal only with the relative handful in the mosquito. Obviously, the disadvantage is that the recipients of the vaccine still get sick but would have the questionable satisfaction of knowing they are not likely to be passing it on to someone else special problems in developing a malarial vaccine. For example, in its various stages, the pathogen has as many as 7000 genes that can mutate. The result is that the parasite is very efficient at evading the human immune response One such vaccine, made from a sporozoite protein produced in yeast, will be tested in three countries in 2017 to determine whether the clinical trial results can be replicated in real life.

Chlamydia trachomatis

The most common pathogen associated with NGU is Chlamydia trachomatis Many people suffering from gonorrhea are coinfected with C. trachomatis, which infects the same columnar epithelial cells as the gonococcus. C. trachomatis is also responsible for the STI lymphogranuloma venereum twice as many cases are reported in women as in men. In women, it is responsible for many cases of pelvic inflammatory disease, plus eye infections and pneumonia in infants born to infected mothers. Untreated genital chlamydial infections are also associated with an increased risk of cervical cancer. Chlamydia-infected cells may be more susceptible to infection with human papillomavirus Bc the symptoms are often mild in men and because women are usually asymptomatic, many cases of NGU go untreated Although complications are not common, they can be serious. Men may develop inflammation of the epididymis In women, inflammation of the uterine tubes may cause scarring, leading to sterility. As many as 60% of such cases may be from chlamydial rather than gonococcal infection. It's estimated that about 50% of men and 70% of women are unaware of their chlamydial infection NAATs are the most reliable methods of diagnosis, and they can be done quickly. Urine samples can be used, but the sensitivity is lower than with swabs. Swab specimens (urethral or vaginal, as the case might be) collected by the patients themselves are often used Bacteria other than C. trachomatis can also be implicated in NGU. Mycoplasma genitalium causes up to 30% of urethritis cases in males. This bacterium may cause cervicitis in women Another cause of urethritis is Ureaplasma urealyticum This pathogen is a member of the mycoplasma (bacteria without a cell wall). Both chlamydia and mycoplasma are sensitive to azithromycin and doxycyline

inhalational (pulmonary) anthrax

The most dangerous form of anthrax in humans is inhalational (pulmonary) anthrax. Endospores inhaled into the lungs have a high probability of entering the bloodstream. Symptoms of the first few days of the infection are not especially alarming: mild fever, coughing, and some chest pain. Antibiotics can arrest the disease at this stage, but unless suspicion of anthrax is high, they are unlikely to be administered. As the bacteria enter the bloodstream and proliferate, the illness progresses in 2 or 3 days into septic shock that usually kills the patient within 24 to 36 hours. The mortality rate is exceptionally high, approaching 100%

typhoid fever

The most virulent serotype of Salmonella, S. Typhi, causes the bacterial disease typhoid fever. this pathogen is not found in animals; it's spread only in the feces of other humans still a frequent cause of death in parts of the world with poor sanitation. Globally, an estimated 21 million cases occur annually, causing tens of thousands of deaths Instead of being destroyed by phagocytic cells, S. Typhi multiply within them and are disseminated into multiple organs, especially the spleen and liver. Eventually, the phagocytic cells lyse and release S. Typhi into the bloodstream; time required for this explains why the incubation period of typhoid fever (2 or 3 weeks) is much longer than for salmonellosis (12 to 36 hours) suffers from a high fever of about 40°C and continual headache. Diarrhea appears only during the second or third week, and the fever then tends to decline In severe cases, which can be fatal, ulceration and perforation of the intestinal wall can occur. 1-3%, become chronic carriers. They harbor the pathogen in the gallbladder and continue to shed bacteria for several months. A number of such carriers continue to shed the organism indefinitely When the antibiotic chloramphenicol was introduced in 1948, typhoid became a treatable disease. However, chloramphenicol-resistant Salmonella emerged in the 1970s, and ceftriaxone or azithromycin is now largely used instead Treatment of the chronic carrier might require weeks of antibiotic therapy Recovery from typhoid confers lifelong immunity.

Mycoplasmal Pneumonia

The mycoplasmas, which do not have cell walls, do not grow under the conditions normally used to recover most bacterial pathogens pneumonias caused by mycoplasmas are often confused with viral pneumonias bacterium Mycoplasma pneumoniae is the causative agent of mycoplasmal pneumonia common type of pneumonia in young adults and children. It may account for as much as 20% of pneumonias, although it is not a reportable disease. The symptoms, which persist for 3 weeks or longer, are low-grade fever, cough, and headache. Occasionally, they are severe enough to lead to hospitalization Other terms for the disease are primary atypical (that is, the most common pneumonia not caused by the pneumococcus) and walking pneumonia When isolates from throat swabs and sputum grow on a medium containing horse serum and yeast extract, some form distinctive colonies with a "fried-egg" appearance The colonies are so small that they must be observed with magnification. The mycoplasmas are highly varied in appearance because they lack cell walls Diagnosis based on recovering the pathogens might not be useful in treatment because as long as 3 or more weeks may be required for the slow-growing organisms to develop Rapid PCR tests are becoming available; however, they are expensive and have not been clinically validated Treatment with antibiotics such as tetracycline usually hastens the disappearance of symptoms but does not eliminate the bacteria, which the patient continues to carry for several weeks.

protozoan STIs

The only STI caused by a protozoan affects mostly young, sexually active women may be the most common STI—nearly 8 million cases per year are reported in the United States—but it isn't widely known. Its prevalence in certain STI clinics is 25% or higher

Mumps

The targets of the mumps virus, the parotid glands, are located just below and in front of the ears (see Figure 25.1). Because the parotids are one of the three pairs of salivary glands of the digestive system, it is appropriate to include a discussion of mumps in this chapter. Mumps typically begins with painful swelling of one or both parotid glands 16 to 18 days after exposure to the virus (Figure 25.13). The virus is transmitted in saliva and respiratory secretions, and its portal of entry is the respiratory tract. An infected person is most infective to others during the first 48 hours before clinical symptoms appear. Once the viruses have begun to multiply in the respiratory tract and local lymph nodes in the neck, they reach the salivary glands via the blood. Viremia (the presence of virus in the blood) begins several days before the onset of mumps symptoms and before the virus appears in saliva. The virus is present in the blood and saliva for 3 to 5 days after the onset of the disease and in the urine after about 10 days. Mumps is characterized by inflammation and swelling of the parotid glands, fever, and pain during swallowing. About 4 to 7 days after the onset of symptoms, the testes can become inflamed, a condition called orchitis. This happens in about 20-40% of men past puberty; sterility is a possible but rare consequence. Other possible complications include meningitis, inflammation of the ovaries, and pancreatitis. An effective attenuated live vaccine is available and is often administered as part of the trivalent measles, mumps, rubella (MMR) vaccine. Second attacks are rare, and cases involving only one parotid gland or subclinical cases (about 15-20% of those infected), are as effective as bilateral mumps in conferring immunity. If confirmation of the diagnosis (which usually is based only on symptoms) is desired, the virus can be isolated by embryonated egg or cell culture techniques and identified by ELISA tests.

bacterial pneumonia

The term pneumonia is applied to many pulmonary infections, most of which are caused by bacteria. Pneumonia caused by Streptococcus pneumoniae is the most common, about two-thirds of cases, and is therefore referred to as typical pneumonia. Pneumonias caused by other microorganisms, which can include fungi, protozoa, viruses, and other bacteria, especially mycoplasma, are termed atypical pneumonias This distinction is becoming increasingly blurred in practice. Pneumonias also are named after the portions of the lower respiratory tract they affect For example, if the lobes of the lungs are infected, it is called lobar pneumonia; pneumonias caused by S. pneumoniae are usually of this type. Bronchopneumonia indicates that the alveoli of the lungs adjacent to the bronchi are infected Pleurisy is often a complication of various pneumonias, in which the pleural membranes become painfully inflamed.

Leprosy: Tuberculoid (neural) form

The tuberculoid (neural) form is characterized by discolored regions of the skin that have lost sensation and may be surrounded by a border of nodules This disease form is roughly the same as paucibacillary in the WHO leprosy classification system Tuberculoid disease occurs in people with effective immune reactions. Recovery sometimes occurs spontaneously

Typhus

The various typhus diseases are caused by rickettsias, bacteria that are obligate intracellular parasites of eukaryotes Rickettsias, which are spread by arthropod vectors, infect mostly the endothelial cells of the vascular system and multiply within them The resulting inflammation causes local blockage and rupture of the small blood vessels.

amebic meningoencephalitis

There are three species of free-living protozoa that cause amebic meningoencephalitis, a devastating disease of the nervous system. These protozoa are both found in recreational freshwater. Human exposure to them is apparently widespread; many in the population carry antibodies—fortunately, symptomatic disease is rare. Naegleria fowleri is a protozoan (ameba) that causes a neurological disease, primary amebic meningoencephalitis. The most common victims are children who swim in warm ponds or streams. The organism initially infects the nasal mucosa and later penetrates to the brain and proliferates, feeding on brain tissue. The fatality rate is nearly 100%, death occurring within a few days after symptoms appear. Because of the rarity of the disease, there is a low "index of suspicion"; also, the symptoms resemble those of encephalitis caused by other, more common, pathogens. Diagnosis is typically made at autopsy. There have been only a very few survivors of PAM. They were treated with a combination of several antibiotics. A similar neurological disease is granulomatous amebic encephalitis (GAE). GAE is caused by Acanthamoeba spp. It is chronic, slowly progressive, and fatal in a matter of weeks or months. GAE has an unknown incubation period, and months may elapse before symptoms appear. Granulomas form around the organism in response to an immune reaction. The portal of entry is not known but is probably mucous membranes. Multiple lesions are formed in the brain and other organs, especially the lungs mandrillaris is a free-living ameba that causes GAE in mammals. The ameba, present in soil, is probably transmitted by inhalation or through skin lesions. Approximately 150 cases of balamuthiasis have been reported worldwide since the disease was recognized in 1990; 10 of those cases were in the United States. Of the 150 people affected, only 7 survived. Miltefosine is available from the CDC to treat infections caused by N. fowleri, Acanthamoeba spp., and B. mandrillaris.

Therapy for malaria

There is a lengthy list of antimalarial drugs available; In the United States, if the species cannot be identified it should be assumed that the patient is infected with P. falciparum. If the patient is from an area still sensitive to chloroquine, it is the drug of choice for patients coming from chloroquine-resistant zones, there are several options. The two currently preferred are malarone or oral quinine plus an antibiotic such as doxycycline. The WHO recommends artemisinin combination therapies (ACT) for treatment of malaria worldwide. They are not used for prophylaxis. Examples of artemisinin derivatives are artesunate (not licensed in the United States) and artemether The short-lived artemisinin component of ACT is intended to remove most of the parasites; the partner drug, with an extended period of activity, is intended to eliminate the remainder As with other tropical diseases, the availability of medications is limited by the very low income of the people affected, which makes their development unprofitable most profitable application of antimalarials will probably continue to be prophylaxis of travelers to malarial areas.

Vaccines for polio

There is no cure for polio; it can only be prevented. There are three different serotypes of the poliovirus: types 1, 2, and 3. Immunity must be provided for all three Two different vaccine types are available. In 1955, the Salk vaccine (named after Jonas Salk, its developer) was introduced. It consists of viruses of all three types that have been inactivated (killed) by treatment with formalin. Vaccines of this types, called inactivated polio vaccines (IPV), require a series of injections. A version with enhanced potency in 1988. The other vaccine type, introduced in 1963, contains living, attenuated (weakened) strains of the virus in a suspension that is ingested. This Sabin vaccine, named after its developer (Albert Sabin), is more commonly called oral polio vaccine (OPV). It usually contains the three types of polio virus (trivalent, tOPV). It is less expensive to manufacture and is simpler to administer because it does not require the trained personnel and equipment needed for safe, sterile injections. This vaccine mimics an actual infection and induces excellent, and probably life-long, immunity, although its use is precluded in immunodeficient individuals. The live virus is also shed by the recipient and has the effect of immunizing others within the community. shedding can represent a serious disadvantage—the attenuated strains of the disease occasionally revert to virulence and cause the disease

Endemic Murine Typhus

Transmitted by the rat flea Xenopsylla cheopis endemic murine typhus occurs sporadically rather than in epidemics The term murine (derived from Latin for mouse) refers to the fact that rodents, such as rats and squirrels, are the common hosts for this type of typhus responsible for the disease is Rickettsia typhi, a common inhabitant of rats. With a mortality rate of less than 5%, the disease is considerably less severe than typhus fever. Except for the reduced severity of the disease, endemic murine typhus is clinically indistinguishable from typhus fever Tetracycline and chloramphenicol are effective treatments for endemic murine typhus, and rat control is the best preventive measure

Botulinal Types

Type A toxin is probably the most virulent. Deaths have resulted from type A toxin when the food was only tasted but not swallowed. It is even possible to absorb lethal doses through skin breaks while handling laboratory samples in untreated cases, the mortality rate is 60-70%. The type A endospore is the most heat resistant of all C. botulinum strains. In the United States, it is found mainly in California, Washington, Colorado, Oregon, and New Mexico The type A organism is usually proteolytic (the breakdown of proteins by clostridia releases amines with unpleasant odors), but obvious spoilage odor is not always apparent in lowprotein foods, such as corn and green beans Type B toxin is responsible for most European outbreaks of botulism and is the most common type in the eastern United States The mortality rate in cases without treatment is about 25%. Type B botulism organisms occur in both proteolytic and nonproteolytic strains Type E toxin is produced by botulism organisms that are often found in marine or lake sediments. Therefore, outbreaks commonly involve seafood and are especially common in the Pacific Northwest, Alaska, and the Great Lakes area, endospore of type E botulism is less heat resistant than that of other strains and is usually destroyed by boiling. Type E is nonproteolytic, so the chance of detecting spoilage by odor in highprotein foods such as fish is minimal. The pathogen is also capable of producing toxin at refrigerator temperatures and requires less strictly anaerobic conditions for growth.

Typhus Fever (Epidemic Louseborne Typhus)

Typhus fever is caused by Rickettsia prowazekii and is carried by the human body louse Pediculus humanus corporis The pathogen grows in the gastrointestinal tract of the louse and is excreted by it. It is transmitted when the feces of the louse are rubbed into the wound when the bitten host scratches the bite The disease flourishes in crowded and unsanitary surroundings, when lice can transfer readily from an infected host to a new host. Although a rare disease in the United States, several cases have occurred in the eastern states from contact with flying squirrels or their nests Typhus fever produces a high and prolonged fever that lasts at least 2 weeks. Stupor and a rash of small red spots caused by subcutaneous hemorrhaging are characteristic, as the rickettsias invade blood vessel linings Mortality rates are very high when the disease is untreated. Tetracycline and chloramphenicol are usually effective against typhus fever, but eliminating conditions in which the disease flourishes is more important microbe is considered especially hazardous, and attempts to culture it require extreme care Vaccines are available for military populations, which historically have been highly susceptible to the disease

Urithritis

Urinary system infections are most frequently initiated by an inflammation of the urethra, or urethritis. Infection of the urinary bladder is called cystitis, and infection of the ureters is ureteritis most significant danger from lower urinary tract infections is that they may move up the ureters and affect the kidneys, causing pyelonephritis. Occasionally the kidneys are affected by systemic bacterial diseases, such as leptospirosis. The pathogens causing these diseases are found in excreted urine. Bacterial infections of the urinary system are usually caused by microbes that enter the system from external sources Bc of the proximity of the anus to the urinary opening, intestinal bacteria predominate in urinary tract infections. Most infections of the urinary tract are caused by Escherichia coli Infections by Pseudomonas, because of their natural resistance to antibiotics, are troublesome.

candidiasis infections

Vaginal infections by yeastlike fungi of the genus Candida are responsible for millions of physician office visits every year. By the time they reach the age of 25, an estimated half of college women will have had at least one physician-diagnosed episode. Nonprescription antifungal therapies to treat these infections are among the best-selling over-the-counter products in the United States. Candida albicans is the most common species, causing 85-90% of cases. Infections by other species, such as C. glabrata, are more likely to be resistant to antifungals and to be chronic or recurrent. C. albicans often grows on mucous membranes of the mouth, intestinal tract, and genitourinary tract (see Diseases in Focus 26.2; see also Figure 21.17, page 609). Infections are usually a result of opportunistic overgrowth when the competing microbiota are suppressed by antibiotics or other factors. C. albicans is the cause of oral candidiasis, or thrush (see Chapter 21, page 609). It's also responsible for occasional cases of NGU in men and for vulvovaginal candidiasis, which is the most common cause of vaginitis. About 75% of all women experience at least one episode. The lesions of vulvovaginal candidiasis resemble those of thrush but produce more irritation: severe itching; a thick, 779 yellow, cheesy discharge; and yeasty or no odor. C. albicans, the Candida species responsible for most cases, is an opportunistic pathogen. Predisposing conditions include the use of oral contraceptives and pregnancy, which cause an increase of glycogen in the vagina (see the discussion of the normal vaginal microbiota on page 762). Hormones are probably a factor; candidiasis is much less common in girls before puberty or in women after menopause. Yeast infections are a frequent symptom in women suffering from uncontrolled diabetes. Thus, diabetes and antibiotic therapy are predisposing factors to C. albicans vaginitis. A yeast infection is diagnosed by microscopic identification of the fungus in scrapings of lesions and by isolation of the fungus in culture. Treatment usually consists of topical application of nonprescription antifungal drugs such as clotrimazole and miconazole. An alternative treatment is a single dose of oral fluconazole or other azole-type antifungal.

genital warts

Warts are an infectious disease caused by viruses known as papillomaviruses Many papillomaviruses have a predilection for growth not on the skin, but on the mucous membranes that line organs such as the respiratory tract, mouth, anus, and genitalia. Such genital warts (or condyloma acuminata) are usually transmitted sexually and are an increasing problem more than 60 types of human papillomaviruses (HPV), and certain serotypes tend to be linked with certain forms of genital warts Penile lesions are often flat and quite inapparent, an important factor in male to female transmission. The incubation period is usually a matter of a few weeks or months. Visible genital warts are most often caused by serotypes 6 and 11. These serotypes rarely cause cancer, which is the most serious concern with these infections The types most likely to cause cancer are types 16 and 18, but these have a relatively low prevalence. Even so, cervical cancer caused by HPV kills at least 4000 women annually in the United States Oral, anal, and penile cancers are also attributed to HPV infections. The quadrivalent HPV vaccine protects against infection by HPV types 6, 11, 16, and 18. The more expensive nine-valent vaccine protects against the four HPVs in the quadrivalent vaccine plus serotypes 31, 33, 45, 52, and 58 The vaccines are recommended for adolescents aged 11 through 12 years and are even required in some areas The immune response to the vaccines is much more effective than that resulting from a natural infection, which is relatively weak Warts can be treated but not cured, but approximately 90% of cases clear spontaneously within 2 years The available methods used for warts, such as surgery or cryotherapy, are not as effective against genital warts. Two patient-applied gels, podofilox and imiquimod, are often useful treatments. Imiquimod stimulates the body to produce interferon, which appears to account for its antiviral activity

Warts

Warts, or papillomas, are generally benign skin growths caused by viruses. It was long known that warts can be transmitted from one person to another by contact, even sexually, but it was not until 1949 that viruses were identified in wart tissues. More than 50 types of papillomavirus are now known to cause different kinds of warts, often with greatly varying appearances. After infection, there is an incubation period of several weeks before the warts appear. The most common medical treatments for warts are to apply extremely cold liquid nitrogen (cryotherapy), dry them with an electrical current (electrodesiccation), or burn them with acids. There is evidence that compounds containing salicylic acids are especially effective. Topical application of prescription drugs such as podofilox, which inhibits cell division, or imiquimod, which activates toll-like receptors (page 448), is often effective. Warts that do not respond to any other treatments can be treated with lasers or injected with bleomycin, an antitumor drug. Although warts are not a form of cancer, some skin and cervical cancers are associated with certain papillomaviruses. Genital warts is the most common sexually transmitted infection (Chapter 26, page 778).

Whipworm (Trichuris trichiura)

Whipworm infestations, known as trichuriasis, are widespread in tropical areas of the world, especially Asia worms are 30 to 50 mm in length. The main body is thin and hairlike, but the posterior end abruptly becomes thick, resembling a coiled whip with a handle distribution and incidence are similar to those of A. lumbricoides. Medical technicians microscopically inspecting fecal samples will occasionally encounter the whipworm's distinctive egg Nationally, eggs are present in a little over 1% of the population. In southeastern states, children pick up infective eggs from contaminated soil; in that area of the United States, the incidence of whipworm in children is about 20%. When an embryonated egg is ingested, it hatches and enters the intestinal glands. There the worm grows and slowly begins to tunnel back to the interior intestinal surface. Eventually, the worm positions itself such that the posterior end extends into the intestinal lumen and the hairlike anterior remains buried in the mucosa worm lives there for several years as a tissue parasite, feeding on cell contents and blood. Light infections of fewer than 100 worms usually pass unnoticed, but very heavy infestations may cause abdominal pain and diarrhea Trichuriasis can also lead to anemia and malnutrition, resulting in significant weight loss and retarded growth Treatment is with mebendazole or albendazole, most cases do not require medical attention.

Brucellosis (Undulant Fever)

With over 500,000 new human cases annually, brucellosis is the world's most common bacterial zoonosis. It is endemic in the Mediterranean Basin, South and Central America, Eastern Europe, Asia, Africa, and the Middle East. It is also economically important as a disease of animals in the developing world Human cases of brucellosis are usually not fatal, but the disease tends to persist in the reticuloendothelial system, where the bacteria evade the host's defenses; they are especially adept at evading phagocytic cells. This ability allows long-term survival and replication. T often becomes chronic and is capable of affecting any organ system. Brucella bacteria are small, aerobic, gram-negative coccobacilli. During laboratory handling, they easily become airborne and are considered dangerous to handle. In fact, they are considered a potential agent of bioterrorism There are three species of Brucella bacteria that are of greatest interest. Brucella abortus is found primarily in cattle but also infects camels, bison, and several other animals. Brucella suis is a species mostly infecting swine but is known to infect cattle when they are kept in contact with swine herds. Abattoir (slaughterhouse) workers who come in contact with swine carcasses are at risk of brucellosis from this species The most serious pathogen, and the cause of most human cases, is Brucella melitensis. This species is most commonly found today in goats and sheep most U.S. cases of brucellosis are caused by B. melitensis, predominantly among Hispanics. The disease is endemic in Mexico and is often imported into the United States in unpasteurized food products, such as Mexican soft cheese made from goat milk The incubation period is usually 1 to 3 weeks but might be much longer. Symptoms of brucellosis have a wide spectrum, depending on the stage of the disease and the organs affected Typically they include fever (often rising and falling, which has given the disease an alternative name of undulant fever), malaise, night sweats, and muscle aches Although several serological tests are available, there is still a need for a definitive diagnostic test. The ultimate diagnostic proof is isolation of Brucella from the patient's blood or tissue. Because the disease is not common, diagnosis often must start with patient interviews that suggest a contact in endemic areas of the disease Antibiotic therapy is possible, and the bacteria have not shown development of resistance. However, treatment must be very long term, usually at least 6 weeks, and involves a combination of at least two antibiotics

Infections by Pseudomonads

aerobic gram-negative rods that are widespread in soil and water. Capable of surviving in any moist environment, they can grow on traces of unusual organic matter, such as soap films or cap liner adhesives used for many product containers resistant to many antibiotics and disinfectants. The most prominent species is Pseudomonas aeruginosa, which is considered the model of an opportunistic pathogen frequently cause outbreaks of Pseudomonas dermatitis. This is a self-limiting rash of about 2 weeks' duration, often associated with swimming pools and pool-type saunas and hot tubs. When many people use these facilities the alkalinity rises, and the chlorines become less effective; at the same time, the concentration of nutrients that support the growth of pseudomonads increases. Hot water causes hair follicles to open wider, facilitating the entry of bacteria. otitis externa, or "swimmer's ear," a painful infection of the external ear canal leading to the eardrum that is frequently caused by pseudomonads. P. aeruginosa produces several exotoxins that account for much of its pathogenicity. It also produces an endotoxin. P. aeruginosa often grows in dense biofilms that contribute to its frequent identification as a cause of healthcare-associated infections of indwelling medical tubes or devices serious opportunistic pathogen for patients with the genetic lung disease cystic fibrosis; biofilm formation plays a prominent part in this. P. aeruginosa is also a very common and serious opportunistic pathogen in burn patients, particularly those with second- and third-degree burns. Infection may produce bluegreen pus, whose color is caused by the bacterial pigment pyocyanin. Of concern in many hospitals is the ease with which P. aeruginosa grows in flower vases, mop water, and even dilute disinfectants. The relative resistance to antibiotics that characterizes pseudomonads is still a problem

babesiosis

babesiosis, a tickborne disease Rodents are the reservoir in the wild; the tick vectors are most commonly Ixodes species bovine babesiosis, or tick fever. The human disease in the United States is caused by a protozoan, usually Babesia microti resembles malaria; the parasites replicate in the RBCs and cause a prolonged illness of fever, chills, and night sweats can be much more serious, sometimes fatal, in immunocompromised patients For example, the first human cases were observed in persons who had undergone splenectomy (removal of the spleen) Simultaneous treatment with the drugs atovaquone and azithromycin has been effective.

melioidosis

bacterial pathogen, Burkholderia pseudomallei, is a gram-negative rod formerly placed in the genus Pseudomonas closely resembled the bacterium causing glanders, a disease of horses major infectious disease in tropical regions of the world where the pathogen is widely distributed in moist soils melioidosis is most commonly seen as pneumonia. Mortality arises from dissemination, manifesting itself as septic shock can also appear as abscesses in various body tissues that resemble necrotizing fasciitis, as severe sepsis, and even as encephalitis Transmission is primarily by inhalation, but alternative infective routes are by inoculation through puncture wounds and ingestion Incubation periods can be very long, and occasional delayed-onset cases still surface in this population. Diagnosis is usually made by isolating the pathogen from body fluids. Serological tests in endemic areas are problematic because of widespread exposure to a similar, nonpathogenic bacterium. A rapid PCR test is used by public health laboratories Treatment by antibiotic is uncertain in effectiveness; the most commonly used is ceftazidime, a β-lactam antibiotic, months of treatment may be required

Pertussis (whooping cough)

bacterium Bordetella pertussis results in pertussis, or whooping cough. B. pertussis is a small, obligately aerobic, gram-negative coccobacillus possess a capsule, attach specifically to ciliated cells in the trachea, first impeding their ciliary action and then progressively destroying the cells; prevents the ciliary escalator system from moving mucus. B. pertussis produces several toxins Tracheal cytotoxin, a fixed cell wall fraction of the bacterium, is responsible for damage to the ciliated cells, and pertussis toxin enters the bloodstream and is associated with systemic symptoms of the disease Primarily a childhood disease, pertussis can be quite severe initial stage, called the catarrhal stage, resembles a common cold Prolonged sieges of coughing characterize the paroxysmal stage, or second stage When ciliary action is compromised, mucus accumulates, and the infected person desperately attempts to cough up these mucus accumulations. violence of the coughing in small children can actually result in broken ribs Gasping for air between coughs causes a whooping sound, hence the informal name of the disease. Coughing episodes occur several times a day for 1 to 6 weeks The convalescence stage, the third stage, may last for months Bc infants are less capable of coping with the effort of coughing to maintain an airway, irreversible damage to the brain occasionally occurs Diagnosis of pertussis is primarily based on clinical signs and symptoms pathogen can be cultured from a throat swab inserted through the nose on a thin wire and held in the throat while the patient coughs Culture of the fastidious pathogen requires care. As alternatives to culture, PCR methods can also be used to test the swabs for presence of the pathogen, a procedure that is required to diagnose the disease in infants Treatment of pertussis with antibiotics, most commonly erythromycin or other macrolides, is not effective after onset of the paroxysmal coughing stage but may reduce transmission.

Scalded skin syndrome

characteristic of the late stages of toxic shock syndrome (TSS) fever, vomiting, and a sunburnlike rash are followed by shock and sometimes organ failure, especially of the kidneys originally became known as a result of staphylococcal growth associated with the use of a new type of highly absorbent vaginal tampon; the correlation is especially high for cases in which the tampons remain in place too long. A novel staphylococcal toxin called toxic shock syndrome toxin 1 (TSST-1) is formed at the growth site and circulates in the bloodstream symptoms result of the superantigenic properties of the toxin

Acne

classified by type of lesion into three categories: comedonal acne, inflammatory acne, and nodular cystic acne. They require different treatments. Normally, skin cells that are shed inside the hair follicle are able to leave, but acne develops when cells are shed in higher than normal numbers, combine with sebum, and the mixture clogs the follicle. As sebum accumulates, whiteheads (comedos) form; if the blockage protrudes through the skin, a blackhead (comedone) forms. The dark color of blackheads is due not to dirt, but to lipid oxidation and other causes. Topical agents do not affect sebum formation, which is a root cause of acne and depends on hormones such as estrogens or androgens. Diet has no known effect on sebum production, but pregnancy, some hormone-based contraceptive methods, and hormonal changes with age do affect sebum formation and influence acne. Comedonal (mild) acne is usually treated with topical agents such as azelaic acid, salicyclic acid preparations, or retinoids (which are derivatives of vitamin A, such as tretinoin, tazarotene, or adapalene). These topical agents do not affect sebum formation. Inflammatory (moderate) acne arises from bacterial action, especially Cutibacterium acnes, an anaerobic diphtheroid commonly found on the skin. P. acnes has a nutritional requirement for glycerol in sebum; in metabolizing the sebum, it forms free fatty acids that cause an inflammatory response. Neutrophils that secrete enzymes that damage the wall of the hair follicle are attracted to the site. The resulting inflammation leads to the appearance of pustules and papules. At this stage, therapy is usually focused on preventing formation of sebum; topical agents are not effective for this. Inflammatory acne can also be treated by targeting P. acnes with antibiotics. The familiar nonprescription acne treatments containing benzoyl peroxide are effective against some bacteria, especially P. acnes, and also cause drying that helps loosen plugged follicles. Benzoyl peroxide is also available as a gel and in products where it is combined with antibiotics such as clindamycin and erythromycin. Nodular cystic acne is characterized by nodules or cysts, which are inflamed lesions filled with pus deep within the skin, prominent scars on the face and upper body, which often leave psychological scars as well. treatment for cystic acne is isotretinoin, which reduces the formation of sebum. Under the trade name of Accutane®, its distribution in the United States has been discontinued by the manufacturer. It is, however, distributed outside this country under the name Roaccutane®. Anyone considering the use of the drug should be warned that it is highly teratogenic, meaning it can cause serious damage to the developing fetus

tetanus

clostridium tetani, is an obligately anaerobic, endospore-forming, gram-positive rod. common in soil contaminated with animal fecal wastes The symptoms of tetanus are caused by an extremely potent neurotoxin, tetanospasmin, that is released upon death and lysis of the growing bacteria, enters the CNS via the peripheral nerves or the blood The bacteria themselves don't spread from the infection site, and there is no inflammation. In a muscle's normal operation, a nerve impulse initiates contraction of the muscle. At the same time, an opposing muscle receives a signal to relax so as not to oppose the contraction tetanus neurotoxin blocks the relaxation pathway so that both opposing sets of muscles contract, resulting in the characteristic muscle spasms The muscles of the jaw are affected early in the disease, preventing the mouth from opening, a condition known as lockjaw In extreme cases, spasms of the back muscles cause the head and heels to bow backward, a condition called opisthotonos Death results from spasms of the respiratory muscles. Because the microbe is an obligate anaerobe, the wound by which it enters the body must provide anaerobic growth conditions—for example, improperly cleaned deep wounds such as those caused by rusty (and therefore presumably dirtcontaminated) nails Effective vaccines for tetanus have been available since the 1940s. But vaccination was not always as common as it is today, where it is part of the standard DTaP (diphtheria, tetanus, and acellular pertussis) childhood vaccine Currently, about 94% of 6-year-olds in the United States have good immunity. The tetanus vaccine is a toxoid, an inactivated toxin that stimulates the formation of antibodies that neutralize the toxin produced by the bacteria A booster is required every 10 years to maintain good immunity, but many people do not obtain these vaccinations. Serological surveys show that at least 40% of the U.S. adult population does not have adequate protection Deaths are more likely to occur in persons age 60 years and older and in persons who are diabetic. rare disease—typically, fewer than 10 cases a year. Worldwide, an estimated 1 million cases occur annually, at least half in newborns. In many parts of the world, the severed umbilical cords of infants are dressed with materials such as soil, clay, and even cow dung mortality rate from tetanus is about 50% in developing areas; in the United States, it is about 25%. When TIG and toxoid are both injected, different sites must be used to prevent the TIG from neutralizing the toxoid

gangrene

death of tissue associated with loss of blood supply Substances released from dying and dead cells provide nutrients for many bacteria. Various species of the genus Clostridium, which are gram-positive, endospore-forming anaerobes widely found in soil and in the intestinal tracts of humans and domesticated animals, grow readily in such conditions. C. perfringens is the species most commonly involved in gangrene, but other clostridia and several other bacteria can also grow in such wounds. Once ischemia and the subsequent necrosis caused by impaired blood supply have developed, gas gangrene can develop, especially in muscle tissue As the C. perfringens microorganisms grow, they ferment carbohydrates in the tissue and produce gases (carbon dioxide and hydrogen) that swell the tissue. The bacteria produce toxins that move along muscle bundles, killing cells and producing necrotic tissue that is favorable for further bacterial growth. Eventually, these toxins and bacteria enter the bloodstream and cause systemic illness. Enzymes produced by the bacteria degrade collagen and proteinaceous tissue, facilitating the spread of the disease. Without treatment, the condition is fatal. Gas gangrene can also result from improperly performed abortions. C. perfringens, which resides in the genital tract of about 5% of all women, can infect the uterine wall and lead to gas gangrene, resulting in a life-threatening bloodstream infection surgical removal of necrotic tissue and amputation are the most common medical treatments for gas gangrene. When gas gangrene occurs in such regions as the abdominal cavity or the reproductive tract, the patient can be treated in a hyperbaric chamber, which contains a pressurized oxygenrich atmosphere. The oxygen saturates the infected tissues and thereby prevents the growth of the obligately anaerobic clostridia. Small chambers are available that can accommodate a gangrenous limb. The prompt cleaning of serious wounds and precautionary treatment with penicillin are the most effective steps in preventing gas gangrene

Burkitt's lymphoma

eastern Africa, frequent occurrence in children of a fast-growing tumor of the jaw most common childhood cancer in Africa. Burkitt suspected a viral cause of the tumor and a mosquito vector A virus was cultured from this material, and the electron microscope showed a herpeslike virus in the culture cells; it was named the Epstein-Barr virus (EB virus). The official name of this virus is human herpesvirus 4 (HHV-4). EB virus is clearly associated with Burkitt's lymphoma, but the mechanism by which it causes the tumor isn't understood. mosquitoborne malarial infections apparently foster the development of Burkitt's lymphoma by impairing the immune response to EB virus, which is almost universally present in human adults worldwide The virus has, in fact, become so adapted to humans that it is one of our most effective parasites. It establishes a lifelong infection in most people that is harmless and rarely causes disease In the United States, early treatment with anticancer drugs has a high success rate.

Buruli Ulcer

found primarily in western and central Africa. caused by Mycobacterium ulcerans, which is similar to the mycobacteria that cause tuberculosis and leprosy introduced into the skin, it causes a disease that progresses slowly with few serious early signs or symptoms. Eventually the result is a deep ulcer that often becomes massive and seriously damaging. Untreated, this can be so extensive as to require amputation or plastic surgery. This tissue damage is attributed to the production of a toxin, mycolactone. the infection is associated with contact with swamps and slow-flowing waters. The pathogen probably enters through a break in the skin from a minor cut or insect bite Buruli ulcer is diagnosed primarily by the appearance of the ulcer, although awareness is higher in endemic areas, and is treated by antimycobacterial drugs such as streptomycinrifampicin combinations.

lepromatous (progressive) form of leprosy

lepromatous (progressive) form of leprosy (which is much the same as multibacillary in the WHO system), skin cells are infected, and disfiguring nodules form all over the body Patients with this type of leprosy have had the least effective cell-mediated immune response, and the disease has progressed from the tuberculoid stage. Mucous membranes of the nose tend to become affected, and a lion-faced appearance is associated with this type of leprosy Deformation of the hand into a clawed form and considerable necrosis of tissue can also occur progression of the disease is unpredictable, and remissions may alternate with rapid deterioration The exact means of transfer of the leprosy bacillus is uncertain, but patients with lepromatous leprosy shed large numbers in their nasal secretions and in exudates (oozing matter) of their lesions. Most people probably acquire the infection when secretions containing the pathogen contact their nasal mucosa. However, leprosy is not very contagious and usually is transmitted only between people in fairly intimate and prolonged contact. The time from infection to the appearance of symptoms is usually measured in years, although children can have a much shorter incubation period. Death usually results not from the leprosy itself, but from complications, such as tuberculosis. Much of the public's fear of leprosy can probably be attributed to biblical and historical references to the disease. In the Middle Ages, people with leprosy were rigidly excluded from normal European society and sometimes even wore bells so that people could avoid them. This isolation might have contributed to the near disappearance of the disease in Europe. But patients with leprosy are no longer kept in isolation, because they can be made noncontagious within a few days by the administration of sulfone drugs. Most patients today are treated on an outpatient basis.

Cutaneous Mycoses

fungal disease Fungi that colonize the hair, nails, and the outer layer (stratum corneum) of the epidermis are called dermatophytes; they grow on the keratin present in those locations dermatomycoses, these fungal infections are more informally known as tineas or ringworm Tinea capitis, or ringworm of the scalp, is fairly common among elementary school children and can result in bald patches Three genera of fungi are involved in cutaneous mycosis. Trichophyton can infect hair, skin, or nails; Microsporum usually involves only the hair or skin; Epidermophyton affects only the skin and nails The topical drugs available without prescription for tinea infections include miconazole and clotrimazole. Athlete's foot is often difficult to cure. Topical allylamine preparations containing terbinafine or naftifine, as well as another allylamine, butenavine, are recommended and are now available without a prescription Extended application is usually required. When hair is involved infection is usually transmitted by contact with fomites Dogs and cats are also frequently infected with fungi that cause ringworm in children. Ringworm of the groin, or jock itch, is known as tinea cruris, and ringworm of the feet, or athlete's foot, is known as tinea pedis The moisture in such areas favors fungal infections. Ringworm of the fingernails or toenails is called tinea unguium, or onychomycosis effective. An oral antibiotic, griseofulvin, is often useful in such infections because it can localize in keratinized tissue, such as skin, hair, or nails. When nails are infected, oral itraconazole and terbinafine are the drugs of choice, but treatment may require weeks, and both must be used with caution because of potential severe side effects.

Ergot and Aflatoxin Poisoning

fungal infection Mycotoxins produced by Claviceps purpurea a fungus causing smut infections on grain crops, cause ergot poisoning when rye or other cereal grains contaminated with the fungus are ingested. The toxin can restrict blood flow in the limbs, with resulting gangrene may also cause hallucinogenic symptoms, producing bizarre behavior similar to that caused by LSD. Aflatoxin is a mycotoxin produced by the fungus Aspergillus flavus, a common mold. It has been found in many foods but is particularly likely to be found on peanuts Aflatoxin poisoning can cause serious damage to livestock when their feed is contaminated with A. flavus Although risk to humans is unknown, there is strong evidence aflatoxin contributes to cirrhosis of the liver and cancer of the liver in parts of the world, such as India and Africa, where food is subject to aflatoxin contamination

Streptococcal Skin Infections

gram-positive spherical bacteria, grow in chains cause a wide range of disease conditions beyond those covered in this chapter, including meningitis, pneumonia, sore throat, otitis media, endocarditis, puerperal fever, and even dental caries. As streptococci grow, secrete toxins and enzymes, virulence factors that vary with the different species. Among these toxins are hemolysins, which lyse red blood cells. Depending on the hemolysin they produce, streptococci are categorized as alpha-hemolytic, beta-hemolytic, and gamma-hemolytic (actually nonhemolytic) streptococci Hemolysins can lyse not only red blood cells, but almost any type of cell Beta-hemolytic streptococci are often associated with human disease. This group is further differentiated into serological groups, designated A through T, according to antigenic carbohydrates in their cell walls group A streptococci (GAS), which are synonymous with the species Streptococcus pyogenes, are the most important of the beta-hemolytic streptococci. most common human pathogens and are responsible for a number of human diseases—some of them deadly. produce certain enzymes, called streptolysins, that lyse red blood cells and are toxic to neutrophils. This group of pathogens is divided into over 80 immunological types according to the antigenic properties of the M protein found in some strains This protein is external to the cell wall on a fuzzy layer of fimbriae. The M protein prevents the activation of complement and allows the microbe to evade phagocytosis and killing by neutrophils and helps the bacteria adhere to and colonize mucous membranes. their capsule of hyaluronic acid. Exceptionally virulent strains have a mucoid appearance on blood-agar plates from heavy encapsulation and are rich in M protein. Hyaluronic acid is poorly immunogenic (it resembles human connective tissue), and few antibodies against the capsule are produced. The GAS produce substances that promote the rapid spread of infection through tissue and by liquefying pus. Among these are streptokinases (enzymes that dissolve blood clots), hyaluronidase (an enzyme that dissolves the hyaluronic acid in the connective tissue, where it serves to cement the cells together), and deoxyribonucleases (enzymes that degrade DNA). Streptococcal skin infections are generally localized, but if the bacteria reach deeper tissue, they can be highly destructive

tuberculosis (TB)

in recent decades co-infection with HIV has been a prominent cause of increasing susceptibility to infection and also of rapid progression from infection to active disease caused by the bacterium Mycobacterium tuberculosis, a slender rod and an obligate aerobe. The rods grow slowly (20-hour or longer generation time), sometimes form filaments, and tend to grow in clumps On the surface of liquid media, their growth appears moldlike, which suggested the genus name Mycobacterium Another mycobacterial species, Mycobacterium bovis is a pathogen mainly of cattle. M. bovis is the cause of bovine tuberculosis, which is transmitted to humans via contaminated milk or food. Bovine tuberculosis accounts for fewer than 1% of TB cases in the United States. M. bovis infections cause TB that primarily affects the bones or lymphatic system Other mycobacterial diseases also affect people in the late stages of HIV infection. A majority of the isolates are of a related group of organisms known as the M. avium-intracellulare complex. In the general population, infections by these pathogens are uncommon Mycobacteria stained with carbolfuchsin dye cannot be decolorized with acid-alcohol and are therefore classified as acid-fast These lipids might also be responsible for the resistance of mycobacteria to environmental stresses, such as drying. In fact, these bacteria can survive for weeks in dried sputum and are very resistant to chemical antimicrobials used as antiseptics and disinfectants A host is not usually aware of tuberculosis pathogens that invade the body and are defeated, which occurs 90% of the time. If immune defenses fail, however, the host becomes very much aware of the resulting disease A tragic demonstration of individual variation in resistance was the Lübeck disaster in Germany in 1926. By error, 249 babies were inoculated with virulent tuberculosis bacteria instead of the attenuated vaccine strain. Even though all received the same inoculum, there were only 76 deaths, and the remainder did not become seriously ill. Tuberculosis is most commonly acquired by inhaling the bacillus. Only very fine particles containing one to three bacilli reach the lungs, where they are usually phagocytized by a macrophage in the alveoli macrophages of a healthy individual become activated by the presence of the bacilli and usually destroy them About three-fourths of TB cases affect the lungs, but other organs can also become infected

meningoencephalitis

inflammation of the meninges and brain

Scabies

involves intense local itching and is caused by the tiny mite Sarcoptes scabiei burrowing under the skin to lay its eggs The burrows are often visible as slightly elevated, serpentine lines about 1 mm in width However, scabies may appear as a variety of inflammatory skin lesions, many of them secondary infections from scratching. mite is transmitted by intimate contact, including sexual contact, and is most often seen in family members, nursing home residents, and teenagers infected by children for whom they baby-sit The mite lives about 25 days, but by that time eggs have hatched and produced a dozen or so progeny. Scabies is usually diagnosed by microscopic examination of skin scrapings and usually is treated by topical application of permethrin. Difficult cases are sometimes treated with oral ivermectin

Ophthalmia Neonatorum

is a serious form of conjunctivitis caused by Neisseria gonorrhoeae, the cause of gonorrhea Large amounts of pus are formed; if treatment is delayed, ulceration of the cornea will usually result. The disease is acquired as the infant passes through the birth canal, and infection carries a high risk of blindness previously accounted for nearly one-quarter of all cases of blindness in the United States. antibiotics because of frequent coinfections by gonococci and sexually transmitted chlamydias, where the cost of antibiotics is prohibitive, a dilute solution of povidoneiodine has proven effective.

Conjunctivitis

is an inflammation of the conjunctiva, often called by the common name red eye, or pinkeye Haemophilus influenzae is the most common bacterial cause; viral conjunctivitis is usually caused by adenoviruses However, a broad group of bacterial and viral pathogens as well as allergies can also cause this condition popularity of contact lenses has been accompanied by an increased incidence of infections of the eye. This is especially true of the soft-lens varieties, which are often worn for extended periods Among the bacterial pathogens that cause conjunctivitis are pseudomonads, which can cause serious eye damage to prevent infection, contact lens wearers should not use homemade saline solutions, which are a frequent source of infection, and should scrupulously follow the manufacturer's recommendations for cleaning and disinfecting the lenses The most effective methods for disinfecting contact lenses involve applying heat; lenses that cannot be heated can be disinfected with hydrogen peroxide, which is then neutralized

Respiratory syncytial virus (RSV)

is probably the most common cause of viral respiratory disease in infants. It can also cause a life-threatening pneumonia in older adults, where it is easily misdiagnosed as influenza Virtually all children become infected by age 2—of whom about 1% require hospitalization. We have previously mentioned that RSV is sometimes implicated in cases of otitis media characteristic of causing cell fusion when grown in cell culture symptoms are coughing and wheezing that last for more than a week. Fever occurs only when there are bacterial complications Several rapid serological tests are now available that use samples of respiratory secretions to detect both the virus and its antibodies Naturally acquired immunity is very poor. The humanized monoclonal antibody, palivizumab, is recommended for prophylaxis in immunocompromised and other high-risk patients A recombinant vaccine for pregnant women to provide passive immunity for the infant is in clinical trials.

Pediculosis (Lice)

lice, called pediculosis head lice are easily transferred by head-to-head contact, such as occurs among children who know each other well The head louse, Pediculus humanus capitis, is not the same as the body; adapted to different areas of the body Only the body louse spreads diseases, such as epidemic typhus. Lice require blood from the host and feed several times a day. The victim is often unaware of these silent passengers until itching, which is a result of sensitization to louse saliva, develops several weeks later Scratching can result in secondary bacterial infections The head louse has legs especially adapted to grasp scalp hairs eggs are attached to hair shafts close to the scalp to benefit from a warmer incubation temperature, and they hatch in about a week very young stages of the louse are also called nits. Empty egg cases are whitish and more visible. They do not necessarily indicate the presence of live lice. As the hair grows (at the rate of about 1 cm a month), the attached nit moves away from the scalp lice have become adapted to the cylindrical hair shafts found on whites. In Africa, lice have adapted to the noncylindrical hair shafts, Pediculus humanus corporis many treatments for a condition, it is probably because none of them are really good. Nonprescription medications such as permethrin insecticide and pyrethrin insecticide are usually the first-choice treatment, but resistance has become common. Other topical preparations containing insecticides such as malathion and the more toxic lindane are also available (lindane is banned in some areas). A single-dose treatment with orally administered ivermectin is occasionally used. A silicone-based product, LiceMD®, is effective and nontoxic. The active principle, dimethicone, blocks the breathing tubes of the louse. Combing out the nits with fine-toothed louse combs is another treatment option. This is a difficult, time-consuming procedure that has actually led to the appearance of professional removal services in some cities: expensive, but often worth the price to busy parents.

Roseola

mild, very common childhood disease a high fever for a few days, which is followed by a rash over much of the body lasting for a day or two. Recovery leads to immunity. The pathogens are human herpesviruses 6 (HHV-6) and 7 (HHV-7)—the latter is responsible for 5-10% of roseola cases. Both viruses are present in the saliva of most adults.

Subcutaneous Mycoses

more serious than cutaneous mycoses. Even when the skin is broken, cutaneous fungi do not seem to be able to penetrate past the stratum corneum, bc they cannot obtain sufficient iron for growth in the epidermis and the dermis Usually subcutaneous mycoses are caused by fungi that inhabit the soil, especially decaying vegetation, and penetrate the skin through a small wound that allows entry the most common disease of this type is sporotrichosis, caused by the dimorphic fungus Sporothrix schenkii. Most cases occur among gardeners or other people working with soil forms a small ulcer on the hands. The fungus often enters the lymphatic system in the area and there forms similar lesions is seldom fatal and is effectively treated with itraconazole, or by ingesting a dilute solution of potassium iodide.

Diaeehea

mortality from childhood diarrhea could be halved by oral rehydration therapy (replacement of lost fluids and electrolytes). usually a solution of sodium chloride, potassium chloride, glucose, and sodium bicarbonate to replace lost fluids and electrolytes. recommendation to replenish losses of zinc during diarrheal episodes with a course of zinc tablets. This has been found to reduce the duration and severity of diarrheal episodes and even help prevent future episodes for 2 or 3 months

Epidemiology of Influenza

mortality rate from the disease is usually not high, less than 1%, and these deaths are mainly among the very young and the very old Mutations of the influenza virus are more likely to occur in humans, who have a long life span virus must continue to mutate in order to evade accumulating immunological resistance. Swine and poultry, in contrast, have short life spans and the viruses infecting them are less likely to accumulate mutations. An H1N1 influenza virus, which has little pressure to mutate in farm-reared swine, tends to remain little changed in successive generations of the animal.

Traveler's Diarrhea

most common bacterial cause is ETEC; the second most frequent isolate is EAEC. Traveler's diarrhea can also be caused by other gastrointestinal pathogens, such as Salmonella, Shigella, and Campylobacter most cases the causative agent is never identified, and chemotherapy is not attempted. Once contracted, the best treatment is the usual oral rehydration recommended for all diarrhea In severe cases, antimicrobial drugs may be necessary. Prescribed antibiotics may provide some protection; another option is to take an over-the-counter drug such as Lomotil® to treat the symptoms, but the best advice in risky areas is to prevent infection.

Diagnosis of Malaria

most common diagnostic test is the blood smear, which requires a microscope time-consuming and requires skill in interpretation. It is still the "gold standard" for diagnosis when a well-trained staff is available Rapid, antigene detecting diagnostic tests that can be performed by staff with minimal training have been developed but are relatively expensive High-quality rapid diagnostic tests that are affordable and perform reliably under field conditions are urgently needed It has been found that only about half of such patients given prescriptions for antimalarial drugs actually had the disease.

Viral meningitis

much more common than bacterial meningitis but tends to be a mild disease meningitis caused by a virus and not as severe as pyrogenic meningitis caused by a varied group of viruses termed enteroviruses, w/ grow well in the throat and intestinal tract

Pathogenesis of Tuberculosis

mycolic acids of the cell wall strongly stimulate an inflammatory response in the host. Coughing, the more obvious symptom of the lung infection, also spreads the infection by bacterial aerosols Sputum may become bloodstained as tissues are damaged, and eventually blood vessels may become so eroded that they rupture, resulting in fatal hemorrhaging The disseminated infection is called miliary tuberculosis The body's remaining defenses are overwhelmed, and the patient suffers weight loss and a general loss of vigor

Influenza Vaccines

not been possible to make a vaccine for influenza that gives long-term immunity to the general population Although it isn't difficult to make a vaccine for a particular antigenic strain of virus, each new strain of circulating virus must be identified in time, usually about February, for the useful development and distribution of a new vaccine later that year Strains of the influenza virus are collected in about 100 centers worldwide, then analyzed in central laboratories. This information is then used to decide on the composition of the vaccines to be offered for the next flu season The vaccines are usually multivalent—directed at the three or four most important strains in circulation at the time. A major problem is that production methods for vaccines require growing the virus in egg embryos, times of 6 to 9 months A recombinant influenza vaccine has been produced from HA protein expressed by a baculovirus (an insect pathogen) and grown in insect cells. Cell-based vaccines can be produced faster because the cells can be kept frozen.

bullous impetigo

other type of impetigo caused by a staphylococcal toxin and is a localized form of staphylococcal scalded skin syndrom there are two exotoxins; exfoliative toxin A, w/ remains localized, causes bullous impetigo, and exfolioative toxin B, which circulates to distant sites, causes scalded skin syndrome Both toxins cause a separation of the skin layers, exfoliation. Outbreaks of bullous impetigo are a frequent problem in hospital nurseries, where the condition is known as pemphigus neonatorum, or impetigo of the newborn

Fifth Disease (Erythema Infectiosum)

produces no symptoms at all in about 20% of individuals infected by the virus (human parvovirus B19, first identified in 1989) Symptoms are similar to a mild case of influenza, but there is a distinctive "slapped-cheek" facial rash that slowly fades In adults who missed an immunizing infection in childhood, the disease may cause anemia, an episode of arthritis, or, rarely, miscarriage

Neonatal herpes

s usually results from transmission of the herpes simplex viruses (HSV-1or HSV-2) from the mother at delivery. It has a mortality rate of 60%, and survivors have central nervous system disorders such as seizures

peptic ulcer disease

spiral-shaped, microaerophilic bacterium observed in the biopsied tissue of stomach ulcer patients. Now named Helicobacter pylori, it is accepted that this microbe is responsible for most cases of peptic ulcer disease. This syndrome includes gastric and duodenal ulcers. (The duodenum is the first few centimeters of the small intestine.) About 30-50% of the population in the developed world become infected; the infection rate is higher elsewhere Only about 15% of people infected develop ulcers, so certain host factors are probably involved For example, people with type O blood are more susceptible, which is also true of cholera H. pylori is also designated as a carcinogenic bacterium. Gastric cancer develops in about 3% of people infected with these bacteria The stomach mucosa contains cells that secrete gastric juice containing proteolytic enzymes and hydrochloric acid that activates these enzymes. Other specialized cells produce a layer of mucus that protects the stomach itself from digestion If this defense is disrupted, an inflammation of the stomach (gastritis) results. This inflammation can then progress to an ulcerated area H. pylori can grow in the highly acidic environment of the stomach, which is lethal for most microorganisms. H. pylori produces large amounts of an especially efficient urease, an enzyme that converts urea to the alkaline compound ammonia, resulting in a locally high pH in the area of growth eradication of H. pylori with antimicrobial drugs usually leads to the disappearance of peptic ulcers. Several antibiotics, usually administered in combination, have proven effective. Bismuth subsalicylate (Pepto-Bismol®) is also effective and is often part of the drug regimen When the bacteria are successfully eliminated, the recurrence rate of the ulcer is only about 2-4% a year. Reinfection can result from many environmental sources but is less likely in areas with high standards of sanitation; in fact, there is some evidence that infection by H. pylori is slowly disappearing in developed countries reliable diagnostic test requires a biopsy of tissue and culture of the organism. An interesting diagnostic approach is the urea breath test. The patient swallows radioactively labeled urea; if the test is positive, CO2 labeled with radioactivity can be detected in the breath within about 30 minutes. This test is most useful for determining the effectiveness of chemotherapy because a positive test is an indication of live H. pylori Diagnostic tests of stools to detect antigens (not antibodies) for H. pylori are suitable for follow-up tests following therapy

Psittacosis (Ornithosis)

term psittacosis is derived from association w/ psittacine birds, such as parakeets and other parrots. It was later found that the disease can also be contracted from many other birds, such as pigeons, chickens, ducks, and turkeys. Therefore, the more general term ornithosis has come into use. causative agent is Chlamydophila psittaci, a gram-negative, obligate intracellular bacterium generic terms chlamydial and chlamydiae One way chlamydiae differ from rickettsias, w/ are also obligate intracellular bacteria, is that chlamydiae form tiny elementary bodies as one part of their life cycle Unlike most rickettsias, elementary bodies are resistant to environmental stress; therefore, they can be transmitted through air and do not require a bite to transfer the infective agent directly from one host to another Psittacosis is a form of pneumonia that usually causes fever, coughing, headache, and chills Subclinical infections are very common, and stress appears to enhance susceptibility to the disease. Disorientation, or even delirium in some cases, indicates that the nervous system can be involved usually spread by contact with the droppings and other exudates of fowl. One of the most common modes of transmission is inhalation of dried particles from droppings birds themselves usually have diarrhea, ruffled feathers, respiratory illness, and a generally droopy appearance diagnosed by isolating the bacterium in embryonated eggs or by cell culture. PCR can be used to identify the Chlamydia species No vaccine is available, but tetracyclines are effective antibiotics in treating humans and animals Effective immunity does not result from recovery, even when high titers of antibody are present in the serum main danger is late diagnosis. Before antibiotic therapy was available, the mortality rate was about 15-20%. C. psittasci is listed by the CDC as a potential bioterrorism weapon

Spotted Fevers

tickborne typhus, or Rocky Mountain spotted fever, is probably the best-known rickettsial disease in the United States caused by Rickettsia rickettsii, most common in the southeastern states and Appalachia This rickettsia is a parasite of ticks and is usually passed from one generation of ticks to another through their eggs, a mechanism called transovarian passage in endemic areas, perhaps 1 out of every 1000 ticks is infected. In different parts of the United States, different ticks are involved— in the west, the wood tick Dermacentor andersoni; in the east, the dog tick Dermacentor variabilis About a week after the tick bites, a macular rash develops that is sometimes mistaken for measles however, it often appears on palms and soles, where viral rashes do not occur. The rash is accompanied by fever and headache Death, which occurs in about 3% of the approximately 4000 cases reported each year, is usually caused by kidney and heart failure. Serological tests don't become positive until late in the illness. Diagnosis before the typical rash appears is difficult because symptoms vary widely. Also, on dark-skinned individuals, the rash is difficult to see. A misdiagnosis can be costly; if treatment is not prompt and correct, the mortality rate is about 20%. Antibiotics such as tetracycline and chloramphenicol are very effective if administered early enough. No vaccine is available.

Yellow Fever

viral hemorrhagic disease Most hemorrhagic fevers are zoonotic diseases; they appear in humans only from infectious contact with their normal animal hosts. Some of them have been medically familiar for so long that they are considered "classic" hemorrhagic fevers First among these is yellow fever. The yellow fever virus is injected into the skin by a mosquito, A. aegypti In the early stages of severe cases of the disease, the person experiences fever, chills, and headache, followed by nausea and vomiting This stage is followed by jaundice, a yellowing of the skin that gave the disease its name. This coloration reflects liver damage, which results in the deposit of bile pigments in the skin and mucous membranes. The mortality rate for yellow fever is high, about 20%. Monkeys are a natural reservoir for the virus, but human-tomhuman transmission can maintain the disease Local control of mosquitoes and immunization of the exposed population are effective controls in urban areas Diagnosis is by clinical signs, but it can be confirmed by a rise in antibody titer or isolation of the virus from the blood There is no specific treatment for yellow fever The vaccine is an attenuated live viral strain and yields a very effective immunity

Acanthamoeba Keratitis

well over 4000 cases have been diagnosed in the United States ameba has been found in fresh water, tap water, hot tubs, and soil. Most recent cases have been associated with the wearing of contact lenses, although any cornea damaged by trauma or infection is susceptible Contributing factors are inadequate, unsanitary, or faulty disinfecting procedures (only heat will reliably kill the cysts), homemade saline solutions, and wearing the contact lenses overnight or while swimming. In its early stages, the infection consists of only a mild inflammation, but later stages are often accompanied by severe pain. If started early, treatment with 2% chlorhexidine and propamidine isethionate eye drops or topical neomycin has been successful Damage is often so severe as to require a corneal transplant or even removal of the eye. Diagnosis is confirmed by the presence of trophozoites and cysts in stained scrapings of the cornea

S. pyogenes

when infects the dermal layer of the skin causes a serious disease, erysipelas the skin erupts into reddish patches with raised margins, It can progress to local tissue destruction and even enter the bloodstream, causing sepsis ( usually appears first on the face and often has been preceded by a streptococcal sore throat High fever is common. Fortunately, S. pyogenes has remained sensitive to β-lactam-type antibiotics, especially cephalosporin