Micro Exam 4

syphilis

A sexually transmitted bacterial disease caused by the spirochete Treponema pallidum. Brought into direct contact with mucous membranes or abraded skin, T. pallidum binds avidly by its hooked tip to the epithelium PRIMARY - The earliest indication is the appearance of a hard chancre at the site of entry of the pathogen. A chancre appears after an incubation period that varies from 9 days to 3 months. The chancre begins as a small, red, hard bump that enlarges and breaks down, leaving a shallow crater with firm margins. SECONDARY - About 3 weeks to 6 months after the chancre heals, the secondary stage appears. By then, many systems of the body have been invaded, and the signs and symptoms are more profuse and intense. Initial symptoms are fever, headache, and sore throat, followed by lymphadenopathy and a peculiar red or brown rash that breaks out on all skin surfaces, including the palms of the hands and the soles of the feet. A person's hair often falls out. LATENCY & TERTIARY - about 30% of infections enter a highly varied latent period that can last for 20 years or longer. During latency, although antibodies to the bacterium are readily detected, the bacterium itself is not. The final stage of the disease (tertiary) is relatively rare today because of widespread use of antibiotics. Cardiovascular syphilis results from damage to the small arteries in the aortic wall. As the fibers in the wall weaken, the aorta is subject to distension and fatal rupture. In one form of tertiary syphilis, painful, swollen tumors called gummas develop in tissues such as the liver, skin, bone, and cartilage CONGENITAL - The bacterium can pass from a pregnant woman's circulation into the placenta and can be carried throughout the fetal tissues. Infants often demonstrate such signs as profuse nasal discharge, skin eruptions, bone deformation, and nervous system abnormalities. The late form gives rise to an unusual assortment of problems in the bones, eyes, inner ear, and joints and causes the malformation of teeth. The number of congenital syphilis cases is closely tied to the incidence in adults.

healthcare associated pneumonia

type of pneumonia most commonly associated with mechanical ventilation, via an endotracheal or tracheostomy tube caused by MRSA strains of Staphylococcus aureus, as well as nonresistant strains Elevating patients' heads to a 45-degree angle helps reduce aspiration of secretions. Good preoperative education of patients about the importance of deep breathing and frequent coughing can reduce postoperative infection rates.

antigenic drift

Minor antigenic changes in the influenza A virus due to mutations in the spikes' genes.

whooping cough (pertussis)

After an incubation period of from 3 to 21 days, the *catarrhal stage* begins when bacteria present in the respiratory tract cause what appear to be cold symptoms, most notably a runny nose. This stage lasts 1 to 2 weeks. The disease worsens in the second (*paroxysmal*) stage, which is characterized by severe and uncontrollable coughing (a paroxysm is a convulsive attack). The common name for the disease comes from the sound a patient makes as he tries to grab a breath between uncontrollable bouts of coughing. The violent coughing spasms can result in burst blood vessels in the eyes or even vomiting. In the worst cases, seizures result from small hemorrhages in the brain. As in any disease, the *convalescent period* is the time when numbers of bacteria are decreasing and no longer cause ongoing symptoms. But the active stages of the disease damage the cilia on respiratory tract epithelial cells, and complete recovery of these surfaces requires weeks or even months. During this time, other microorganisms can more easily colonize and cause secondary infection. Bordetella pertussis is a very small, gram-negative rod. Sometimes it looks like a coccobacillus. It is strictly aerobic and fastidious, having specific nutritional requirements for successful culture. It is absolutely essential for the bacterium to attach firmly to the epithelial cells of the mouth and throat, and it does so using specific adhesive molecular structures on its surface. One of these structures is called filamentous hemagglutinin (FHA). It is a fibrous structure that surrounds the bacterium like a capsule and is secreted in soluble form. In that form, it can act as a bridge between the bacterium and the epithelial cell. The two most important exotoxins are pertussis toxin and tracheal cytotoxin. Pertussis toxin triggers excessive amounts of cyclic AMP to accumulate in affected cells. This results in copious production of mucus and a variety of other effects in the respiratory tract and the immune system. Tracheal cytotoxin results in more direct destruction of ciliated cells. The cells are no longer capable of clearing mucus and secretions, leading to the extraordinary coughing required to get relief. Another important contributor to the pathology of the disease is B. pertussis endotoxin. As always with endotoxins, its release leads to the production of a host of cytokines that have direct and indirect effects on physiological processes and on the host response.

Babesiosis

Babesia is a protozoan organism that infects red blood cells. It produces symptoms similar to those of to Ehrlichia and Anaplasma. It is also carried by ticks. It is often diagnosed via a blood smear; the protozoan is visible inside red blood cells

sepsis

Bacteria cause the vast majority of septicemias and are evenly divided between gram-positive and gram-negative organisms. Gram-negative bacteria multiplying in the blood release large amounts of endotoxin into the bloodstream, stimulating a massive inflammatory response mediated by a host of cytokines. This response invariably leads to a drastic drop in blood pressure, a condition called endotoxic shock. Gram-positive bacteria can instigate a similar cascade of events when fragments of their cell walls are released into the blood. Fever is a prominent feature. The patient appears very ill and may have an altered mental state, shaking chills, and gastrointestinal symptoms. Often an increased breathing rate is exhibited, accompanied by respiratory alkalosis. Low blood pressure is a hallmark of this condition and is caused by the inflammatory response to infectious agents in the bloodstream, which leads to a loss of fluid. This condition is the most dangerous feature of the disease, often culminating in death. can be traced to parenteral introduction of the microorganisms via intravenous lines or surgical procedures. Other infections may arise from serious urinary tract infections or from renal, prostatic, pancreatic, or gallbladder abscesses. Patients with underlying spleen malfunction may be predisposed to multiplication of microbes in the bloodstream.

hantavirus pulmonary syndrome

Common features of the prodromal phase of this infection include fever, chills, myalgias (muscle aches), headache, nausea, vomiting, and diarrhea or a combination of these symptoms. A cough is common but is not a prominent early feature. Initial symptoms resemble those of other common viral infections. Soon, a severe pulmonary edema occurs and causes acute respiratory distress (acute respiratory distress syndrome [ARDS] has many microbial and nonmicrobial causes; this is only one of them). The acute lung symptoms appear to be due to the presence of large amounts of this antigen, which becomes disseminated throughout the bloodstream (including the capillaries surrounding the alveoli of the lung). Massive amounts of fluid leave the blood vessels and flood the alveolar spaces in response to the inflammatory stimulus, causing severe breathing difficulties and a drop in blood pressure. The propensity to cause a massive inflammatory response could be considered a virulence factor for this organism. transmitted via airborne dust contaminated with the urine, feces, or saliva of infected rodents. Deer mice and other rodents can harbor one of the multiple strains identified throughout the world today, exhibiting few apparent symptoms

Q fever

Coxiella burnetii very small, pleomorphic, gram-negative bacterium. It is an intracellular parasite, and it produces an unusual type of endospore-like structure. Humans acquire infection largely by means of environmental contamination and airborne spread. Birth products such as placentas of infected domestic animals contain large numbers of bacteria. Other sources of infectious material include urine, feces, milk, and airborne particles from infected animals People at highest risk are farm workers, meat cutters, veterinarians, laboratory technicians, and consumers of raw milk products

Ehrlichiosis

Ehrlichia is a small, intracellular bacterium with a strict parasitic existence and association with ticks The signs and symptoms include an acute febrile state resulting in headache, muscle pain, and rigors. Most patients recover rapidly with no lasting effects, but about 5% of older, chronically ill patients can die. Rapid diagnosis is done through PCR tests and indirect fluorescent antibody tests

diphtheria

For hundreds of years, it was one of the most important causes of childhood death, but in the last 50 years, both the number of cases and the fatality rate have steadily declined throughout the world. caused by an exotoxin manufactured by Corynebacterium diphtheriae, a non-endospore-forming, gram-positive, club-shaped bacterium. The symptoms are experienced initially in the upper respiratory tract. At first the patient experiences a sore throat, lack of appetite, and low-grade fever. The most striking symptom of this disease is the characteristic membrane, usually referred to as a pseudomembrane, that forms on the tonsils or pharynx. The membrane is formed by the bacteria and consists of bacterial cells, fibrin, lymphocytes, and dead tissue cells and may be quite extensive. It adheres to tissues and cannot easily be removed. It may eventually completely block respiration. The patient may or may not recover after this crisis. Exotoxin manufactured by the bacterium may penetrate the bloodstream and travel throughout the body.

postinfectious encephalitis

Infection with measles and other childhood rash diseases can result 1 to 2 weeks later in an inappropriate immune response with consequences in the CNS. this infection is thought to be a result of immune system action and not of direct viral invasion of neural tissue. Very rarely, it can occur after immunization with vaccines comprised of live attenuated virus. Note that it is distinct from another possible sequela of measles virus infection called SSPE

antigenic shift

Major changes in the influenza A virus due to recombination of viral strains from two different host species.

tuberculosis

Mycobacterium tuberculosis, informally called the tubercle bacillus. It is a long and thin acid-fast rod. It is a strict aerobe and is not referred to as gram-positive or gram-negative because its acid-fast nature is much more relevant in a clinical setting. It grows very slowly, with a generation time of 15 to 20 hours. A period of up to 6 weeks is required for colonies to appear in culture. In general, humans are rather easily infected with the bacterium but are resistant to the disease. Estimates project that only about 5%-10% of infected people actually develop a clinical case of tuberculosis. The majority of TB cases are contained in the lungs, even though disseminated TB bacteria can give rise to tuberculosis in any organ of the body. Clinical tuberculosis is divided into primary tuberculosis, secondary (reactivation or reinfection) tuberculosis, and disseminated tuberculosis. transmitted almost exclusively by fine droplets of respiratory mucus suspended in the air. In the IGRA test, a patient's blood is drawn and incubated in test kits that detect the presence of T cells that react with M. tuberculosis antigens. If they have been so sensitized, they will release interferon-gamma (IFN-γ) after binding the antigens. High levels of IFN-γ trigger a positive response. The advantage of these tests is that no return visit is required. Recently, a PCR method has become available. Known as Xpert MTB/RIF, it simultaneously detects M. tuberculosis and determines its rifampin sensitivity within 100 minutes. The WHO started encouraging its use in 2010; by 2015, the majority of even many low-income countries had purchased the kits.

Gonorrhea

Neisseria gonorrhoeae, also known as the gonococcus In the male, infection of the urethra elicits urethritis, painful urination and a yellowish discharge, although a relatively large number of cases are asymptomatic. In most cases, infection is limited to the distal urogenital tract, but it can spread from the urethra to the prostate gland and epididymis In the female, it is likely that both the urinary and genital tracts will be infected during sexual intercourse. A mucopurulent (containing mucus and pus) or bloody vaginal discharge occurs in about half of the cases, along with painful urination if the urethra is affected. Major complications occur when the infection ascends to higher reproductive structures such as the uterus and fallopian tubes. One disease resulting from this progression is salpingitis (inflammation of the fallopian tubes); may be isolated, or it may also include inflammation of other parts of the upper reproductive tract (pelvic inflammatory disease (PID)). The buildup of scar tissue from PID can block the fallopian tubes, causing sterility or ectopic pregnancies Children born to gonococcus carriers are also in danger of being infected as they pass through the birth canal. Because of the potential harm to the fetus, physicians usually screen pregnant mothers for its presence. Gonococcal eye infections are very serious and often result in keratitis, ophthalmia neonatorum, and even blindness. A universal precaution to prevent such complications is the use of antibiotic eyedrops or ointments (usually erythromycin) for newborn babies.

Giardia lamblia

Observed straight on, the trophozoite has a unique symmetrical heart shape with organelles positioned in such a way that it resembles a face. Four pairs of flagella emerge from the ventral surface, which is concave and acts as a suction cup for attachment to a substrate. Giardia cysts are small and compact, and they contain four nuclei. Typical symptoms include diarrhea of long duration, abdominal pain, and flatulence. Stools have a greasy, malodorous quality. Fever is usually not present. Ingested cysts enter the duodenum, germinate, and travel to the jejunum to feed and multiply. Some trophozoites remain on the surface, while others invade the deeper crypts to varying degrees. Superficial invasion by trophozoites causes damage to the epithelial cells, edema, and infiltration by white blood cells, but these effects are reversible. The presence of the protozoan leads to malabsorption (especially of fat) in the digestive tract and can cause significant weight loss. The protozoan has been isolated from the intestines of beavers, cattle, coyotes, cats, and human carriers, but the precise reservoir is unclear. Cysts are usually ingested with water and food or swallowed after close contact with infected people or contaminated objects. Infection can occur with a dose of only 10 to 100 cysts Avoiding drinking from freshwater sources is the major preventive measure that can be taken. The agent is killed by boiling, ozone, and iodine; however, the amount of chlorine used in municipal water supplies does not destroy the cysts.

Urinary Schistosomiasis

One particular species of this trematode (helminth) lodges in the blood vessels of the bladder. the first symptoms of infestation are itchiness in the area where the helminth enters the body, followed by fever, chills, diarrhea, and cough. Urinary tract symptoms occur at a later date. Remember that adult flukes can live for many years and, by eluding the immune defenses, cause chronic infection. The urinary manifestations occur if a host is infected with Schistosoma haematobium. able to invade intact skin and attach to vascular endothelium manifestations occur when the eggs in the bladder induce a massive granulomatous response that leads to leakage in the blood vessels and blood in the urine. Significant portions of the bladder eventually can be filled with granulomatous tissue and scar tissue. Function of the bladder is decreased or halted altogether. Chronic infection with S. haematobium can also lead to bladder cancer.

Mycoplasma pneumoniae

Pneumonias caused by a handful of bacteria are often called atypical pneumonia—atypical in the sense that the symptoms do not resemble those of pneumococcal or other severe pneumonia. They are more like a bad case of the common cold, except that there is mucus accumulation in the lungs. Mycoplasmas are among the smallest known self-replicating microorganisms. They naturally lack a cell wall and are therefore irregularly shaped. They may resemble cocci, filaments, doughnuts, clubs, or helices. They are free-living but fastidious, requiring complex medium to grow in the lab. transmitted by aerosol droplets among people confined in close living quarters, especially families, students, and the military

West Nile Virus

The West Nile virus emerged in the United States in 1999, and by 2008 the CDC were reporting that 1% of people in the United States—or approximately 3 million people—had evidence of past or present infection. All encephalitis cases are treated with acyclovir, in case they are caused by this virus, against which acyclovir is effective. The arboviruses respond to no current treatment, but there is no harm done by treating with acyclovir before diagnosis is complete.

Trichuris trichiura

The common name for this nematode—whipworm—refers to its likeness to a miniature buggy whip. Humans are the sole host. Trichuriasis has its highest incidence in areas of the tropics and subtropics that have poor sanitation. Embryonic eggs deposited in the soil are not immediately infective and continue development for 3 to 6 weeks in this habitat. Ingested eggs hatch in the small intestine, where the larvae attach, penetrate the outer wall, and go through several molts. The mature adults move to the large intestine and gain a hold with their long, thin heads, while the thicker tail dangles free in the intestinal lumen. Following sexual maturation and fertilization, the females eventually lay 3,000 to 5,000 eggs daily into the bowel. The entire cycle requires about 90 days, and untreated infection can last up to 2 years. Symptoms of this infection may include localized hemorrhage of the bowel caused by worms burrowing and piercing intestinal mucosa. This can also provide a portal of entry for secondary bacterial infection. Heavier infections can cause dysentery, loss of muscle tone, and rectal prolapse, which can prove fatal in children.

histoplasma capsulatum

The most serious systemic forms of histoplasmosis occur in patients with defective cell-mediated immunity such as AIDS patients. In these cases, the infection can lead to lesions in the brain, intestines, heart, liver, spleen, bone marrow, and skin. Persistent colonization of patients with emphysema and bronchitis causes chronic pulmonary histoplasmosis, a complication that has signs and symptoms similar to those of tuberculosis. The organism is endemically distributed on all continents except Australia. Its highest rates of incidence occur in the eastern and central regions of the United States, especially in the Ohio Valley Usually, it appears as spherical, "fish-eye" yeasts intracellularly in macrophages and occasionally as free yeasts in samples of sputum and cerebrospinal fluid. A urine antigen test is also available.

lassa fever

The virus is spread to humans through aerosolization of rat droppings, urine, hair, and so forth. Eating food contaminated by rat excretions also transmits the virus. Infected persons can spread it to other people through their own secretions. Vertical transmission also occurs, and the disease leads to spontaneous abortions in 95% of infected pregnant women.

Jamestown Canyon Virus

This arbovirus is maintained in nature by cycling between mosquitoes and deer or moose. The virus is found throughout North America but until recently was rarely seen in humans. Before 2009, there were fewer than 3 human cases a year reported. In 2013, 22 cases were reported.

Leptospirosis

This infection is a zoonosis associated with wild animals and domesticated animals. It can affect the kidneys, liver, brain, and eyes caused by Leptospira interrogans There are nearly 200 different serotypes of this species distributed among various animal groups, which accounts for extreme variations in the disease manifestations in humans. During the early—leptospiremic—phase, the pathogen appears in the blood and cerebrospinal fluid. Symptoms are sudden high fever, chills, headache, muscle aches, conjunctivitis, and vomiting. During the second—immune—phase, the blood infection is cleared by natural defenses. This period is marked by milder fever; headache due to leptospiral meningitis; and Weil's syndrome, a cluster of symptoms characterized by kidney invasion, hepatic disease, jaundice, anemia, and neurological disturbances. Long-term disability and even death can result from damage to the kidneys and liver, but they occur primarily with the most virulent strains and in elderly persons. Leptospires that are shed in the urine of an infected animal can survive for several months in neutral or alkaline soil or water. Infection occurs almost entirely through contact of skin abrasions or mucous membranes with animal urine or some environmental source containing urine.

Fasciola hepatica

This liver fluke is a common parasite in sheep, cattle, goats, and other mammals and is occasionally transmitted to humans. Periodic outbreaks in temperate regions of Europe and South America are associated with eating wild watercress. The life cycle is very complex, involving the mammal as the definitive host, the release of eggs in the feces, the hatching of eggs in the water into miracidia, invasion of freshwater snails, development and release of cercariae, encystment of metacercariae on a water plant, and ingestion of the cyst by a mammalian host eating the plant. The cysts release young flukes into the intestine that wander to the liver, lodge in the gallbladder, and develop into adults. Humans develop symptoms of vomiting, diarrhea, hepatomegaly, and bile obstruction only if they are chronically infected by a large number of flukes

Enterobius vermicularis

This nematode is often called the pinworm, or seatworm. It is the most common worm disease of children in temperate zones. Freshly deposited eggs have a sticky coating that causes them to lodge beneath the fingernails and to adhere to fomites. Upon drying, the eggs become airborne and settle in house dust. Eggs are ingested from contaminated food or drink and from self-inoculation from one's own fingers. Eggs hatch in the small intestine and release larvae that migrate to the large intestine. There the larvae mature into adult worms and mate. The hallmark symptom of this condition is pronounced anal itching when the mature female emerges from the anus and lays eggs. Although infection is not fatal and most cases are asymptomatic, the afflicted child can suffer from disrupted sleep and sometimes nausea, abdominal discomfort, and diarrhea. A simple rapid test can be performed by pressing a piece of transparent adhesive tape against the anal skin and then applying it to a slide for microscopic examination. When one member of the family is diagnosed, the entire family should be tested and/or treated because it is likely that multiple members are infected.

Diphyllobothrium latum

This tapeworm has an intermediate host in fish. It is common in the Great Lakes, Alaska, and Canada. Humans are its definitive host. It develops in the intestine and can cause long-term symptoms. It can be transmitted in raw food such as sushi and sashimi made from salmon. (Reputable sushi restaurants employ authentic sushi chefs who are trained to carefully examine fish for larvae and other signs of infection.) It must also be recognized that transmission of this pathogen can occur in the United States through the consumption of undercooked or lightly smoked trout, perch, or pike—all very common fish to the American freshwater sport fisherman. As is the case with most tapeworms, symptoms are minor and usually vague and include possible abdominal discomfort or nausea. The tapeworm seems to have the ability to absorb and use vitamin B12, making it unavailable to its human host. Anemia is therefore sometimes reported with this infection. You should be aware that certain people of Scandinavian descent have a genetic predisposition for not adsorbing B12. In these patients, Diphyllobothrium latum infection can be quite dangerous.

hepatitis

When certain viruses infect the liver an inflammatory disease marked by necrosis of hepatocytes and a response by mononuclear white blood cells that swells and disrupts the liver architecture. This pathologic change interferes with the liver's excretion of bile pigments such as bilirubin into the intestine. When bilirubin, a greenish-yellow pigment, accumulates in the blood and tissues, it causes jaundice, a yellow tinge in the skin and eyes.

Schistosomiasis Liver Disease

When liver swelling or malfunction is accompanied by eosinophilia, this disease should be suspected. The disease is caused by the blood flukes Schistosoma mansoni and S. japonicum, species that are morphologically and geographically distinct but share similar life cycles, transmission methods, and general disease manifestations. one of the few infectious agents that can invade intact skin. The first symptoms of infection are itchiness in the area where the worm enters the body, followed by fever, chills, diarrhea, and cough. The most severe consequences, associated with chronic infection, are hepatomegaly, liver disease, and splenomegaly. Schistosomes are trematodes, or flukes, but they are more cylindrical than flat. They are often called blood flukes Once inside the host, it coats its outer surface with proteins from the host's bloodstream, basically "cloaking" itself from the host defense system. This coat reduces its surface antigenicity and allows it to remain in the host indefinitely. The cycle begins when infected humans release eggs into irrigated fields or ponds, either by deliberate fertilization with excreta or by defecating or urinating directly into the water. The egg hatches in the water and gives off an actively swimming ciliated larva called a miracidium, which instinctively swims to a snail and burrows into a vulnerable site, shedding its ciliated covering in the process. In the body of the snail, the miracidium multiplies into a larger, fork-tailed swimming larva called a cercaria. Cercariae are given off by the thousands into the water by infected snails. Upon contact with a human wading or bathing in water, cercariae attach themselves to the skin by ventral suckers and penetrate into hair follicles. They pass into small blood and lymphatic vessels and are carried to the liver. Here, the schistosomes achieve sexual maturity, and the male and female worms remain permanently entwined to facilitate mating. In time, the pair migrates to and lodges in small blood vessels at specific sites. Schistosoma mansoni and S. japonicum end up in the mesenteric venules of the small intestine. While attached to these intravascular sites, the worms feed upon blood, and the female lays eggs that are eventually voided in feces or urine. Praziquantel is the drug treatment of choice. It works by crippling the worms, making them more antigenic and thereby allowing the host immune response to eliminate them.

Urinary Tract Infection

When urine flow is reduced, or bacteria are accidentally introduced into the bladder, an infection of that organ (known as cystitis) can occur. Occasionally, the infection can also affect the kidneys, in which case it is called pyelonephritis. If an infection is limited to the urethra, it is called urethritis. Cystitis is a disease of sudden onset. Symptoms include pain, frequent urges to urinate even when the bladder is empty, and burning pain accompanying urination (called dysuria). The urine can be cloudy due to the presence of bacteria and white blood cells. It may have an orange tinge from the presence of red blood cells (hematuria). Low-grade fever and nausea are frequently present. If back pain is present and fever is high, it is an indication that the kidneys may also be involved (pyelonephritis). Pyelonephritis is a serious infection that can result in permanent damage to the kidneys if improperly or inadequately treated. If only the bladder is involved, the condition is sometimes called acute uncomplicated UTI. When they occur in health care facilities, they are almost always a result of catheterization In 95% of UTIs, the cause is bacteria that are normal biota in the gastrointestinal tract. Escherichia coli is by far the most common of these, accounting for approximately 80% of community-acquired urinary tract infections. Staphylococcus saprophyticus and Enterococcus are also common culprits transmitted from one organ system to another

Cyclospora cayetanensis

an emerging protozoan pathogen that causes chronic diarrhea Its mode of transmission is fecal-oral—though not through the ingestion of cysts themselves Most cases of infection have been effectively controlled with trimethoprim-sulfamethoxazole lasting 1 week. Traditional antiprotozoan drugs are not effective

Ascaris lumbricoides

a giant intestinal roundworm (up to 300 mm—a foot or more—long) that probably accounts for the greatest number of worm infections worldwide spends its larval and adult stages in humans and releases embryonic eggs in feces, which are then spread to other humans through food, drink, or contaminated objects placed in the mouth. The eggs thrive in warm, moist soils and resist cold and chemical disinfectants, but they are sensitive to sunlight, high temperatures, and drying. After ingested eggs hatch in the human intestine, the larvae embark upon an odyssey in the tissues. First, they penetrate the intestinal wall and enter the lymphatic and circulatory systems. They are swept into the heart and eventually arrive at the capillaries of the lungs. From this point, the larvae migrate up the respiratory tree to the glottis. Worms entering the throat are swallowed and returned to the small intestine, where they reach adulthood and reproduce, producing up to 200,000 fertilized eggs a day. Even as adults, male and female worms are not attached to the intestine and retain some of their exploratory ways. They are known to invade the biliary channels of the liver and gallbladder, and on occasion the worms emerge from the nose and mouth. Severe inflammatory reactions mark the migratory route, and allergic reactions such as bronchospasm, asthma, or skin rash can occur. Heavy worm loads can retard the physical and mental development of children (figure 22.24). One factor that contributes to intestinal worm infections is self-reinoculation due to poor personal hygiene.

Trichinosis

an infection transmitted by eating pork (and sometimes other wildlife) that have the cysts of Trichinella species embedded in the meat. The life cycle of this nematode is spent entirely within the body of a mammalian host such as a pig, bear, cat, dog, or rat. In nature, the parasite is maintained in an encapsulated (encysted) larval form in the muscles of these animal reservoirs and is transmitted when other animals prey upon them. The disease cannot be transmitted from one human to another except in the case of cannibalism. The cyst envelope is digested in the stomach and small intestine, which liberates the larvae. After burrowing into the intestinal mucosa, the larvae reach adulthood and mate. The larvae that result from this union penetrate the intestine and enter the lymphatic channels and blood. All tissues are at risk for invasion, but final development occurs when the coiled larvae are encysted in the skeletal muscle. At maturity, the cyst is about 1 mm long and can be observed by careful inspection of meat. Although larvae can deteriorate over time, they have also been known to survive for years. Symptoms may be unnoticeable or they could be life-threatening, depending on how many larvae were ingested in the tainted meat. The first symptoms, when present, mimic influenza or viral fevers, with diarrhea, nausea, abdominal pains, fever, and sweating. The second phase, brought on by the mass migration of larvae and their entrance into muscle, produces puffiness around the eyes, intense muscle and joint pain, shortness of breath, and pronounced eosinophilia. The most serious life-threatening manifestations are heart and brain involvement. Although the symptoms eventually subside, a cure is not available once the larvae have encysted in muscles.

prostatis

an inflammation of the prostate gland The acute form is virtually always caused by bacterial infection. The bacteria are usually normal biota from the intestinal tract or may have caused a previous urinary tract infection. The chronic form is also often caused by bacteria. Researchers have found that the chronic form, often unresponsive to antibiotic treatment, can be caused by mixed biofilms of bacteria in the prostate. Symptoms may include pain in the groin and lower back, frequent urge to urinate, difficulty in urinating, blood in the urine, and painful ejaculation. Acute form is accompanied by fever, chills, and flulike symptoms. Patients appear to be quite ill with the acute form of the disease.

Cysticercosis

caused by Taenia solium This helminth is a tapeworm. Adult worms are usually around 5 meters long and have a scolex with hooklets and suckers to attach to the intestine. Disease caused by T. solium (the pig tapeworm) is distributed worldwide but is mainly concentrated in areas where humans live in close proximity with pigs or eat undercooked pork. In pigs, the eggs hatch in the small intestine and the released larvae migrate throughout the organs. Ultimately, they encyst in the muscles, becoming cysticerci, young tapeworms that are the infective stage for humans. When humans ingest a live cysticercus in pork, the coat is digested and the organism is flushed into the intestine, where it firmly attaches by the scolex and develops into an adult tapeworm. Infection with T. solium can take another form when humans ingest the tapeworm eggs rather than cysticerci. Although humans are not the usual intermediate hosts, the eggs can still hatch in the intestine, releasing tapeworm larvae that migrate to all tissues. They form bladderlike sacs throughout the body that can cause serious damage. Infections with T. solium can take another form when humans ingest the tapeworm eggs rather than infected meat. Then, the human, instead of the tapeworm in the gut, becomes the host of the encysted larvae or cysticerci, leading to a condition called cysticercosis

Chancroid

caused by a pleomorphic gram-negative rod called Haemophilus ducreyi This ulcerative disease usually begins as a soft papule, or bump, at the point of contact. It develops into a "soft chancre" (in contrast to the hard syphilis chancre), which is very painful in men but may be unnoticed in women. Inguinal lymph nodes can become very swollen and tender. It is very common in the tropics and subtropics and is becoming more common in the United States. transmitted exclusively through direct contact and is considered a sexually transmitted infection. This disease is associated with sex workers and poor hygiene; uncircumcised men seem to be more commonly infected than those who have been circumcised. People may carry this bacterium asymptomatically.

Genital herpes

caused by herpes simplex viruses (HSVs). Two types of HSV have been identified, HSV-1 and HSV-2. After initial infection, a person may notice no symptoms. Alternatively, herpes can cause the appearance of single or multiple vesicles on the genitalia, perineum, thigh, and buttocks. The vesicles are small and are filled with a clear fluid. They are intensely painful to the touch. The appearance of lesions the first time one gets them can be accompanied by malaise, anorexia, fever, and bilateral swelling and tenderness in the groin. Occasionally, central nervous system symptoms such as meningitis or encephalitis can develop. Thus, initial infection can be either completely asymptomatic or serious enough to require hospitalization. After recovery from initial infection, a person may have recurrent episodes of lesions. In most cases, patients remain asymptomatic or experience recurrent "surface" infections indefinitely. Very rarely, complications can occur. Every year, one or two persons per million with chronic herpes infections develop encephalitis. The virus disseminates along nerve pathways to the brain (although it can also infect the spinal cord). The effects on the central nervous system begin with headache and stiff neck and can progress to mental disturbances and coma. The fatality rate in untreated encephalitis cases is 70%, although treatment with acyclovir is effective. Patients with underlying immunodeficiency are more prone to severe, disseminated herpes infection than are immunocompetent patients. Of greatest concern are patients receiving organ grafts, cancer patients on immunosuppressive therapy, those with congenital immunodeficiencies, and AIDS patients. Recent data suggest that people with HSV-1 are more prone to Alzheimer's disease, particularly if they carry a particular variant of a particular gene in the neonate and the fetus Page 717(figure 23.17), HSV infections are very destructive and can be fatal. Most cases occur when infants are contaminated by the mother's reproductive tract immediately before or during birth, but they have also been traced to hand transmission from the mother's lesions to the baby HSV-1 is thought of as a virus that infects the oral mucosa, resulting in "cold sores" or "fever blisters," and HSV-2 is thought of as the genital virus. In reality, either virus can infect either region, depending on the type of contact that transmits the infectious agent. have a tendency to become latent. During latency, some type of signal causes most of the HSV genome not to be transcribed. This allows the virus to be maintained within cells of the nervous system between episodes

Candida Albicans

causes vaginitis, an inflammation of the vagina The vaginal condition caused by this fungus is known as a yeast infection. The yeast is easily detectable on a wet prep or a Gram stain of material obtained during a pelvic exam In otherwise healthy people, the fungus is not invasive and limits itself to this surface infection. However, infections of the bloodstream do occur and have high mortality rates. They do not normally stem from vaginal infections with the fungus, however, and are seen most frequently in hospitalized patients. AIDS patients are also at risk of developing systemic infections. Vaginal infections with this organism are nearly always opportunistic

Pneumocystis jiroveci

most frequent opportunistic infection in AIDS patients, most of whom will develop one or more episodes during their lifetimes. In people with intact immune defenses, it is usually held in check by lung phagocytes and lymphocytes, but in those with deficient immune systems, it multiplies intracellularly and extracellularly. The massive numbers of fungi adhere tenaciously to the lung pneumocytes and cause an inflammatory condition. The lung epithelial cells slough off, and a foamy exudate builds up. Symptoms are nonspecific and include cough, fever, shallow respiration, and cyanosis Inhalation of spores is probably common

vaginosis

most likely a result of a reduction in the number of "good bacteria" (lactobacilli) in the vagina can lead to complications such as pelvic inflammatory disease (PID), infertility, and, more rarely, ectopic pregnancies. Babies born to some mothers with this have low birthweights. not considered to be sexually transmitted, but very common in sexually active women some cells will appear to be nearly covered with adherent bacteria. (In normal times, vaginal epithelial cells are sparsely covered with bacteria.) These cells are called clue cells and are a helpful diagnostic indicator. They can also be found on Pap smears.

Trichomonas vaginalis

seems to cause asymptomatic infections in approximately 50% of females and males, despite its species name. Trichomonads are considered asymptomatic infectious agents rather than normal biota because of evidence that some people experience long-term negative effects. Many cases are asymptomatic, and men seldom have symptoms. Women often have vaginitis symptoms, which can include a white to green, frothy discharge Chronic infection can make a person more susceptible to other infections, including HIV. Also, women who become infected during pregnancy are predisposed to premature labor and low birth weight infants. Chronic infection may also lead to infertility. easily transmitted through sexual contact. It has been called the most common nonviral sexually transmitted infection

Hymenolepis species

small tapeworms and are the most common human tapeworm infections in the world. There are two species: H. nana, known as the dwarf tapeworm because it is only 15 to 40 mm in length H. diminuta, the rat tapeworm, which is usually 20 to 60 cm in length as an adult

entamoeba histolytica

secretes enzymes that dissolve tissues, and it actively penetrates deeper layers of the mucosa, leaving erosive ulcerations. This phase is marked by dysentery (bloody, mucus-filled stools), abdominal pain, fever, diarrhea, and weight loss. The most life-threatening manifestations of intestinal infection are hemorrhage, perforation, appendicitis, and tumorlike growths called amebomas. Lesions in the mucosa of the colon have a characteristic flasklike shape. Extraintestinal infection occurs when amoebas invade the viscera of the peritoneal cavity. The most common site of invasion is the liver. Here, abscesses containing necrotic tissue and trophozoites develop and cause amoebic hepatitis. Another, rarer complication is pulmonary amoebiasis. Other infrequent targets of infection are the spleen, adrenals, kidney, skin, and brain. Severe forms of the disease result in about a 10% fatality rate. Amoebiasis begins when viable cysts are swallowed and arrive in the small intestine, where the alkaline pH and digestive juices of this environment stimulate excystment. Each cyst releases four trophozoites, which are swept into the cecum and large intestine. There, the trophozoites attach by fine pseudopods, multiply, actively move about, and feed harbored by chronic carriers whose intestines favor the encystment stage of the life cycle. Cyst formation cannot occur in active dysentery because the feces are so rapidly flushed from the body, but after recuperation, cysts are continuously shed in feces. Humans are the primary hosts of E. histolytica. Infection is usually acquired by ingesting food or drink contaminated with cysts released by an asymptomatic carrier. Diagnosis of this protozoal infection relies on a combination of tests, including microscopic examination of stool for the characteristic cysts or trophozoites, ELISA tests of stool for E. histolytica antigens, and serological testing for the presence of antibodies to the pathogen

Human Papillomavirus

the causative agent of genital warts a group of nonenveloped DNA viruses belonging to the Papovaviridae family. There are more than 100 different types of HPV. Some types are specific for the mucous membranes; others invade the skin. Some of these viruses are the cause of plantar warts, which often occur on the soles of the feet. Other HPVs cause the common or "seed" warts and flat warts. Symptoms, if present, may manifest as warts—outgrowths of tissue on the genitals. In females, these growths can occur on the vulva and in and around the vagina. In males, the warts can occur in or on the penis and the scrotum. In both sexes, the warts can appear in or on the anus and even on the skin around the groin, such as the area between the thigh and the pelvis. The warts themselves range from tiny, flat, inconspicuous bumps to extensively branching, cauliflower-like masses called condyloma acuminata. The warts are unsightly and can be obstructive, but they do not generally lead to more serious symptoms. Certain types of the virus infect cells on the female cervix. This infection may be "silent," or it may lead to abnormal cell changes in the cervix. Some of these cell changes can eventually result in malignancies of the cervix. The vast majority of cervical cancers are caused by HPV infection. (It is possible that chronic infections with other microorganisms cause a very small percentage of cervical malignancies.) The major virulence factors for cancer-causing HPVs are oncogenes, which code for proteins that interfere with normal host cell function, resulting in uncontrolled growth. The Pap smear is still the single best screening procedure available for cervical cancer

Chlamydia

the most common reportable infectious disease in the United States C. trachomatis is a very small, gram-negative bacterium. It lives inside host cells as an obligate intracellular parasite. ability to grow intracellularly contributes to its virulence because it escapes certain aspects of the host's immune response. Also, the bacterium has a unique cell wall that apparently prevents the phagosome from fusing with the lysosome inside phagocytes. majority of cases are asymptomatic Males - the bacterium causes an inflammation of the urethra. The symptoms mimic gonorrhea—namely, discharge and painful urination. Untreated infections may lead to epididymitis. Females - cervicitis, a discharge, and often salpingitis. Pelvic inflammatory disease is a frequent sequela of female Chlamydia infection. A woman is even more likely to experience PID as a result of a Chlamydia infection than as a result of gonorrhea. Infection with this microorganism is usually detected initially using a rapid technique such as PCR or ELISA. Direct fluorescent antibody detection is also used. Serology is not always reliable. Isolating the bacterium and growing it in cell culture is the best method for detecting this bacterium, but because it is time-consuming and expensive, it is performed only in cases where 100% accuracy is required—such as in rape or child abuse cases. A urine test is available, which has definite advantages for widespread screening, but it is slightly less accurate for females than males.

LaCrosse Virus

this arbovirus is a neuroinvasive disease that has only been reported in the eastern half of the United States and Texas. It is maintained by infection of small mammals, such as squirrels and chipmunks, and mosquitoes. The neuroinvasive form of the disease occurs primarily in children under 16. It is rarely fatal.

Opisthorchis sinensis and Clonorchis sinensis

two worms known as Chinese liver flukes. They complete their sexual development in mammals such as humans, cats, dogs, and swine. Their intermediate development occurs in snail and fish hosts. Humans ingest metacercariae in inadequately cooked or raw freshwater fish Larvae hatch and crawl into the bile duct, where they mature and shed eggs into the intestinal tract. Feces containing eggs are passed into standing water that harbors the intermediate snail host. The cycle is complete when infected snails release cercariae that invade fish living in the same water. Symptoms of infection are slow to develop but include thickening of the lining of the bile duct and possible granuloma formation in areas of the liver if eggs enter the stroma of the liver. If the infection is heavy, the bile duct can be blocked.

periodontal disease

97% to 100% of the population have some manifestation of it by age 45. Most kinds are due to bacterial colonization and varying degrees of inflammation that occur in response to gingival damage. Microbes from pets have also been implicated in periodontal disease initial stage is *gingivitis*, the signs of which are swelling, loss of normal contour, patches of redness, and increased bleeding of the gingiva. Spaces or pockets of varying depth also develop between the tooth and the gingiva. If this condition persists, a more serious disease called *periodontitis* results. This is the natural extension of the disease into the periodontal membrane and cementum. The deeper involvement increases the size of the pockets and can cause bone resorption severe enough to loosen the tooth in its socket. If the condition is allowed to progress, the tooth can be lost plaque accumulating in the gingival sulcus cause abrasions in the delicate gingival membrane, and the chronic trauma causes a pronounced inflammatory reaction. with high numbers of the bacteria associated with periodontitis also have thicker carotid arteries and increased rates of cardiovascular disease, further supporting the systemic effects of oral inflammation. Regular brushing and flossing to remove plaque automatically reduce both caries and calculus production. Once calculus has formed on teeth, it cannot be removed by brushing but can be dislodged only by mechanical procedures (scaling) in the dental office.

Creutzfeldt-Jakob disease (CJD)

A spongiform encephalopathy caused by infection with a prion. The disease is marked by dementia, impaired senses, and uncontrollable muscle contractions. Symptoms of all forms include altered behavior, dementia, memory loss, impaired senses, delirium, and premature senility. Uncontrollable muscle contractions continue until death, which usually occurs within 1 year of diagnosis. It is thought that 10% to 15% of CJD cases are due to an inherited mutation within a single gene. These are termed familial or hereditary CJD a protein called PrPC that spontaneously transforms into a nonfunctional form in CJD. This altered protein (PrPSC), which he termed a prion, triggers damage in the brain and other areas of the central nervous system. The PrPSC actually becomes catalytic and able to spontaneously convert other normal human PrPC proteins into the abnormal form. This becomes a self-propagating chain reaction that creates a massive accumulation of PrPSC, leading to plaques, spongiform damage (that is, holes in the brain), and severe loss of brain function. Hereditary CJD and sporadic CJD are most common in elderly people

trench fever

Bartonella quintana is carried by lice. The feces of the lice contain the bacterium, and transmission usually occurs when the feces enter the bite wound Highly variable symptoms can include a 5- to 6-day fever (the species epithet, quintana, refers to a 5-day fever). Symptoms also include leg pains, especially in the tibial region (the disease is sometimes called "shinbone fever"); headache; chills; and muscle aches. A macular rash can also occur. Endocarditis can develop, especially in the urban version of the disease. The microbe can persist in the blood long after convalescence and is responsible for later relapses.

sinusitis

Commonly called a sinus infection, this inflammatory condition of any of the four pairs of sinuses in the skull can actually be caused by allergy (most common) or infections. The infectious agents that may be responsible for the condition include a variety of viruses or bacteria and, less commonly, fungi. Infections of the sinuses often follow a bout with the common cold. The inflammatory symptoms of a cold produce a large amount of fluid and mucus, and when trapped in the sinuses, these secretions provide an excellent growth medium for bacteria or fungi. This is why it is common for patients suffering from the common cold to then develop sinusitis caused by bacteria or fungi. typically experiences nasal congestion, pressure above the nose or in the forehead, and sometimes the feeling of a headache or a toothache. Facial swelling and tenderness are common. Discharge from the nose and mouth appears opaque and may have a green or yellow color in the case of bacterial infections. Viral infections are less likely to produce colored discharge. Discharge caused by an allergy is usually clear, and the symptoms may be accompanied by itchy, watery eyes. Viral infection is probably the most common cause Many cases are caused by Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, Corynebacterium tuberculostearicum, and Haemophilus influenzae. The causative organism is usually not identified, but treatment is begun empirically, based on the symptoms. (not a communicable disease.) Simple fungal infections may normally be found in the maxillary sinuses and are noninvasive in nature. These colonies are generally not treated with antifungal agents but instead are simply mechanically removed by a physician. Aspergillus fumigatus is a common fungus involved in this type of infection, but Bipolaris species are an emerging cause of fungal sinusitis today.

Gastritis

Pain and/or nausea, usually experienced after eating; result of inflammation of the lining of the stomach. experienced as sharp or burning pain emanating from the abdomen. caused by Helicobacter pylori, a curved, gram-negative rod transmitted from person to person by the oral-oral or fecal-oral route. It seems to be acquired early in life mainly through what is called "familial transfer"—the microbe is acquired from family members, especially from infected mothers to their children. Gastric or peptic ulcers are actual lesions in either the mucosa of the stomach (gastric ulcers) or in the uppermost portion of the small intestine (duodenal ulcers). Severe ulcers can be accompanied by bloody stools, vomiting, or both. The symptoms are often worse at night, after eating, or under conditions of psychological stress. The urea breath test is a noninvasive method that is sometimes used. In this test, patients ingest urea that has a radioactive tag on its carbon molecule. If Helicobacter is present in a patient's stomach, the bacterium's urease breaks down the urea and the patient exhales radioactively labeled carbon dioxide. In the absence of urease, the intact urea molecule passes through the digestive system. Patients whose breath is positive for the radioactive carbon are considered positive for Helicobacter.

malaria

Plasmodium species are protozoans in the sporozoan group. They are apicomplexans, which live in animal hosts and lack locomotor organelles in the mature state spread primarily by the female Anopheles mosquito and occasionally by shared hypodermic needles and blood transfusions. the first symptoms are malaise, fatigue, vague aches, and nausea with or without diarrhea, followed by bouts of chills, fever, and sweating. These symptoms occur at 48- or 72-hour intervals, as a result of the synchronous rupturing of red blood cells. The interval, length, and regularity of symptoms reflect the type of malaria Patients with falciparum ____________, the most virulent type, often manifest persistent fever, cough, and weakness for weeks without relief. Complications are hemolytic anemia from lysed blood cells and organ enlargement and rupture due to cellular debris that accumulates in the spleen, liver, and kidneys. One of the most serious complications of falciparum _________________ is termed cerebral ___________. In this condition, small blood vessels in the brain become obstructed due to the increased ability of red blood cells (RBCs) to adhere to vessel walls (a condition called cytoadherence induced by the infecting protozoan). Plasmodium also metabolizes glucose at a very high rate, leading to hypoglycemia in the human host. The damage to RBCs results in anemia highest death rate in the acute phase, especially in children

brucellosis

The Brucella species responsible for this disease live in phagocytic cells. These cells carry the bacteria into the bloodstream, creating focal lesions in the liver, spleen, bone marrow, and kidney contains tiny, aerobic gram-negative coccobacilli enters through damaged skin or via mucous membranes of the digestive tract, conjunctiva, and respiratory tract. It is associated predominantly with occupational contact in slaughterhouses, livestock handling, and the veterinary profession. Infection takes place through contact with blood, urine, and placentas and through consumption of raw milk and cheese. Human-to-human transmission is rare, but brucellosis is considered the most common laboratory-acquired infection. The patient's history can be very helpful in diagnosis, as are serological tests of the patient's blood and blood culture of the pathogen. In areas where Brucella is endemic, serology is of limited use because significant proportions of the population already display antibodies to the bacterium. Blood culture is the gold standard. PCR-based testing is available but not yet reliable enough. Prevention is achieved by testing and elimination of infected animals, quarantine of imported animals, and pasteurization of milk.

Escherichia coli

The K1 strain of Escherichia coli is the second most common cause of neonatal meningitis. Most babies who suffer from this infection are premature, and their prognosis is poor. 20% of them die, even with aggressive antibiotic treatment, and those who survive often have brain damage. The bacterium is usually transmitted from the mother's birth canal. It causes no disease in the mothers but can infect the vulnerable tissues of a neonate. It seems to have a predilection for the tissues of the central nervous system. Ceftazidime or cefepime +/- gentamicin is usually administered intravenously

acute endocarditis

most often the result of an overwhelming bloodstream challenge with bacteria. Some of these bacteria seem to have the ability to colonize normal heart valves. Accumulations of bacteria on the valves (vegetations) hamper their function and can lead directly to cardiac malfunction and death. Alternatively, pieces of the bacterial vegetation can break off and create emboli (blockages) in vital organs. most often caused by Staphylococcus aureus most common route of transmission is parenteral—that is, via direct entry into the body. Intravenous or subcutaneous drug users are a significant risk group for the condition. The heroin epidemic currently sweeping the United States has led to a large increase in the incidence of acute endocarditis, usually caused by Staphylococcus aureus.

Naegleria fowleri

This trophozoite is a small, flask-shaped amoeba that moves by means of a single, broad pseudopod. It can form a rounded, thick-walled cyst that is resistant to temperature extremes and mild chlorination. Most cases of infection reported worldwide occur in people who have been swimming in warm, natural bodies of freshwater. Infection can begin when amoebas are forced into human nasal passages as a result of swimming, diving, or other aquatic activities. The amoeba infects the olfactory epithelium and utilizes the olfactory nerve to travel to the brain. Infection then spreads as the pathogen enters the fluid-filled subarachnoid space, making diagnosis from CSF possible. The result is primary amoebic meningoencephalitis (PAM), a rapid, massive destruction of brain and spinal tissue that causes hemorrhage and coma and invariably ends in death within a week of onset

African Sleeping Sickness

This condition is caused by Trypanosoma brucei, a member of the protozoan group known as hemoflagellates because of their propensity to live in the blood and tissues of the human host Trypanosoma brucei is a flagellated protozoan, an obligate parasite that is spread by a blood-sucking insect called the tsetse fly, which serves as its intermediate host. It shares a complicated life cycle with other hemoflagellates. T. brucei gambiense is found in west and central Africa, is associated with chronic disease, and accounts for over 95% of total reported cases T. brucei rhodesiense is found in eastern and southern Africa. occurs only in sub-Saharan Africa Symptoms include intermittent fever, enlarged spleen, swollen lymph nodes, and joint pain. There are two variants of the disease, caused by two different subspecies of the protozoan. In both forms, the central nervous system is affected, the initial signs being personality and behavioral changes that progress to extreme fatigue and sleep disturbances. The disease is commonly called sleeping sickness but, in fact, uncontrollable sleepiness occurs primarily in the day and is followed by sleeplessness at night

Rocky Mountain Spotted Fever (RMSF)

This disease is named for the region in which it was first detected in the United States—the Rocky Mountains of Montana and Idaho. In spite of its name, the disease occurs infrequently in the western United States. The majority of cases are concentrated in the Southeast and eastern seaboard regions. caused by a bacterium called Rickettsia rickettsii, which is transmitted by hard ticks such as the wood tick (Dermacentor andersoni), the American dog tick (D. variabilis, among others), and the Lone Star tick (Amblyomma americanum). The dog tick is probably most responsible for transmission to humans because it is the major vector in the southeastern United States. the first symptoms are sustained fever, chills, headache, and muscular pain. A distinctive, spotted rash usually comes on within 2 to 4 days after the prodrome and develops first on the wrists, forearms, and ankles before spreading to other areas of the body. Early lesions are slightly mottled, like measles, but later ones are macular, maculopapular, and even petechial. In the most severe untreated cases, the enlarged lesions merge and can become necrotic, predisposing to gangrene of the toes or fingertips.

Coccidioides

This fungus causes a condition that is often called "Valley Fever" in the American Southwest. The morphology is very distinctive. At 25°C, it forms a moist white to brown colony with abundant, branching, septate hyphae. These hyphae fragment into thick-walled, blocklike arthroconidia (arthrospores) at maturity. On special media incubated at 37°C to 40°C, an arthrospore germinates into the parasitic phase, a small, spherical cell called a spherule that can be found in infected tissues as well. This structure swells into a giant sporangium that cleaves internally to form numerous endospores that look like bacterial endospores but lack their resistance traits. Conditions favoring its settlement include high carbon and salt content and a semiarid, relatively hot climate. The fungus has been isolated from soils, plants, and a large number of vertebrates. The natural history of the fungus follows a cyclic pattern—a period of dormancy in winter and spring, followed by growth in summer and fall. Growth and spread are greatly increased by cycles of drought and heavy rains.

Acanthamoeba

This protozoan is characterized by a large, amoeboid trophozoite with spiny pseudopods and a double-walled cyst. It differs from Naegleria in its portal of entry; it invades broken skin, the conjunctiva, and occasionally the lungs and urogenital epithelia. Although it causes a meningoencephalitis somewhat similar to that of Naegleria, the course of infection is lengthier. The disease is called granulomatous amoebic meningoencephalitis (GAM) and has only a 2% to 3% survival rate.

Streptococcus agalactiae

This species of Streptococcus belongs to the Lancefield group B of the streptococci. It colonizes 10% to 30% of female genital tracts and is the most frequent cause of neonatal meningitis. The treatment for neonatal disease is intravenous penicillin G, sometimes supplemented with an aminoglycoside.

plague

Three possible manifestations of infection occur with the bacterium causing plague. 1. pneumonic plague - The acute, frequently fatal form of pneumonia caused by Yersinia pestis; a respiratory disease. 2. bubonic plague - The form of plague in which bacterial growth is primarily restricted to the lymph and is characterized by the appearance of a swollen lymph node referred to as a bubo; the bacterium, which is injected by the bite of a flea, enters the lymph and is filtered by a local lymph node 3. septicemic plague - A form of infection with Yersinia pestis occurring mainly in the bloodstream and leading to high mortality rates. hosts spread the disease to other mammals, called amplifying hosts, that become infected with the bacterium and experience massive die-offs during epidemics. because death can occur as quickly as 2 to 4 days after the appearance of symptoms, prompt diagnosis and treatment of plague are imperative. Culture of the organism is the definitive method of diagnosis, although a Gram stain of aspirate from buboes often reveals the presence of the safety-pin-shaped bacteria.

Arboviruses

Wherever there are arthropods (insects and ticks), there are also _____________________, so collectively their distribution is worldwide. Peak incidence of infection typically occurs when the arthropod is actively feeding and reproducing, usually from late spring through early fall. Warm-blooded vertebrates also maintain the virus during the cold and dry seasons. Humans can serve as dead-end, accidental hosts, as in equine encephalitis, or they can be a maintenance reservoir, as in yellow fever ________________________ encephalitis begins with an arthropod bite, releasing the virus into the bloodstream, where it will travel to nearby lymphoid tissues for replication The patient's history of travel to endemic areas or contact with vectors, along with serum analysis, helps with the diagnosis. Most of the control safeguards for ________________ disease are aimed at the arthropod vectors. Mosquito abatement by the elimination of breeding sites and the broad use of insecticides has been highly effective in restricted urban settings. Birds play a role as reservoirs of the virus, but direct transmission between birds and humans does not appear to occur.

pneumonia

a classic example of an anatomical diagnosis. It is defined as an inflammatory condition of the lung in which fluid fills the alveoli Bacteria and a wide variety of viruses can cause this kills more children than any other infectious disease in the world today usually begin with upper respiratory tract symptoms, including congestion. Headache is common. Fever is often present, and the onset of lung symptoms follows. These Page 635symptoms are chest pain, fever, cough, and the production of discolored sputum. Because of the pain and difficulty of breathing, the patient appears pale and presents an overall sickly appearance. The severity and speed of onset of the symptoms vary according to the etiologic agent.

Cryptococcus neoformans

a fungus that causes a more chronic form of meningitis with a more gradual onset of symptoms, although in AIDS patients the onset may be fast and the course of the disease more acute. It is sometimes classified as a meningoencephalitis (inflammation of both brain and meninges). Headache is the most common symptom, but nausea and neck stiffness are very common. This fungus is a widespread resident of human habitats. It has a spherical to ovoid shape, with small, constricted buds and a large capsule that is important in its pathogenesis Masses of dried yeast cells are readily scattered into the air and dust. Its role as an opportunist is supported by evidence that healthy humans have strong resistance to it and that clinically obvious infection occurs primarily in debilitated patients By far the highest rates of cryptococcal meningitis occur among patients with AIDS. This meningitis is frequently fatal. Other conditions that predispose individuals to infection are steroid treatment, diabetes, and cancer. It is not considered communicable among humans can be diagnosed via negative staining of specimens to detect encapsulated budding yeast cells that do not occur as pseudohyphae. Rapid tests, such as the cryptococcal antigen test, have largely replaced this method of disease diagnosis in many labs.

Cronobacter sakazakii

a gram-negative bacillus found mainly in the environment, it can survive very dry conditions. It has been implicated in outbreaks of neonatal and infant meningitis transmitted through contaminated powdered infant formula. Although cases of Cronobacter meningitis are rare, mortality rates can reach 40%. The FDA and the CDC advise hospitals to use ready-to-feed or concentrated liquid formulas and that home caregivers make fresh formula for each feeding and discard any leftover formula.

Haemophilus influenzae

a gram-negative coccobacillus that causes one of the most severe forms of meningitis in humans. Humans are the only known reservoir, and the portal of entry for this bacterium is the nasopharynx Routine vaccination with one of two subunit vaccines (both contain capsular polysaccharide conjugated to a protein) is recommended for all children, beginning at age 2 months, with the recommendation of a follow-up booster dose a very common cause of severe meningitis and death

Listeria monocytogenes

a gram-positive bacterium that ranges in morphology from coccobacilli to long filaments in palisade formation. Cells do not produce capsules or endospores and have from one to four flagella. is not fastidious and is resistant to cold, heat, salt, pH extremes, and bile. It grows inside host cells and can move directly from an infected host cell to an adjacent healthy cell. The death rate is around 20%. Pregnant women are especially susceptible to infection, which can be transmitted to the infant prenatally when the microbe crosses the placenta or postnatally through the birth canal. Intrauterine infections are systemic and usually result in premature abortion and fetal death. Most cases are associated with ingesting contaminated dairy products, poultry, and meat. Prevention can be improved by adequate pasteurization temperatures and by proper washing, refrigeration, and cooking of foods that are suspected of being contaminated with animal manure or sewage. The U.S. Food and Drug Administration cautions pregnant women not to eat soft, unpasteurized cheeses or deli meats unless they are cooked.

Tetanus

a neuromuscular disease whose alternate name, lockjaw, refers to an early effect of the disease on the jaw muscle. The etiologic agent, Clostridium tetani, is a common resident of soil and the gastrointestinal tracts of animals. It is a gram-positive, endospore-forming rod. The endospores it produces often swell the vegetative cell but are only produced under anaerobic conditions. C. tetani releases a powerful neurotoxin, tetanospasmin, that binds to target sites on peripheral motor neurons, on the spinal cord and brain, and in the sympathetic nervous system. The toxin acts by blocking the inhibition of muscle contraction. Without inhibition of contraction, the muscles contract uncontrollably, resulting in spastic paralysis. The first symptoms are clenching of the jaw, followed in succession by extreme arching of the back, flexion of the arms, and extension of the legs Lockjaw confers the bizarre appearance of risus sardonicus (sardonic grin), which looks eerily as though the person is smiling. Death most often occurs due to paralysis of the respiratory muscles and respiratory arrest. As the vegetative cells grow, various metabolic products are released into the infection site, including the tetanospasmin toxin. The toxin spreads to nearby motor nerve endings in the injured tissue, binds to them, and travels via axons to the ventral horns of the spinal cord Endospores usually enter the body through accidental puncture wounds, burns, umbilical stumps, frostbite, and crushed body parts Neonatal ____________ still kills 60,000 newborns each year. A majority of infections in these countries are a direct result of unhygienic practices during childbirth, including the use of dung, ashes, or mud to arrest bleeding or for religious purposes during this process. treatment is aimed at deterring the degree of toxemia and infection and maintaining patient homeostasis

hepatitis A

a nonenveloped, single-stranded RNA enterovirus. It belongs to the family Picornaviridae far milder and shorter-term than the other forms. accompanied by vague, flulike symptoms. Darkened urine is often seen in this and other hepatitises. Jaundice is present in only about 10% of the cases. generally of low virulence. Most of the pathogenic effects are thought to be the result of host response to the presence of virus in the liver spread through the fecal-oral route (and is sometimes known as infectious hepatitis) Most of these are a result of close institutional contact, unhygienic food handling, consumption of shellfish, sexual transmission, or travel to other countries. Diagnosis of the disease is aided by detection of anti-HAV IgM antibodies produced early in the infection and by tests to identify HA antigen or virus directly in stool samples. Prevention is based primarily on immunization

HIV/AIDS

a retrovirus in the genus Lentivirus They are named "retroviruses" because they reverse the usual order of transcription. They contain an unusual enzyme called reverse transcriptase (RT) that catalyzes the replication of double-stranded DNA from single-stranded RNA. There are two major types of HIV—namely HIV-1, which is the dominant form in most of the world, and HIV-2. Genetic sequencing of HIV-1 shows that it is most related to simian immunodeficiency viruses in chimpanzees, while HIV-2 evolved from related viruses in sooty mangabeys, a type of monkey found in Africa. Both highlight the evidence that HIV in humans was derived from a zoonotic primate virus. Because the blood of HIV-infected individuals harbors high levels of free virus in both very early and very late stages of infection and high levels of infected leukocytes throughout infection, any form of intimate contact involving transfer of blood (trauma, needle sharing) can be a potential source of infection. Semen and vaginal secretions also harbor free virus and infected white blood cells; thus, they are significant factors in sexual transmission.

Rabies

a slow, progressive zoonotic disease characterized by fatal encephalitis. It is distributed nearly worldwide, except for perhaps two dozen countries that have remained rabies-free by practicing rigorous animal control. The average incubation period is 1 to 2 months or more, depending on the wound site, its severity, and the inoculation dose "furious" - the first acute signs of neurological involvement are periods of agitation, disorientation, seizures, and twitching. Spasms in the neck and pharyngeal muscles lead to severe pain upon swallowing, leading to a symptom known as hydrophobia (fear of water). Throughout this phase, the patient is fully coherent and alert. "dumb" - a patient is not hyperactive but is paralyzed, disoriented, and stuporous. Ultimately, both forms progress to the coma phase, resulting in death from cardiac or respiratory arrest

Legionella pneumophila

a weakly gram-negative bacterium that displays a range of shapes, from coccus to filaments widely distributed in aqueous habitats as diverse as tap water, cooling towers, spas, ponds, and other freshwaters thought of as an opportunistic disease, usually affecting elderly people and rarely being seen in children and healthy adults. It is difficult to diagnose, even with specific antibody tests. It is not transmitted person to person.

anthrax

a zoonotic disease of herbivorous livestock (sheep, cattle, and goats) Bacillus anthracis is a gram-positive, endospore-forming rod that is among the largest of all bacterial pathogens. a facultative parasite that undergoes its cycle of vegetative growth and sporulation in the soil. Animals become infected while grazing on grass contaminated with endospores. The main virulence factor of B. anthracis is what is referred to as a "tripartite" toxin can exhibit its primary symptoms in various locations of the body: on the skin, in the lungs (two most common), in the gastrointestinal tract, and in the central nervous system

Tularemia

a zoonotic disease that is endemic throughout the Northern Hemisphere. After an incubation period ranging from a few days to 3 weeks, acute symptoms of headache, backache, fever, chills, malaise, and weakness appear. Further clinical manifestations are tied to the portal of entry. They include ulcerative skin lesions, swollen lymph glands, conjunctival inflammation, sore throat, intestinal disruption, and pulmonary involvement. caused by a facultative intracellular gram-negative bacterium called Francisella tularensis abundantly distributed through numerous animal reservoirs and vectors in northern Europe, Asia, and North America but not in the tropics. This disease is noteworthy for its complex epidemiology and spectrum of symptoms. Although rabbits and rodents (muskrats and ground squirrels) are the chief reservoirs, other wild animals (skunks, beavers, foxes, opossums) and some domestic animals are implicated as well. The chief route of transmission in the past had been through the activity of skinning rabbits, but with the decline of rabbit hunting, transmission via tick bites is more common

Subacute Endocarditis

almost always preceded by some form of damage to the heart valves or by congenital malformation. Most commonly caused by bacteria of low pathogenicity, often originating in the oral cavity. - Alpha-hemolytic streptococci, such as Streptococcus sanguinis, S. oralis, and S. mutans, are most often responsible, although normal biota from the skin and other bacteria can also colonize abnormal valves and lead to this condition The average age of onset for subacute endocarditis had increased in recent decades from the mid-20s to the mid-50s. Males are more likely to experience it than females.

Poliomyelitis

an acute enteroviral infection of the spinal cord that can cause neuromuscular paralysis. Because it often affects small children, in the past it was called infantile paralysis. Being neurotropic, the virus infiltrates the motor neurons of the anterior horn of the spinal cord, although it can also attack spinal ganglia, cranial nerves, and motor nuclei. Depending on the level of damage to motor neurons, paralysis of the muscles of the legs, abdomen, back, intercostals, diaphragm, pectoral girdle, and bladder can result. In rare cases of bulbar __________________, the brain stem, medulla, or even cranial nerves are affected. This situation leads to loss of control of cardiorespiratory regulatory centers, requiring mechanical respirators The mainstay of polio prevention is vaccination as early in life as possible, usually in four doses starting at about 2 months of age. Adult candidates for immunization are travelers and members of the armed forces. The two forms of vaccine currently in use are inactivated poliovirus vaccine (IPV), developed by Jonas Salk in 1954, and oral poliovirus vaccine (OPV), developed by Albert Sabin in the 1960s.

chikungunya

an alphavirus transmitted by Aedes albopictus mosquitoes. Symptoms are similar to dengue fever with the additional complication of severe joint pain, sometimes lasting for years, and occasional neurological impairment. There is growing concern about this virus, since mosquitoes carrying it showed up in Western Europe (in 2007) and in New York City soon after. In 2014 locally transmitted cases were found in the United States (in Florida and in Puerto Rico). As many as 700 cases in the United States in 2015 were found in persons who had traveled to endemic areas. The virus was not found in South or Central America until 2013; since then, there have been more than 1.7 million cases there.

hepatitis B

an enveloped DNA virus in the family Hepadnaviridae. Intact viruses are often called Dane particles. In addition to the direct damage to liver cells, the spectrum of hepatitis disease may include fever, chills, malaise, anorexia, abdominal discomfort, diarrhea, and nausea. Rashes may appear and arthritis may occur known to be a cause of hepatocellular carcinoma Some patients are coinfected with a particle called the delta agent, sometimes also called a hepatitis D virus. This agent seems to be a defective RNA virus that cannot produce infection unless a cell is also infected with HBV. Even a minute amount of blood (a millionth of a milliliter) can transmit infection. The abundance of circulating virions is so high and the minimal dose so low that such simple practices as sharing a toothbrush or a razor can transmit the infection. also been detected in semen and vaginal secretions, and it can be transmitted by these fluids. Growing concerns about virus spread through donated organs and tissue are prompting increased testing prior to surgery. Spread of the virus by means of close contact in families or institutions is also well documented. risk is highest among people living under crowded conditions, drug addicts, the sexually promiscuous, and those in certain occupations, including people who conduct medical procedures involving blood or blood products. Tattooing and ear or body piercing can expose a person to infection if the instruments are not properly sterilized.

staphylococcus aureus exotoxin

an exotoxin that causes acute diarrhea with vomiting and food poisoning associated with eating foods such as custards, sauces, cream pastries, processed meats, chicken salad, or ham that have been contaminated by handling and then left unrefrigerated for a few hours. Because of the high salt tolerance of S. aureus, even foods containing salt as a preservative are not exempt. The toxins produced by the multiplying bacteria do not noticeably alter the food's taste or smell. The exotoxin (which is an enterotoxin, meaning that it acts on the enteric, or gastrointestinal, system) is heat-stable; inactivation requires 100°C for at least 30 minutes. Thus, heating the food after toxin production may not prevent disease. acts upon the gastrointestinal epithelium and stimulates nerves, with acute symptoms of cramping, nausea, vomiting, and diarrhea. Recovery is also rapid, usually within 24 hours. The disease is not transmissible person to person. Often, a single source will contaminate several people, leading to a small point-source outbreak.

clostridium perfringens

an exotoxin that causes acute diarrhea with vomiting and food poisoning sporulating gram-positive bacterium that causes intestinal symptoms Those most frequently implicated in disease are animal flesh (meat, fish) and vegetables such as beans that have not been cooked thoroughly enough to destroy endospores. When these foods are cooled, endospores germinate and the germinated cells multiply, especially if the food is left unrefrigerated. If the food is eaten without adequate reheating, live C. perfringens cells enter the small intestine and release exotoxin. The toxin, acting upon epithelial cells, initiates acute abdominal pain, diarrhea, and nausea in 8 to 16 hours. Recovery is rapid, and deaths are rare

bacillus cereus exotoxin

an exotoxin that causes acute diarrhea with vomiting and food poisoning the organism is a sporulating gram-positive bacterium that is naturally present in soil. As a result, it is a common resident on vegetables and other products in close contact with soil. It produces two exotoxins, one of which causes a diarrheal-type disease and the other of which causes an emetic, or vomiting, disease. The type of disease that takes place is influenced by the type of food that is contaminated by the bacterium. Emetic - most frequently linked to fried rice, especially when it has been cooked and kept warm for long periods of time. These conditions are apparently ideal for the expression of the low-molecular-weight, heat-stable exotoxin having an emetic effect. Diarrheal - usually associated with cooked meats or vegetables that are held at a warm temperature for long periods of time.

cat scratch disease

an infection connected with being clawed or bitten by a cat This disease is one of a group of diseases caused by different species of the small, gram-negative rod Bartonella henselae

endocarditis

an inflammation of the endocardium, or inner lining of the heart. Most of the time it refers to an infection of the valves of the heart, often the mitral or aortic valves Two variations of infectious endocarditis have been described: acute and subacute. Each has distinct groups of possible causative agents, most of which are bacterial organisms Symptoms include fever, anemia, abnormal heartbeat, and sometimes symptoms similar to myocardial infarction. Shortness of breath is a common symptom; additionally, chills may develop. Abdominal or side pain is sometimes reported. The patient may look very ill and may have petechiae (small, red-to-purple spots) over the upper half of the body and under the fingernails. Red, painless skin spots on the palms and the soles (Janeway lesions) and small, painful nodes on the pads of fingers and toes (Osler's nodes) may also be apparent on examination.

meningitis

an inflammation of the meninges an excellent example of an anatomical syndrome more serious forms are caused by bacteria, but it is thought that their entrance to the CNS is often facilitated by coinfection or previous infection with respiratory viruses No matter the cause, it results in these typical symptoms: photophobia (sensitivity to light), headache, painful or stiff neck, fever, and usually an increased number of white blood cells in the CSF. Many patients have described the headache associated with this disease as the "worst headache I have ever had."

pharyngitis

an inflammation of the throat, which the host experiences as pain and swelling. The severity of pain can range from moderate to severe, depending on the causative agent. Viral sore throats are generally mild and sometimes lead to hoarseness. Sore throats caused by bacteria are generally more painful than those caused by viruses, and they are more likely to be accompanied by fever, headache, and nausea. Clinical signs of a sore throat are reddened mucosa, swollen tonsils, and sometimes white packets of inflammatory products visible on the walls of the throat, especially in streptococcal disease. The mucous membranes may be swollen, affecting speech and swallowing. Often results in foul-smelling breath. The incubation period for most sore throats is generally 2 to 5 days. most serious cases are caused by Streptococcus pyogenes. Specialized polysaccharides on the surface of the cell wall help to protect the bacterium from being dissolved by the lysozyme of the host. Lipoteichoic acid (LTA) contributes to the adherence of S. pyogenes to epithelial cells in the pharynx. A spiky surface Page 621projection called M protein contributes to virulence by resisting phagocytosis and possibly by contributing to adherence. A capsule made of hyaluronic acid (HA) is formed by most S. pyogenes strains. It probably contributes to the bacterium's adhesiveness. Group A streptococci owe some of their virulence to the effects of hemolysins called streptolysins. The two types are streptolysin O (SLO) and streptolysin S (SLS).1 Both types cause beta-hemolysis of sheep blood agar. Both hemolysins rapidly injure many cells and tissues, including leukocytes and liver and heart muscle.

mumps

caused by an enveloped, single-stranded RNA virus (mumps virus) from the genus Paramyxovirus After an average incubation period of 2 to 3 weeks, symptoms of fever, nasal discharge, muscle pain, and malaise develop. These may be followed by inflammation of the salivary glands (especially the parotids), producing the classic gopherlike swelling of the cheeks on one or both sides. Swelling of the gland is called parotitis, and it can cause considerable discomfort. Viral multiplication in salivary glands is followed by invasion of other organs, especially the testes, ovaries, thyroid gland, pancreas, meninges, heart, and kidney. Despite the invasion of multiple organs, the prognosis of most infections is complete, uncomplicated recovery with permanent immunity. Diagnosis is usually based on ELISA tests for IgM or PCR on cheek swab. Negative results can be overruled if clinical signs are suggestive.

Botulism

an intoxication (that is, caused by an exotoxin) associated with eating poorly preserved foods, although it can also occur as a true infection. Clostridium botulinum, like Clostridium tetani, is an endospore-forming anaerobe that does its damage through the release of an exotoxin. Until recent times, it was relatively common and frequently fatal, but modern techniques of food preservation and medical treatment have reduced both its incidence and its fatality rate. a common cause of death in livestock that have grazed on contaminated food and in aquatic birds that have eaten decayed vegetation. There are three major forms, distinguished by their means of transmission and the population they affect. These are food-borne (in children and adults), infant, and wound. Food-borne in children and adults is an intoxication resulting from the ingestion of preformed toxin; the other two types are infections that are followed by the entrance of an exotoxin called botulinum toxin The effect of botulinum is to prevent the release of acetylcholine, the neurotransmitter that initiates the signal for muscle contraction. The usual time before onset of symptoms is 12 to 72 hours, depending on the size of the dose. Neuromuscular symptoms first affect the muscles of the head and include double vision, difficulty in swallowing, and dizziness, but there is no sensory or mental lapse. Later symptoms are descending muscular paralysis and respiratory compromise. In the past, death resulted from respiratory arrest, but mechanical respirators have reduced the fatality rate to about 10%. Several factors in food processing can lead to this. Endospores are present on the vegetables or meat at the time of gathering and are difficult to remove completely. When contaminated food is put in jars and steamed in a pressure cooker that does not reach reliable pressure and temperature, some endospores survive. At the same time, the pressure is sufficient to evacuate the air and create anaerobic conditions. Storage of the jars at room temperature favors endospore germination and vegetative growth, and one of the products of the cell's metabolism is botulinum, the most potent microbial toxin known.

acute Otitis Media (Ear Infection)

another common sequela of the common cold—for reasons similar to the ones described for sinusitis. Viral infections of the upper respiratory tract lead to inflammation of the eustachian tubes and the buildup of fluid in the middle ear, which can lead to bacterial multiplication in those fluids. Bacteria can migrate along the eustachian tube from the upper respiratory tract. When bacteria encounter mucus and fluid buildup in the middle ear, they multiply rapidly. Their presence increases the inflammatory response, leading to pus production and continued fluid secretion. This fluid is referred to as effusion. accompanied by a sensation of fullness or pain in the ear and loss of hearing. Younger children may exhibit irritability, fussiness, and difficulty in sleeping, eating, or hearing. Severe or untreated infections can lead to rupture of the eardrum because of pressure of pus buildup, or to internal breakthrough of these infected fluids, which can lead to more serious conditions such as mastoiditis, meningitis, or intracranial abscess. most common cause is Streptococcus pneumoniae a sequela of upper respiratory tract infection and is not communicable, although the upper respiratory infection preceding it is. Children are particularly susceptible, and boys have a slightly higher incidence than do girls.

influenza

begins in the upper respiratory tract but in serious cases may also affect the lower respiratory tract. There is a 1- to 4-day incubation period, after which symptoms begin very quickly. These include headache, chills, dry cough, body aches, fever, stuffy nose, and sore throat. can leave patients vulnerable to secondary infections, often bacterial. Influenza infection often leads to a pneumonia that can cause rapid death, even in young, healthy adults. Patients with emphysema or cardiopulmonary disease, along with very young, elderly, or pregnant patients, are more susceptible to serious complications. All cases are caused by one of three influenza viruses: A, B, or C. They belong to the family Orthomyxoviridae binds primarily to ciliated cells of the respiratory mucosa Inhalation of virus-laden aerosols and droplets constitutes the major route of influenza infection, although fomites can play a secondary role. Transmission is greatly facilitated by crowding and poor ventilation in classrooms, barracks, nursing homes, dormitories, and military installations in the late fall and winter.

Lyme disease

caused by Borrelia burgdorferi slow-acting, but it often evolves into a progressive syndrome that mimics neuromuscular and rheumatoid conditions. An early symptom in 70% of cases is a rash at the site of a tick bite. The lesion, called erythema migrans, can look like a bull's-eye, with a raised, erythematous (reddish) ring that gradually spreads outward and a pale central region Other early symptoms are fever, headache, stiff neck, and dizziness. If not treated or if treated too late, the disease can advance to the second stage, during which cardiac and neurological symptoms, such as facial palsy, can develop. After several weeks or months, a crippling polyarthritis can attack joints. Some people acquire chronic neurological complications that are severely disabling. Culture of the organism is not useful. Diagnosis in the early stages, while the rash is present, is usually accomplished based on symptoms and a history of possible exposure to ticks, since the organism is not easily detectable at this stage. ELISAs and/or Western blots can be used to detect antibodies to the organism in blood.

dengue fever

caused by one of four related single-stranded RNA flaviviruses carried by Aedes mosquitoes. also called "breakbone fever" because of the severe pain it can induce in muscles and joints (it does not actually cause fractures). The illness is endemic to Southeast Asia and India, and several epidemics have occurred in South America and Central America, the Caribbean, and Mexico. Although it typically presents as a mild infection, a new form of disease called dengue hemorrhagic fever (DHF) has emerged that causes high rates of morbidity and mortality in endemic areas. Dengue shock syndrome (DSS) can develop in DHF patients exhibiting life-threatening hypotension. Both forms of disease represent a major public health concern, as global warming has increased the geographic distribution of both the viruses and their vector to put nearly 3 billion people at risk for transmission of infection.

Infectious Mononucleosis

caused by the Epstein-Barr virus (EBV), a member of the family Herpesviridae The symptoms are sore throat, high fever, and cervical lymphadenopathy, which develop after a long incubation period (30 to 50 days). Many patients also have a gray-white exudate in the throat, a skin rash, and enlarged spleen and liver. A notable sign is sudden leukocytosis, consisting initially of infected B cells and later T cells. Fatigue is a hallmark of the disease. infection during the teen years results in disease about 25% of the time, whereas infection before or after this period is usually asymptomatic Direct oral contact and contamination with saliva are the principal modes of transmission, although transfer through blood transfusions, sexual contact, and organ transplants is possible. A differential blood count that shows excess lymphocytes, reduced neutrophils, and large, atypical lymphocytes with lobulated nuclei and vacuolated cytoplasm is suggestive of EBV infection (figure 20.11). A test called the "Monospot test" detects heterophile antibodies—which are antibodies that are not directed against EBV but are seen when a person has an EBV infection

salmonella

causes acute diarrhea (with or without vomiting) These bacteria are normal intestinal biota in cattle, poultry, rodents, and reptiles, and each (including domesticated pets) has been documented as a source of infection in humans. Animal products such as meat and milk can be readily contaminated during slaughter, collection, and processing. Inherent risks are involved in eating poorly cooked chicken or unpasteurized fresh or dried milk, ice cream, and cheese. The only prevention for salmonellosis is avoiding contact with the bacterium

Clostridium difficile

causes acute diarrhea (with or without vomiting) a gram-positive, endospore-forming rod found as normal biota in the intestine. It was once considered relatively harmless but now is known to cause a condition called pseudomembranous colitis, also known as antibiotic-associated colitis. In many cases, this infection is precipitated by therapy with broad-spectrum antibiotics. It is a major cause of diarrhea in hospitals, although community-acquired infections have been on the rise in the last few years. it is able to superinfect the large intestine when drugs have disrupted the normal biota. It produces two enterotoxins, toxins A and B, that cause areas of necrosis in the wall of the intestine. The predominant symptom is diarrhea. More severe cases exhibit abdominal cramps, fever, and leukocytosis. The colon is inflamed and gradually sloughs off loose, membranelike patches called pseudomembranes consisting of fibrin and cells. If the condition is not stopped, perforation of the cecum and death can result.

Rotavirus

causes acute diarrhea (with or without vomiting) a member of the Reovirus group, which consists of an unusual double-stranded RNA genome with both an inner and an outer capsid. Diagnosis is not always performed, as it is treated symptomatically. Stool samples from infected persons contain large amounts of virus, which is readily visible using electron microscopy The virus gets its name from its physical appearance, which is said to resemble a "spoked wheel." A rapid antigen test for stool specimens is commonly used in clinical settings, and an ELISA test is available. transmitted by the fecal-oral route, including through contaminated food, water, and fomites. For this reason, disease is most prevalent in areas of the world with poor sanitation The effects of infection vary with the age, nutritional state, general health, and living conditions of the patient. Babies from 6 to 24 months of age lacking maternal antibodies have the greatest risk for fatal disease. These children present symptoms of watery diarrhea, fever, vomiting, dehydration, and shock. The intestinal mucosa can be damaged in a way that chronically compromises nutrition, and long-term or repeated infections can retard growth. Newborns seem to be protected by maternal antibodies. Adults can also acquire this infection, but it is generally mild and self-limiting. Children are treated with oral replacement fluid and electrolytes

Cryptosporidium

causes acute diarrhea (with or without vomiting) an intestinal protozoan of the apicomplexan type that infects a variety of mammals, birds, and reptiles The organism's life cycle includes a hardy intestinal oocyst as well as a tissue phase. Humans accidentally ingest the oocysts with water or food that has been contaminated by feces from infected animals. The oocyst "excysts" once it reaches the intestines and releases sporozoites that attach to the epithelium of the small intestine The organism penetrates the intestinal cells and lives intracellularly within them. It undergoes asexual and sexual reproduction in these cells and produces more oocysts, which are released into the gut lumen, excreted from the host, and after a short time become infective again. The oocysts are highly infectious and extremely resistant to treatment with chlorine and other disinfectants. The prominent symptoms mimic other types of gastroenteritis, with headache, sweating, vomiting, severe abdominal cramps, and diarrhea. AIDS patients may experience chronic, persistent cryptosporidial diarrhea that can be used as a criterion to help diagnose AIDS

vibrio cholerae

causes acute diarrhea (with or without vomiting) comma-shaped rods with a single polar flagellum. They belong to the family Vibrionaceae. A freshly isolated specimen contains quick, darting cells that slightly resemble a comma After an incubation period of a few hours to a few days, symptoms begin abruptly with vomiting, followed by copious watery feces called secretory diarrhea. The intestinal contents are lost very quickly, leaving only secreted fluids. This voided fluid contains flecks of mucus—hence, the description "rice-water stool." Fluid losses of nearly 1 liter per hour have been reported in severe cases, and an untreated patient can lose up to 50% of body weight during the course of this disease. The diarrhea causes loss of blood volume, acidosis from bicarbonate loss, and potassium depletion, which manifest in muscle cramps, severe thirst, flaccid skin, sunken eyes, and—in young children—coma and convulsions. Secondary circulatory consequences can include hypotension, tachycardia, cyanosis, and collapse from shock within 18 to 24 hours. The virulence of V. cholerae lies mainly in the action of an enterotoxin called cholera toxin (CT), which disrupts the normal physiology of intestinal cells. When this toxin binds to specific intestinal receptors, a secondary signaling system is activated. Under the influence of this system, the cells shed large amounts of electrolytes into the intestine, an event accompanied by profuse water loss. It was recently discovered that V. cholerae uses quorum sensing to regulate the precise expression of its virulence factors, making proteins used in this process potential targets for drug therapy. can be readily isolated and identified in the laboratory from stool samples. Direct dark-field microscopic observation reveals characteristic curved cells with brisk, darting motility as confirmatory evidence. Effective prevention is contingent on proper sewage treatment and water purification.

campylobacter

causes acute diarrhea (with or without vomiting) slender, curved or spiral, gram-negative bacteria propelled by polar flagella at one or both poles, often appearing in S-shaped or gull-winged pairs causes more diarrhea than Salmonella and Shigella combined Campylobacter jejuni is the most common cause of diarrhea, although there are other pathogenic species. tend to be microaerophilic inhabitants of the intestinal tract, genitourinary tract, and oral cavity of humans and animals Transmission of this pathogen takes place via the ingestion of contaminated beverages and food, especially water, milk, meat, and chicken. Recent studies suggest that C. jejuni is much more resistant to heating temperatures during the cooking process than was previously estimated, increasing the need for proper food handling. The single most common precipitating event for the onset of Guillain-Barré syndrome

STEC (Shiga-Toxin-Producing E. coli)

causes acute diarrhea (with or without vomiting) the agent of a spectrum of conditions, ranging from mild gastroenteritis with fever to bloody diarrhea. About 10% of patients develop hemolytic uremic syndrome (HUS), a severe hemolytic anemia that can cause kidney damage and failure. Neurological symptoms such as blindness, seizure, and stroke (and long-term debilitation) are also possible. These serious manifestations are most likely to occur in children younger than age 5 and in elderly people. efface (rub out or destroy) enterocytes, which are gut epithelial cells. The net effect is a lesion in the gut (effacement), usually in the large intestine. The microvilli are lost from the gut epithelium, and the lesions produce bloody diarrhea. The most common mode of transmission is the ingestion of contaminated and undercooked beef, although other foods and beverages can be contaminated as well. Ground beef is more dangerous than steaks or other cuts of meat Other farm products may also become contaminated by cattle feces. Products that are eaten raw, such as lettuce, vegetables, and apples used in unpasteurized cider, are particularly problematic. The best prevention for this disease is to never eat raw or even rare hamburger and to wash raw vegetables well. The shiga toxin is heat-labile, and the E. coli is killed by heat

norovirus

causes acute diarrhea (with or without vomiting) the most common cause of food-borne illness in the United States. Transmission is fecal-oral or via contamination of food and water. Viruses generally cause a profuse, watery diarrhea of 3 to 5 days duration. Severe vomiting is a feature of the disease, especially in the early phases. Mild fever is often seen Treatment of these infections always focuses on rehydration

shigella

causes acute diarrhea (with or without vomiting) these bacteria are gram-negative, straight rods, nonmotile and non-endospore-forming. They do not produce urease or hydrogen sulfide, traits that help in their identification. They are primarily human parasites, though they can infect apes Although Shigella dysenteriae causes the most severe form of dysentery, it is uncommon in the United States and occurs primarily in the Eastern Hemisphere. -- produces a heat-labile exotoxin called *shiga toxin*, which seems to be responsible for the more serious damage to the intestine as well as any systemic effects, including injury to nerve cell In the past decade, the prevalent agents in the United States have been Shigella sonnei and Shigella flexneri, which cause approximately 20,000 to 25,000 cases each year, half of them in children. frequent, watery stools; fever; and often intense abdominal pain. Nausea and vomiting are common. Stools often contain obvious blood and even more often are found to have occult (not visible to the naked eye) blood. Diarrhea containing blood is also called dysentery. Mucus from the GI tract will also be present in the stools. invades the villus cells of the large intestine rather than the small intestine. In addition, it is not as invasive as Salmonella and does not perforate the intestine or invade the blood. It enters the intestinal mucosa by means of lymphoid cells in Peyer's patches. Once in the mucosa, Shigella instigates an inflammatory response that causes extensive tissue destruction. The release of endotoxin causes fever also acquired through direct person-to-person contact, largely because of the small infectious dose required

chronic diarrhea

diarrhea lasting longer than 14 days. It can have infectious causes or can reflect noninfectious conditions. Most of us are familiar with diseases that present a constellation of bowel syndromes, such as irritable bowel syndrome and ulcerative colitis. When the presence of an infectious agent is ruled out by a negative stool culture or other tests, these conditions are suspected. People suffering from AIDS almost universally suffer from this

Enteroaggregative E. coli (EAEC)

distinguished by its ability to adhere to human cells in aggregates rather than as single cells Its presence appears to stimulate secretion of large amounts of mucus in the gut, which may be part of its role in causing chronic diarrhea. The bacterium also seems capable of exerting toxic effects on the gut epithelium, although the mechanisms are not well understood. Transmission of the bacterium is through contaminated food and water.

respiratory syncytial virus

infects the respiratory tract and produces giant, multinucleated cells (syncytia). It is a member of the paramyxovirus family and contains single-stranded, negative-sense RNA. It is an enveloped virus. Children 6 months of age or younger, as well as premature babies, are especially susceptible to serious disease caused by this virus. RSV is the most prevalent cause of respiratory infection in the newborn age group, and nearly all children have experienced it by age 2. An estimated 100,000 children are hospitalized with RSV disease each year in the United States. The mortality rate is highest for children with complications such as prematurity, congenital disease, and immunodeficiency. Infection in older children and adults usually manifests as a cold. The first symptoms are fever that lasts for approximately 3 days, rhinitis, pharyngitis, and otitis. More serious infections progress to the bronchial tree and lung parenchyma, giving rise to symptoms of croup, which include acute bouts of coughing, wheezing, dyspnea, and rales. This condition is often called "croup" and bronchiolitis; be aware that both of these terms are clinical descriptions of diseases caused by a variety of viruses (in addition to RSV) and sometimes bacteria. The virus is highly contagious and is transmitted through droplet contact but also through fomite contamination. There is no RSV vaccine available yet, but an effective passive antibody preparation (Synagis) is used as prevention in high-risk children and babies born prematurely

cold

often called rhinitis, from the Latin word rhin, meaning "nose," and the suffix -itis, meaning "inflammation." sneezing, scratchy throat, and runny nose (rhinorrhea) usually begin 2 or 3 days after infection. Generally is not accompanied by fever, although children can experience low fevers (less than 102°F). Note that people with asthma and other underlying respiratory conditions (COPD) often suffer more severe symptoms triggered by this. caused by one of over 200 different kinds of viruses. The particular virus is almost never identified, and the symptoms and handling of the infection are the same no matter which of the viruses is responsible. most common type of virus leading to this is the group called rhinoviruses, of which there are 99 serotypes. Coronaviruses and adenoviruses are also major causes. Most viruses causing this never lead to any serious consequences, but some of them can be serious for some patients. The respiratory syncytial virus (RSV) causes colds in most people, but in some, especially infants, infection with this virus can lead to more serious respiratory tract symptoms do not have many virulence mechanisms transmitted by droplet contact, but indirect transmission may be more common, such as when a healthy person touches a fomite and then touches one of his or her own vulnerable surfaces, such as the mouth, nose, or an eye. In some cases, the viruses can remain airborne in droplet nuclei and aerosols and can be transmitted via the respiratory route. A wide variety of over-the-counter agents, such as antihistamines and decongestants, improve symptoms by blocking inflammatory mediators and their action

streptococcus pneumoniae

organism that accounts for about 40% of community-acquired pneumonia cases. often simply called the pneumococcus, is a small, gram-positive, flattened coccus that often appears in pairs, lined up end to end. It is alpha-hemolytic on blood agar Infection can occur when the bacterium is inhaled into deep areas of the lung or by transfer of the bacterium between two people via respiratory droplets The polysaccharide capsule of the bacterium prevents efficient phagocytosis, apparently by blocking the attachment of complement, with the result that the fluids of inflammation are continuously released into the lungs. As the infection and inflammation spread rapidly through the lung, the patient can actually "drown" in his or her own secretions. If this mixture of exudates, cells, and bacteria solidifies in the air spaces, a condition known as consolidation occurs. Systemic complications of pneumonia are pleuritis and endocarditis, but pneumococcal bacteremia and meningitis are the greatest danger to the patient resistant to penicillin and its derivatives, as well as to the macrolides, tetracyclines, and fluoroquinolones; therefore, broad-spectrum cephalosporins are now typically prescribed for drug therapy, with or without vancomycin.

Neisseria meningitidis

organism that appears as gram-negative diplococci lined up side by side in microscopic analysis (figure 19.3) and is commonly known as the meningococcus often associated with epidemic forms of meningitis. This organism causes the most serious form of acute meningitis, and it is responsible for about 25% of all meningitis cases. Most cases occur in young children, since vaccination of otherwise healthy children against this disease is not recommended until age 11 The portal of entry for this pathogen is the upper respiratory tract. The bacterium passes into surrounding blood vessels, rapidly penetrating the meninges and producing symptoms of meningitis. The most serious complications of meningococcal infection are due to meningococcemia, which can accompany meningitis but can also occur on its own. The pathogen releases endotoxin within the bloodstream, which acts as a potent white blood cell stimulator. The pathogen has a natural ability to avoid destruction through its production of IgA protease and the presence of a capsule. The scene is set for transmission when carriers live in close quarters with nonimmune individuals, as may be expected in families, day care facilities, college dormitories, and military barracks Treatment is usually begun with this bacterium in mind until it can be ruled out. Cerebrospinal fluid, blood, or nasopharyngeal samples are stained and observed directly for the characteristic gram-negative diplococci. Cultivation may be necessary to differentiate the bacterium from other species. Specific rapid tests are also available for detecting the capsular polysaccharide or the cells directly from specimens without culturing.

Streptococcus pneumoniae

organism that causes the majority of bacterial pneumonias. (It is also referred to as the pneumococcus.) this pathogen is the most frequent cause of community-acquired meningitis and often causes a severe form of the disease. It does not cause the petechiae associated with meningococcal meningitis, and that difference is useful diagnostically. Pneumococcal meningitis is most likely to occur in patients with underlying susceptibility, such as patients with alcoholism, patients with sickle-cell disease, and those with absent or defective spleen function. Up to 25% of pneumococcal meningitis patients will also develop pneumococcal pneumonia. produces an alpha-hemolysin (observable on blood agar) and hydrogen peroxide, both of which have been shown to induce damage in the CNS, such as inducing brain cell apoptosis.

chagas disease

sometimes called "the American trypanosomiasis." The causative agent is Trypanosoma cruzi. it can cloak itself in host proteins, disguising itself from the immune system. It can also induce autoimmunity, so that the same immune cells trained to recognize it begin to react with host tissues, causing the symptoms of late-stage Chagas disease. Once the trypanosomes are transmitted by a group of insects called the triatomines, they multiply in muscle and blood cells The disease manifestations are divided into acute and chronic phases. Soon after infection, the acute phase begins; symptoms are relatively nondescript and range from mild to severe fever, nausea, and fatigue. A swelling called a "chagoma" at the site of the bug bite may be present. If the bug bite is close to the eyes, a distinct condition called Romana's sign, swelling of the eyelids, may appear. The acute phase lasts for weeks or months after which the condition becomes chronic and virtually asymptomatic for a period of years or indefinitely. Eventually, the trypanosomes are found in numerous sites around the body, which in later years may lead to inflammation and disruption of function in organs such as the heart, the brain, and the intestinal tract.

hepatitis C

sometimes referred to as the "silent epidemic" because 3.5 million Americans are infected with the virus, but it takes many years to cause noticeable symptoms. Liver failure from this is one of the most common reasons for liver transplants in this country. an RNA virus in the Flaviviridae family much more likely to become chronic The virus's core protein seems to play a role in the suppression of cell-mediated immunity as well as in the production of various cytokines. The protein may also be responsible for altering mitochondrial activity in HCV-infected cells It is more commonly transmitted through blood contact (both "sanctioned," such as in blood transfusions, and "unsanctioned," such as needle sharing by injecting drug users) than through transfer of other body fluids. Vertical transmission is also possible.

aseptic meningitis

the majority of cases occur in children, and 90% are caused by enteroviruses. But many other viruses also gain access to the central nervous system on occasion. An initial infection with herpes simplex type 2 is sometimes known to cause meningitis; other herpesviruses, such as HHV-6, HHV-7, and HHV-3 (the chickenpox virus), can infect the meninges as well. Arboviruses, arenaviruses, and adenoviruses have also been identified as causative agents of meningitis; and it is recognized that HIV infection may manifest as meningitis even when the virus is controlled in the rest of the body. Viral meningitis is generally milder than bacterial or fungal meningitis, and it is usually resolved within 2 weeks. The mortality rate is less than 1%. Diagnosis begins with the failure to find bacteria, fungi, or protozoa in CSF and can be confirmed, depending on the virus, by viral culture or specific antigen tests. In most cases, no treatment is indicated. Acyclovir can be used when the causative agent is a herpesvirus; of course, if HIV is involved, the entire HIV antiviral regimen is merited

dental caries (tooth decay)

the most common infectious disease of human beings. The process involves the dissolution of solid tooth surface due to the metabolic action of bacteria. The symptoms are often not noticeable but range from minor disruption in the outer (enamel) surface of the tooth to complete destruction of the enamel and then destruction of deeper layers Deeper lesions can result in infection to the soft tissue inside the tooth, called the pulp, which contains blood vessels and nerves. These deeper infections lead to pain, referred to as a "toothache." Two representatives of oral alpha-hemolytic streptococci, *Streptococcus mutans* and *Streptococcus sobrinus*, seem to be the main causes A specific condition called early childhood caries may also be caused by a newly identified species, *Scardovia wiggsiae*. Note that in the absence of dietary carbohydrates, bacteria do not cause decay. Teeth become vulnerable to caries as soon as they appear in the mouth at around 6 months of age. transmitted to babies and children by their close contacts, especially the mother or closest caregiver. There is evidence for transfer of oral bacteria between children in day care centers as well. Although it was previously believed that humans do not acquire S. mutans or S. sobrinus until the eruption of teeth in the mouth, it now seems likely that both of these species may survive in the infant's oral cavity prior to appearance of the first teeth.

scarlet fever

the result of infection with an S. pyogenes strain that is itself infected with a bacteriophage. This lysogenic virus confers on the streptococcus the ability to produce erythrogenic toxin, described in the section on virulence. characterized by a sandpaper-like rash, most often on the neck, chest, elbows, and inner surfaces of the thighs. High fever accompanies the rash. It most often affects school-age children and was a source of great suffering in the United States in the early part of the 20th century. In epidemic form, the disease can have a fatality rate of up to 95%. Most cases seen today are mild. They are easily recognizable and amenable to antibiotic therapy. Because of the fear elicited by the name "scarlet fever," the disease is often called "scarlatina" in North America. A key toxin in the development of scarlet fever is erythrogenic toxin. This toxin is responsible for the bright red rash typical of this disease, and it induces fever by acting upon the temperature regulatory center in the brain.

Eastern Equine Encephalitis (EEE)

this arbovirus is endemic to an area along the eastern coast of North America and Canada. The usual pattern is sporadic, but epidemics can occur in humans and horses. Its life cycle involves birds and mosquitoes. Cases of disease usually appear first in horses and caged birds; a vaccine exists for horses, and its use is strongly urged to eliminate the virus from this reservoir. In humans, the case fatality rate can be very high (70%).

Powassan Virus

this arbovirus is maintained in nature by ticks and groundhogs. In 2013, it caused 15 (reported) cases of encephalitis. Its geographic distribution is in the Northeast and the Great Lakes states.

Toxoplasma gondii

this organism is a flagellated parasite (obligate intracellular parasite) with such extensive distribution that some experts estimate it affects the majority of the world's population at some time in their lives. Infection in the fetus and in immunodeficient people, especially those with AIDS, is severe and often fatal. Although infection in otherwise healthy people is generally unnoticed, recent data tells us it can have profound effects on their brain and the responses it controls It seems that people with a history of this infection are more likely to display thrill-seeking behaviors and other significant changes in their brains. most cases are asymptomatic or marked by mild symptoms such as sore throat, lymph node enlargement, and low-grade fever. In patients whose immunity is suppressed by infection, cancer, or drugs, the outlook may be grim. The infection causes a more chronic or subacute form of encephalitis than do most viruses, often producing extensive brain lesions and fatal disruptions of the heart and lungs. A pregnant woman with this has a 33% chance of transmitting the infection to her fetus. Congenital infection occurring in the first or second trimester is associated with stillbirth and severe abnormalities such as liver and spleen enlargement, liver failure, hydrocephalus, convulsions, and damage to the retina that can result in blindness.

Herpes Simplex Virus

this virus can cause encephalitis in newborns born to HSV-positive mothers. In this case, the virus is disseminated and the prognosis is poor. Older children and young adults (ages 5 to 30), as well as older adults (over 50 years old), are also susceptible to herpes simplex encephalitis, caused most commonly by HSV-I. In these cases, the HSV encephalitis usually represents a reactivation of dormant HSV from the trigeminal ganglion.

JC virus

this virus gets its name from the initials of the patient in whom it was first diagnosed as the cause of illness. Seroprevalence of this polyomavirus nears 80% in many parts of the United States and Europe, though most infections are asymptomatic. In patients with immune dysfunction, especially in those with AIDS, this pathogen can cause a condition called progressive multifocal leukoencephalopathy. This uncommon but generally fatal infection is a result of virus attack of accessory brain cells. The infection demyelinizes certain parts of the cerebrum. This virus should be considered when encephalitis symptoms are observed in AIDS patients

rheumatic fever

thought to be due to an immunologic cross-reaction between the streptococcal M protein and heart muscle. It tends to occur approximately 3 weeks after pharyngitis has subsided. It can result in permanent damage to heart valves. Other symptoms include arthritis in multiple joints and the appearance of nodules over bony surfaces just under the skin.

Glomerulonephritis

thought to be the result of streptococcal proteins participating in the formation of antigen-antibody complexes, which then are deposited in the basement membrane of the glomeruli of the kidney. It is characterized by nephritis (appearing as swelling in the hands and feet and low urine output), blood in the urine, increased blood pressure, and occasionally heart failure. It can result in permanent kidney damage. The incidence of poststreptococcal glomerulonephritis has been declining in the United States, but it is still common in Africa, the Caribbean, and South America.

acute diarrhea (with or without vomiting)

three or more loose stools in a 24-hour period transmitted by contaminated food (contaminated hamburgers or Salmonella-contaminated ice cream.)