ch.13.5-16&17.3 Micro

Meningitis Signs and Symptoms

(Typical symptoms, regardless of causative agent) • Headache, painful or stiff neck • Fever, nausea and vomiting; skin rash in some cases • Photophobia (sensitivity to light) • Increased number of lymphocytes in the CSF

Streptococcus (Phylum Firmicutes; Gram +)

- Aerotolerant anaerobe ("lactic acid bacteria") - Homofermentative - lactic acid as sole product - Genus includes the pathogens S. pneumoniae, S. pyogenes

Staphylococcus (Phylum Firmicutes; Gram +)

- Facultative anaerobe (fermentation) - Commensals (S. epidermidis) and pathogens (S. aureus)

Propionibacterium (Phylum Actinobacteria; Gram +)

- Facultative or aerotolerant anaerobes - Live in follicles, pores; ferment sebum, acids, carbs - P. acens is implicated in acne

Corynebacterium (Actinobacteria)

- Obligately aerobic or facultatively anaerobic - Includes the pathogen C. diphtheriae, cause of diptheria

Signs and symptoms specific to meningococcemia

- Sudden onset of disease - Fever higher than 40°C or 104°F, chills, delirium, sore throat - Widespread bleeding under the skin - Generalized intravascular clotting - Shock, coma, cardiac failure - Death within a few hours

Stratum basale

Attached to the dermis, source of epidermis cells

Defenses of the skin "Shedding" as a mechanical defense:

Millions of cells of the stratum corneumslough off daily, taking microorganisms with them

Prions: CJD

No current treatment or vaccine exists

Keratin

Protein that give cells the ability to withstand damage, abrasion, and water penetration

Natural immunity

any immunity that is acquired through the normal biological experiences of an individual

Lysozyme

enzyme found in sweat, tears, saliva • Breaks down peptidoglycan in bacterial cell walls

Maculopapular rash diseases

flat to slightly raised colored bumps • Measles • Rubella • Fifth disease • Roseola • Scarlet fever

Vesicular or Pustular Rash Diseases

• Chickenpox: very common and mostly benign • Small pox: even a single case constitutes a public health emergency • Both present as generalized rashes • Pox: individual lesions that contain fluid

Aseptic meningitis

no bacteria or fungi are found in the CSF • Usually these are cases of viral meningitis • Majority of cases occur in children • 90% caused by enteroviruses (a type of single-stranded RNA viruses) • Other viruses can gain access to the CNS as well • Generally milder than bacterial or fungal meningitis • Usually resolved within 2 weeks • Mortality rate less than 1% • Diagnosis begins with the failure to find bacteria, fungi, or protozoa in the CSF • Confirmed by viral culture or specific antigen tests • In most cases, no treatment is needed

Measles Culture and Diagnosis

• Clinical presentation, ELISA to test for IgM to measles antigen

Impetigo: S. aureus Pathogenesis and Virulence Factors • Coagulase

• Coagulates plasma • Helps pathogen evade immune system • 97% of all human isolates produce this enzyme; considered diagnostic of the species

Artificial immunity

protection from infection obtained through medical procedures such as vaccines and immune serum

conjugated vaccines

subunits conjugated with proteins to make them more immunogenic

Stratum corneum

~25 cells thick, dead cells that have migrated from the deeper layers, constantly at the surface

Meningitis: Listeria monocytogenes Culture and Diagnosis

• Cold enrichment used to isolate the organism • Specimen is held at 4°C and periodically plated onto media • Procedure can take 4 weeks • Rapid diagnostic kits using ELISA (detection by antibodies) and other techniques are available for direct testing of dairy products (faster!)

Prions • Proteinaceous infectious particles

• Contain no genetic material • Basically, these are normal proteins that have "misfolded" in a special way, and that can cause similar proteins to misfold

Impetigo Signs and Symptoms

• "Lesion" looks like peeling skin, crusty and flaky scabs, or honey-colored crusts • most often found around the mouth, face, and extremities, but can occur anywhere on the skin • symptomatology does not indicate whether the infection is caused by Staphylococcus or Streptococcus

Measles (also known as rubeola)

• >500 children die every day from measles, even though an effective vaccine is available since • Since 2002, measles deaths have dropped 74% • In developed countries, many parents are opting not to vaccinate their children against measles due to unfounded fears that Autism is linked to the MMR vaccine

Smallpox

• After a comprehensive global effort by the World Health Organization, smallpox is largely a disease of the past • After the anthrax bioterrorism in 2001, the U.S. began taking the threat of smallpox bioterrorism seriously • Vaccination had been discontinued when the disease was eradicated, but is now offered to certain U.S. populations

Prions Signs and Symptoms

• Altered behavior, memory loss, impaired senses, delirium, senility • Muscle contractions and death, usually within a year of diagnosis

Meningitis: Listeria monocytogenes Prevention and Treatment

• Antibiotic therapy should be started as soon as listeriosis is suspected • Prevention can be improved by adequate pasteurization temperatures • Proper washing, refrigeration, and cooking of foods • Infectious dose is 10-100 million...just need to prevent exposure to large amounts, i.e. prevent growth • Pregnant women cautioned not to eat soft, unpasteurized cheeses

Rubella Prevention and Treatment

• Attenuated rubella virus vaccine in the combined form (MMR vaccination) • Given to children at 12 and 15 months, booster at 4 or 6 years of age • Vaccine for rubella can be given alone, without the measles or mumps component • Postnatal rubella is generally benign and requires symptomatic treatment • No specific treatment is available for congenital rubella

Meningitis Transmission and Epidemiology

• Bacteria do not survive long in the environment • Usually acquired through close contact with secretions or droplets • Reservoir is humans harboring the pathogen in the nasopharynx • Carriage state lasting a few days to several months, exists in 3 - 30% of the adult population; >50% in institutional settings • Carriers living in close quarters with susceptible individuals more readily transmit the disease • Families, day care facilities • college dormitories, military barracks • Highest risk groups are • 6 - 36 months old; 10 - 20 years old

Meningitis Pathogenesis and Virulence Factors

• Bacteria entering the blood vessels rapidly penetrate the meninges and produce symptoms • Pathogen releases endotoxin into the generalized circulation which stimulates white blood cells • Damage to the blood vessels caused by cytokines leads to vascular collapse, hemorrhage, and petechiae on the trunk and appendages • In a small number of cases, meningococcemia becomes an overwhelming disease with a high mortality rate • Bacterium produces IgA protease and a capsule that counter the body's defenses

Impetigo Caused by Streptococcus pyogenes • Gram-positive coccus

• Beta-hemolytic on blood agar • Also causes streptococcal pharyngitis, scarlet fever, pneumonia, puerperal fever, necrotizing fasciitis, serious bloodstream infections, and post stretpococcal infections such as rheumatic fever

Meningitis: Cryptococcus neoformans (Fungi) Signs and Symptoms

• Causes a chronic form of meningitis with a gradual onset of symptoms • Onset may be fast in AIDS patients and the disease more acute • Sometimes classified as meningoencephalitis • Headache most common symptom • nausea and neck stiffness also common

Prions: CJD Causative Agent: Prion

• Causes transformation of a normal host protein (PrP) that functions in normal brain development • Mutation causes a structural change in the protein, making PrP catalytic and able to convert other normal PrP proteins into the abnormal form • Abnormal PrP proteins start a self-propagating chain that creates a massive accumulation of altered PrP • plaques form in the brain, causing spongiform damage and severe loss of brain function • Prions are considered transmissible agents • PrP proteins can be acquired through transmission • genetic mutations of the PrP gene can also be passed on as heritable traits • Prions are hardy "pathogens" • resistant to chemicals, radiation, heat, and prolonged autoclaving

The Nervous System and Its Defenses Component parts of the immune system

• Central nervous system (CNS): consists of the brain and spinal cord • Peripheral nervous system (PNS): contains nerves that emanate from the CNS to sense organs and periphery of the body • Brain and spinal cord encased within three meninges • Dura mater (outermost layer), arachnoid mater, and pia mater • Space between the arachnoid and pia mater is filled with cerebrospinal fluid (CSF) • CSF provides nutrients and a "cushion" for CNS organs

Meningitis: Neisseria meningitidis Culture and Diagnosis (continued)

• Cerebrospinal fluid, blood, and nasopharyngeal samples are taken • Stained and observed for characteristic diplococci • Cultivation may be necessary to differentiate from other species • Modified Thayer-Martin or chocolate agar (lysed blood cells) are used • Provide a variety of complex nutrients required for Neisseria • Media is incubated at a high CO2(enhances growth) • Specific rapid tests are available for detecting capsular polysaccharide or cells directly from specimens without culturing • Presumptive identification of the genus obtained through • Gram stain (Gram negative diplococci) • Oxidase testing

Sweat

• Inhibitory to microorganisms due to low pH and high salt concentration

Measles Pathogenesis and Virulence Factors

• Course of infection • Virus implants on respiratory mucosa and infects the tracheal and bronchial cells • Travels to the lymphatic system where it multiplies and enters the bloodstream • Viremia carries the virus to the skin and various organs • Virus can evade cell-mediated immunity

Development of New Vaccines

• Dozens of bacterial, viral, protozoan, and fungal diseases remain without a functional vaccine • malaria, HIV/AIDS, diarrheal diseases, respiratory diseases, and worm infections that affect over 200 million people per year • In some cases vaccines exist but are not widely available • Difficult to design vaccines for latent or persistent viral infections • herpesviruses and cytomegaloviruses • since the host's natural immunity cannot clear the virus, the artificial immunity must outperform the host's natural response

Rubella Transmission and Epidemiology

• Endemic disease with worldwide distribution • Initiated through contact with respiratory secretions and occasionally urine • Virus is shed through prodromal phase and up to a week after the rash appears • Virus is only moderately communicable; close living conditions are required for its spread • Well controlled in the U.S.; fewer than 10 cases reported in each of the last several years

Impetigo Catalase test

• Enzyme breaks down hydrogen peroxide accumulated during oxidative metabolism • Used to differentiate the staphylococci from the streptococci

Impetigo Pathogenesis and Virulence Factors

• Exfoliative toxins A and B • Coded for by a phage that infects some strains of S. aureus • Attack a protein important in cell-to-cell binding in the epithelium • Leads to characteristic blistering • Breakdown of skin architecture facilitates spread of the bacterium • Possesses a huge arsenal of enzymes and toxins • S. pyogenes is more often the cause of impetigo in newborns; S. aureus is more often the cause of impetigo in older children • Both can cause infection in either age group

Dermis

• Fibroblast cells and collagen; harbors a dense network of nerves, blood vessels, and lymphatic vessels • damage that petrates the dermis results in broken blood vessels • Follicles: roots of hairs located in the dermis • Sebaceous (oil) glands: secrete sebum, associated with the hair follicles • Sweat glands also found in the dermis • Glands have openings on the surface that pass through the epidermis

Smallpox Prevention

• First successful vaccine produced by Edward Jenner in 1796, by exposure of patient to related but non-virulent cowpox • Vaccine now is another related virus, vaccinia virus (mild infection) • A massive vaccination effort from 1967-1977 eradicated the disease

Integument

• Forms the boundary between the human and the environment • Includes the skin, hair, nails, and sweat and oil glands • Major layers of the skin: Epidermis and dermis • Epidermis

Meningitis: Coccidioides species Causative Agent and epidemiology

• Fungi native to southwestern US • Forms white/brown colonies with abundant, branching, septate hyphae that fragment into thick-walled, block-like arthrospores • Athrospore germinates into a small, parasitic cell called a spherule • Two species: C. immitis is responsible for disease in California's San Joaquin valley and C. posadasil is more widely distributed in the U.S. southwest, Mexico, and South America • Outbreak after Northridge earthquake (1994) due to dispersal of airborne spores

Meningitis: Cryptococcus neoformans (Fungi) Causative Agent

• Fungus with a spherical or ovoid shape • Small, constricted buds • Large capsule

Measles Causative Agent

• Genus Morbillivirus, family Paramyxovirus • Enveloped, single-stranded RNA virus

Impetigo Prevention

• Good hygiene; Vaccines are in development, but none currently available

Meningitis: Listeria monocytogenes (Phylum Firmicutes) Causative agent: Listeria monocytogenes

• Gram positive, coccobacilli (short rods) • Facultative anaerobe • No capsule production, motile by flagella

Causative agents of meningitis Neisseria meningitidis (Phylum Proteobacteria)

• Gram-negative diplococcic (pairs) • Commonly known as the meningococcus • Often associated with epidemic forms of meningitis • Causes the most serious form of acute meningitis

Impetigo Caused by Staphylococcus aureus

• Gram-positive coccus that grows in clusters • Nonmotile • Produces a variety of superantigens • Considered to be the sturdiest of all non-spore-forming pathogens • Withstands high salt (7 - 10%), tolerates high temperatures • Remains viable after months of air drying • Resists the effects of disinfectants and antibiotics (e.g. MRSA)

Meningitis Pathogenesis and Virulence Factors

• Has a polysaccharide capsule that protects it against phagocytosis • Produces an alpha-hemolysin and hydrogen peroxide that produce damage in the CNS • Capable of inducing brain cell apoptosis • Can penetrate the respiratory mucosa, gain access to the bloodstream, and enter the meninge

Prions: CJD Transmission and Epidemiology

• In the late 1990s, humans contracted vCJD after ingesting meat from cattle that had been afflicted with BSE • Meat products had been contaminated with fluid or tissues infected with the prion • Cases were centered around Great Britain, where many cows were found to have BSE • Median age at death of patients with vCJD is 28 years • Median age at death of patients with other forms of CJD is 68 years • Health care professionals should be aware of the possibility of CJD in patients • Cases have been reported of transmission of CJD via contaminated surgical instruments • Normal disinfection and sterilization procedures are not sufficient to eliminate the agent from instruments and surfaces

Meningitis: Neisseria meningitidis Prevention and Treatment

• Infection rate in most populations is 1% indicating a well-developed natural immunity • Natural immunization occurs as one is exposed to the meningococcusand its relatives • Treated meningococcemial disease has a mortality rate of 15% • Vital that chemotherapy begin as soon as possible • High doses of penicillin G given intravenously • Treatment for shock and intravascular clotting may also be required • Individuals in close contact with infected patients should receive preventative therapy with rifampin or tetracycline • New vaccine developed in 2005 recommended for children at elevated risk

Normal biota of the nervous system...none known!

• It is still believed that there is no normal biota in either the CNS or PNS • finding microorganisms of any type in these tissues represents deviation from the healthy state • herpes viruses live in a dormant state in the nervous system, but are not considered normal microbiota

Impetigo Coagulase test

• Key technique that separates S. aureus from other species of Staphylococcus • Any isolate that coagulates plasma is • S. aureus; all others are coagulase negative • Aids in diagnosis

Measles Sequelae and Complications

• Laryngitis, pneumonia, secondary bacterial infections such as ear and sinus infections, additional complications; see • Death in many cases is due to secondary infections, e.g. pneumonia

Rubella

• Latin for "little red", also known as German measles • Relatively minor rash disease with few complications • Serious damage can occur to the fetus in utero • women of childbearing years must be sure to have been vaccinated before they plan to conceive

Sebum

• Low pH of sebum makes the skin inhospitable to microorganisms • Lipids in sebum serve as nutrients to microbiota • Toxic byproducts of fatty acid metabolism inhibit the growth of microorganisms not adapted to the skin environment

Measles Prevention

• MMR (mumps, measles, rubella) vaccine contains live, attenuated measles virus that confers protection for up to 20 years

Infectious Nervous System Diseases: Meningitis

• Meningitis is cause by inflammation of the meninges • Anatomical syndrome: many different microorganisms (bacteria, fungi, viruses) can cause an infection of the meninges and all cause the same constellation of symptoms • Inflammation is a results of growth of microbes in the CSF • More serious forms of acute meningitis are caused by bacteria • entrance to the CNS facilitated by coinfection or previous infection with respiratory viruses • Meningitis in neonates is most often caused by different microorganisms than those causing disease in children and adults • Lumbar puncture (spinal tap), Gram stain, and/or culture of CSF are performed when meningitis is suspected • Treatment with broad-spectrum antibiotics is started immediately • Treatment is shifted if necessary after a diagnosis is confirmed

Meningitis Listeria monocytogenes Signs and Symptoms

• Mild or subclinical infection in healthy adults • Nonspecific symptoms of fever, diarrhea, and sore throat • Elderly, immunocompromised, fetuses, and neonates • Affects the brain and meninges and causes septicemia • Death rate is 20% • Pregnant women are especially susceptible • Microbe crosses the placenta or postnatally through the birth canal • Intrauterine infections may result in premature abortion and death

Rubella Culture and Diagnosis

• Mimics other diseases and should not be diagnosed on clinical grounds alone • IgM antibody to the rubella virus can be detected early by ELISA or a latex-agglutination card • other conditions can lead to false positives, so testing should be augmented by acute and convalescent measurements of IgG • Women in developed countries routinely undergo antibody testing at the beginning of pregnancy to determine their immune status

Meningitis: Neisseria meningitidis Transmission and Epidemiology

• Neisseria meningitidis does not survive long in the environment • Usually acquired through close contact with secretions or droplets • Reservoir is humans harboring the pathogen in the nasopharynx • Carriage state lasting a few days to several months, exists in 3 - 30% of the adult population • Carriage rate exceeds 50% in institutional settings • Carriers living in close quarters with susceptible individuals more readily transmit the disease • Families, day care facilities • college dormitories, military barracks • Highest risk groups are 6 - 36 months old; 10 - 20 years old

• Cause transmissible spongiform • encephalopathies (TSEs)

• Neurodegenerative diseases with long incubation periods but rapid progressions • Human TSEs: Creutzfeldt-Jakob disease (CJD), others • Animal TSEs: scrapie, transmissible mink encephalopathy, bovine spongiform encephalopathy (BSE, or "mad cow" disease)

Impetigo Transmission and Epidemiology

• Not a serious disease, but highly contagious; children are the primary victims • transmitted by direct contact, via fomites, and mechanical vectors • peak incidence in summer and fall

Meningitis: Listeria monocytogenes Pathogenesis and Virulence Factors

• Not fastidious: resistant to cold, heat, salt, pH extremes, and bile • Grows inside host cells and can move directly from an infected host cell to an adjacent healthy cell

Passive immunity

• Occurs when an individual receives antibodies from another human or animal • Recipient is protected for a short period of time, even though they have not had prior exposure to the antigen • Lack of memory for the original antigen, lack of antibody production by the patient • Immediate onset of protection • Can be natural (e.g. breastfeeding) or artificial (injection) in origin • Useful when there is no effective treatment available or to treat immune deficiencies

Active immunity

• Occurs when an individual receives immune stimulus that activates B and T cells to produce immune substances such as antibodies • Creates memory that renders the person ready for quick action upon re-exposure to the same antigen • Requires several days to develop • Lasts for a relatively long time • Can be stimulated by natural or artificial means

Measles Transmission and Epidemiology

• One of the most contagious infectious diseases • Transmitted by respiratory droplets • Humans are the only reservoir • Person is infectious during the periods of incubation, prodrome phase, and the skin rash, but not during convalescence • Only large, dense populations of susceptible individuals can sustain a continuous chain necessary for transmission

CNS is "immunologically privileged"

• Only able to mount a partial, or different immune response when exposed to an immunological challenge • CNS functions are so vital that even temporary damage that could result from normal immune responses could be detrimental • Macrophages are present but not as active as in other body parts

Price of not vaccinating

• Outbreaks of measles, mumps, diphtheria, polio, typhoid fever, and whooping cough, which have been effectively controlled by vaccines • Decrease in the level of herd immunity, a phenomenon in which a certain percentage of the population is vaccinated, making it impossible for the microbe to circulate • Getting vaccinated serves the common good, as well as the individual good • Many young parents have no memory of the pre- vaccination era and don't appreciate the greater risk of not vaccinating their children

Meningitis: Streptococcus pneumoniae Prevention and Treatment

• Penicillin is not a good choice because the bacterium is often resistant • Ceftriaxone is used, but drug susceptibilities must always be tested • Two vaccines available • Prevnar: a seven-valent vaccine now recommended as a part of childhood immunizations • Contains capsular polysaccharide components of seven different serovars of Streptococcus pneumoniae • Pneumovax 23: 23-valent polysaccharide vaccine for adults

Antimicrobial peptides

• Positively charged peptides that act by disrupting the negatively charged membranes of bacteria • Play a major role in keeping the microbial count on the skin relatively low

Rubella Signs and Symptoms

• Postnatal rubella • Rash of pink macules and papules • Appears first on the face and progresses down the trunk and toward the extremities • Advances and resolves within 3 days • Adult rubella characterized by joint inflammation and pain rather than rash

Meningitis: Cryptococcus neoformans (Fungi) Transmission, epidemiology, treatment

• Primary ecological niche is the bird population • Present in areas where pigeons congregate, grow on bird droppings • Masses of dried yeast cells are scattered into the air and dust • Healthy humans have a strong resistance to it, i.e. opportunistic • Higher virulence rates of infection occur in patients with AIDS or that are otherwise immunocompromised (often fatal in these cases) • Treatment with a variety of antifungal drugs

Impetigo: Staphylococcus aureus Culture and Diagnosis

• Primary isolation is achieved by inoculation on blood agar • heavily contaminated specimens are plated on selective media such as mannitol salt agar

Measles Treatment

• Reducing fever, suppressing cough • Sustain nutrient, electrolyte, and fluid levels • Treatment of complications due to secondary infections • Vitamin supplements (vitamin A) appear to be helpful

Meningitis: Listeria monocytogenes Transmission and Epidemiology

• Reservoir is soil and water • animals, plants, and food are secondary sources of infection • most cases of listeriosis are associated with ingesting contaminated dairy products, poultry, and meat • pathogen isolated in 10 - 15% of ground beef, 25 - 30% of chicken and turkey carcasses, present in 5 - 10% of lunch meats, hot dogs, and cheeses

Rubella Causative Agent

• Rubivirus from the family Togaviridae • Nonsegmented single-stranded RNA virus with a loose lipid envelope • Humans are the only host • Virus has the ability to stop mitosis, an important process for a developing embryo and fetus • Induces apoptosis of normal tissue cells, causing irreversible harm to organs • Damages vascular endothelium, leading to poor development of many organs

Environment and Normal Biota of the Skin

• Skin is a dry, salty, relatively low pH (4-6) environment • Resident microbes must be capable of living in dry and salty conditions • Microbes are sparsely distributed over dry, flat areas of the skin • More dense populations in moist areas and skin folds • Also live in the protected environment of hair follicles and glandular ducts • Majority of species of the normal biota have not yet been cultured • Human Microbiome Project (HMP) is greatly expanding our knowledge of microbes found on the skin • Four major genera of microbes found on the skin... • Streptococcus • Staphylococcus • Propionibacterium • Corynebacterium

Meningitis: Streptococcus pneumoniae Causative Agent

• Small, gram-positive, flattened coccus in end-to-end pairs or short chains • Normal biota of the nasopharynx • Causes the majority of bacterial pneumonias • Most frequent cause of community-acquired meningitis • 25% of patients with pneumococcal meningitis will also have pneumococcal pneumonia • Most likely to occur in patients with underlying susceptibility

Measles Signs and Symptoms

• Sore throat, dry cough, headache, fever, conjunctivitis (inflammation of the conjunctiva, or outer layer of eye), lymphadenitis (enlargement of lymph nodes) • Red, maculopapularexanthem that erupts on the head and progresses to the trunk and extremities

Smallpox Transmission and Epidemiology

• Spread primarily through droplets • fomites such as contaminated bedding and • clothing can also spread the disease • Endemic in 31 countries in the 1970s • 10 - 15 million contracted the disease every year with 2 million fatalities/yr

Impetigo

• Superficial bacterial infection that causes the skin to flake or peel • Can be caused by either Staphylococcus aureus or Streptococcus pyogenes, (both Gram + cocci) or may be caused by a mixture of the two • S. pyogenes begins all cases of the disease, but later S. aureus takes over and produces a bacteriocin that destroys S. pyogenes

Meningitis Culture and Diagnosis

• Suspicion of bacterial meningitis constitutes a medical emergency • Differential diagnosis must be done with care and accuracy • Meningococcal meningitis must be confirmed or ruled out because it can be rapidly fatal • Treatment is begun with this organism in mind until it is ruled out

Smallpox Treatment

• There is no treatment for smallpox

Meningitis: Coccidioides species Pathogenesis and Virulence Factors

• True systemic fungal infection of high virulence • Pegins as a pulmonary infection, but can disseminate throughout the body • Coccidioidomycosis of the meninges is the most serious manifestation • All persons inhaling arthrospores probably develop some degree of infection, but some have a genetic susceptibility that gives rise to disease • Arthrospores develop into spherules in the lungs • Mild respiratory systems develop • Can develop into systemic disease, including meningitis

Smallpox Signs and Symptoms

• Variola major: highly virulent form causing toxemia, shock, and intravascular coagulation • Variola minor is a less virulent form • Important to recognize signs and symptoms of smallpox; diagnosis of a single case must be treated as an emergency • Prodrome period of high fever and malaise • Rash emerges in the mouth • Severe abdominal and back pain • Rash spreads throughout the body within 24 hours • Rash becomes pustular, crusts over, leaving nonpigmented sites pitted with scar tissue

Smallpox Causative Agent

• Variola virus, an orthopoxvirus • Enveloped DNA virus • This group also includes monkeypox and vaccinia • Hardy virus, surviving outside the host longer than most viruses

Types of vaccines

• Whole cell or virus vaccines • live, attenuated cells or viruses (most effective, least safe) • killed cells or inactivated viruses (safer, not always as effective) • Antigenic molecules derived from bacterial cells or viruses (subunits) • Safer still than whole-cell vaccines, but often not as effective • subunits derived from cultures of cells or viruses • subunits synthesized to mimic natural molecules • subunits manufactured via genetic engineering

Impetigo: Staphylococcus aureus Pathogenesis and Virulence Factors (cont'd) • Hyaluronidase

• digests the intracellular "glue" (hyaluronic acid) that binds connective tissue in host tissues • Staphylokinase • Digests blood clots • DNase, a nuclease that digests DNA • Lipase, an enzyme that helps the bacteria colonize oily surfaces

Basic principles behind vaccination

• stimulate a primary response and a memory response • prime the immune system for future exposure to a virulent pathogen • if the pathogen enters the body, the response will be immediate, powerful, and sustained • Vaccines have profoundly reduced the prevalence and impact of many infectious diseases that were once common and deadly • Ideally, a vaccine will activate both antibody and cell-mediated immune responses to the pathogen, but cause minimum damage/reaction to host; also produce memory so as to be long-lasting; stable, inexpensive

Signs and Symptoms Prenatal rubella

• teratogenic: causes harm to the fetus • virus is transmitted from the mother to fetus in utero, even if the mother is asymptomatic • infection in the first trimester can result in miscarriage or multiple permanent defects • most common defect is deafness, but cardiac abnormalities, ocular lesions, and mental and physical retardation can occur in varying combinations • other sequelae include anemia, hepatitis, pneumonia, carditis, and bone infection