BIO241 – MICROBIOLOGY
Bacterial & Fungal Infections – Chapters 21-26
Infectious Diseases Affecting the Skin and Eyes
· Acne
o epidemiology: Propionibacterium acnes; normal bacterial microbiota; up to 85% of adolescents suffer from acne at some time
o pathogenesis: hair follicle infection that spreads into surrounding tissue, generating an abscess; complications - skin disfigurement (scars)
o treatment: tetracycline, blue light therapy, oral contraceptives, vitamin A derivatives (Retin A cream ... can cause dry skin; Accutane, an oral medication which is unfortunately also a teratogen (it causes birth defects, so it should not be used by pregnant women) ... Accutane may be linked to psychiatric problems, including a potential risk for suicide; Americans spend ~$1 billion/year on prescription drugs to treat acne
o prevention: decrease sebum accumulation by thorough personal hygiene and depress bacterial growth with topical peroxide-containing medications
· Impetigo
o epidemiology: Staphylococcus aureus and/or Streptococcus pyogenes; this bacterial disease is highly contagious in children
o pathogenesis: superficial infection leads to formation of thin-walled abscesses that look like blisters or "weeping" lesions with scabs; complications - "blood poisoning" (toxemia or septicemia)
o treatment: bacitracin salve or other antimicrobial agents resistant to bacterial enzymes that destroy penicillins
o prevention: personal hygiene; avoid contact with lesions on other people
· Furuncle (boil)
o epidemiology: Staphylococcus aureus; normal bacterial microbiota in up to 30% of normal humans
o pathogenesis: infected skin follicle leads to formation of an abscess; complications - multiple abscesses (carbuncles); "blood poisoning" (toxemia) due to systemic distribution of toxin or bacteria; osteomyelitis
o treatment: "lance" abscess; treat with bacitracin, vancomycin or other antimicrobial agents that are resistant to bacterial enzymes that destroy penicillins
o prevention: personal hygiene; avoid contact with boils on other people; newly-developed vaccine StaphVAX
· Necrotizing Fasciitis
o epidemiology: Streptococcus pyogenes (bacterium); according to CDC, there were 500-1500 cases in the US in 1996 and 20% were fatal
o pathogenesis: rapidly-spreading infection leads to destruction of tissues at sites of infection ... aka Flesh-Eating Disease; complications - formation of abscesses throughout the body and "blood poisoning" (toxemia or septicemia)
o treatment: penicillin, erythromycin, or tetracycline; surgery, when necessary
o prevention: personal hygiene
· Candidiasis
o epidemiology: Candida albicans, this dimorphic fungus is a member of the normal microbiota; likelihood of developing disease is enhanced by chronic skin moisture, especially in immunosuppressed individuals (AIDS, diabetes, etc.)
o pathogenesis: as Candida grows on the skin, it induces a bright red inflammation, blister-like superficial lesions or more severe lesions all of which are perhaps related to hypersensitivity; it sometimes occurs around the mouth (angular chelitis); complications include systemic infection, which can lead to fulminating disease and death
o treatment: clotrimazole, miconazole or nystatin for skin infections; oral ketoconazole for systemic infections
o prevention: avoid excessive skin moisture, immunosuppression
· Tineas (Ringworm)
o epidemiology: dermatophytic fungi such as Epidermophyton, Microsporium, or Trichophyton; prevalent in athletes
o pathogenesis: superficial skin infection causes granulomas on head/scalp (tinea capitis), groin (tinea curis), body (tinea corporus), foot (tinea pedis)
o treatment: lamisil (terbinafine-HCl cream ... topical); shampoo containing selenium; ketoconazole or itraconazole for initial antimicrobial agent therapy; griseofulvin (oral) for chronic infections
o prevention: avoid contact with lesions on other people's skin
o prevention: Varicella vaccine (more vaccine info); avoid contact with respiratory secretions of infected persons; varicella-zoster immune globulin (VZIG)
· Keratitis
o epidemiology: Staphylococcus aureus (bacterium), Aspergilus (fungus), Herpes simplex virus, Acanthamoeba (protozoan) transmitted by contact with contaminated water or objects; ~30,000 cases per year in the US, especially in contact lens wearers
o pathogenesis: infection results in inflammation and eventual formation of corneal ulcers, which can result in scar tissue formation (and may lead to blindness) if left untreated
o treatment: antibiotic, antiviral or antifungal ointments (plus cortocosteroids in some cases)
§ bacterial keratitis - fluoroquinolones
§ herpetic keratitis - acyclovir ointment
§ Acanthamoeba keratitis - chlorhexidine or polyhexamethylene biguanide (PHMB) in combination with propamidine isethionate and neomycin
o prevention: avoid contact with infected people or objects contaminated with any or these infectious agents
Infectious Diseases Affecting the Nervous System
· Meningitis
o epidemiology: Streptococcus pneumoniae (affects children most); Haemophilus influenzae (this bacterium mostly affects children 6 months to 2 years old); Neisseria meningitidis (~2500 cases per year ... affects young adults most); Listeria monocytogenes (actually infects via the gastrointestinal tract, but ends up causing the same syndrome as the others) - all these microbes are bacteria, but viruses and fungi can also cause meningitis; ~8000 cases of aseptic (viral) meningitis per year in the US
o pathogenesis: damage to meninges (headache, coma) - complications include disseminated intravascular coagulopathy (DIC), kidney and skin damage (purperal lesions), death (~250 per year in the US)
o treatment: ampicillin (Haemophilus); penicillin (Listeria, Neisseria, and Streptococcus); amphotericin B (fungi); TLC, symptomatic relief (viruses)
o prevention:
§ vaccines
§ Hib vaccine induces immunity against meningitis caused by Haemophilus influenza b
§ Menomune induces immunity against major strains of Neisserial meningitis
§ Prevnar protects against Streptococcal meningitis
§ avoid contact with respiratory secretions of others
· Encephalitis
o epidemiology: Encephalitis viruses are transmitted by mosquitoes (Culex tarsalis; others); reservoirs are other animals, including birds, reptiles and horses; infection is most prevalent in Summer and Fall; ~600 primary cases of encephalitis (not including West Nile) per year in the US (~100 post-infection cases); West Nile Fever is a recently emerging encephalitic disease in the US, with 9862 cases reported to CDC in 2003; we spend ~$150 million per year trying to minimize encephalitis virus transmission
o pathogenesis: mosquito "injects" virus into bloodstream; virus replicates in the CNS, causing fever and headache, vomitting,stiff back and neck, drowsiness, tremors, loss of coordination, convulsions, seizures; complications - may lead to coma as a result of CNS damage (can lead to retardation, paralysis) and death occurs in 1-60%, depending upon the virus responsible
o treatment: TLC ... management of symptoms and complications; FDA has recently approved alpha-interferon as a possible treatment for West Nile Fever
o prevention: vaccines (none for West Nile Fever); mosquito repellent use; mosquito control
· Tetanus
o epidemiology: Clostridium tetani; endospores of this bacterium enter body via animal bites, scratches, puncture wounds; fewer than 10 cases per year in US
o pathogenesis: toxin (tetanospasmin) causes CNS damage (4-21 days); complications - respiratory failure causes death (70% of patients die)
o treatment: antitoxin; penicillin; valium, barbituates (minimize damage)
o prevention: antitoxin, vaccine (DPT vaccine @ 2, 4, 6, 18 months and Td vaccine boosters at 7-10 year intervals)
· Botulism
o epidemiology: Clostridium botulinum - foods contaminated with spores (from soil) and improperly canned; ~20 cases per year in US
o pathogenesis: after 12-36 hour incubation period, exotoxin (botulin) causes flaccid paralysis of neck and chest, which can cause death (up to 70% of untreated cases; ~5% of treated cases) due to cardiac and/or respiratory failure (Did ya know ... infant botulism is an infectious disease transmitted by infants eating nonpasteurized honey, which contains Clostridium botulinum spores?)
o treatment: antitoxin (available from CDC)
o prevention: avoid ingestion of contaminated foods via better food washing and canning techniques (sanitation)
· Toxoplasmosis
o epidemiology: Toxoplasma gondii (protozoan) infection occurs via oocysts transmitted via cat feces or tissue cysts transmitted by eating undercooked meat, especially pork, lamb or venison; >20% of adults in US and >30% of world population have been infected
o pathogenesis: cysts develop into tachyzoites in intestines, invade the intestinal lining and multiply in the intestinal cells, then spread throughout the body to multiply in other cells, causing disseminated infection that leads to chronic fatigue, fever, malaise, sore throat, headache, muscle pain, swelling of spleen, liver, and lymph nodes; these signs and symptoms last several weeks, then subside as the immune system controls (but does not eliminate) the infection; some people are asymptomatic; complications include chronic latent infection often with neurologic or retinal disease (retinochoroiditis); birth defects if infected during third trimester of pregnancy; this disease is a big problem in AIDS and other immunocompromised patients
o treatment: pyrimethamine and sulfadiazine, plus folinic acid.
o prevention: cook meat to safe temperatures; avoid cat feces (pregnant women should not clean cat litter boxes)
Infectious Diseases Affecting the Cardiovascular and Lymphoid Systems
· Septicemia and Septic Shock
o epidemiology: numerous bacteria, including: Gram-negative bacteria such as Escherichia coli, Salmonella typhi, Neisseria meningiditis, Yersinia pestis and many others; several Gram-positive bacteria, such as Staphylococcus aureus, Streptococcus pyogenes, and Bacillus anthracis; these bacteria enter and grow in the bloodstream as a result of food borne infections as well as iatrogenic infections contracted in hospitals (nosocomial infections) and other health care facilities where indwelling catheters and/or intravenous feeding tubes are often used; death rate for septicemia has been increasing recently; as many as 500,000 cases each year in the US, causing 31,224 deaths in 2000, making it the number 10 killer in the country
o pathogenesis: bacteria enter the bloodstream from sites of infection and multiply there (septicemia ... aka "blood poisoning"), releasing toxic substances (endotoxin, cell wall breakdown products) that trigger neutrophils (PMNs) to release cytokines that cause fever and inflammation; this leads to skin lesions (due to hemorrhage, disseminated intravascular coagulopathy (DIC), and lymphangitis (localized red streaks representing inflammed lymph vessels)) and systemic vascular permeability which causes leakage of fluid into the tissues that leads to decreased blood pressure (hypotension) and brings on hypovascular shock (septic shock) as a result of lack of blood flow to vital organs (signs and symptoms include chills and fever (and acute respiratory disease if the lungs are involved); this leads to shutdown of one vital organ after another, which can cause death; complications include meningitis, encephalitis, limb loss; death ... untreated septic shock is 40-60% fatal
o treatment: early diagnosis and effective treatment with antibiotics can intervene in the development of this disease; if diagnosed too late, antibiotic therapy can actually enhance development of septic shock because it can cause release of bacterial toxins into the bloodstream
o prevention: avoidance of contamination of indwelling catheters and intravenous feeding tubes; early diagnosis and effective treatment with antibiotics (this is a problem these days because many hospitals have been decreasing their clinical microbiology laboratory services in an effort to save money)
· Anthrax
o epidemiology: Bacillus anthracis, an endospore-forming soil bacterium; this zoonotic disease primarily affects grazing animals such as cattle, sheep and goats, but can be transmitted to humans by contact with the endospores, either via skin wounds or by inhalation; this disease is considered to be a good candidate for biological warfare, and has been used in terrorist activities ... view a set of online CDC videos on bioterrorism
o pathogenesis: as endospores germinate, the vegetative bacterial cells begin to produce a necrotizing toxin that causes development of pustular lesions called eschars characterized by necrotic centers that will eventually be filled with black fluid; complications include fulminating septicemia that frequently leads to death, especially from the pulmonary form of the disease characterized by necrotic centers that will eventually be filled with black fluid; complications include fulminating septicemia that frequently leads to death, especially from the pulmonary form of the disease
o treatment: penicillin ... cipro (ciprofloxacin) was approved in 2000
o prevention: vaccine; avoid contact with endospore-contaminated articles such as unwashed or unsterilized wool, goat hair, cattle hides, etc.
· Gangrene (myonecrosis)
o epidemiology: Clostridium perfringens; wound is infected with endospores of this bacterium from soil, clothing, etc.
o pathogenesis: superficial infection leads to cellulitis, then to myonecrosis due to toxins; complications - death due to CNS damage caused by toxins (sometimes complicated by gas formation, hence the name "gas" gangrene)
o treatment: debridement, penicillin; hyperbaric chamber (exposure to very high concentrations of oxygen kills this anaerobe)
o prevention: early treatment may prevent full-blown disease
· Plague
o epidemiology: Yersinia pestis; this bacterium is transmitted by rat fleas; endemic in many places throughout the world, including Southwestern US (in prairie dogs, especially in the southern regions of the west); 10-20 human cases per year in the US; 1994 epidemic in India led to ~700 cases and ~60 deaths
o pathogenesis: infects and kills macrophages; whole body (liver, spleen, lymph nodes (buboes), lungs, meninges, skin) damaged, causing fever and massive blood clotting, which leads to shock, which may cause death (major complication)
o treatment: streptomycin or tetracycline
o prevention: vaccine; control rats and fleas; avoid contact
· Lyme Disease
o epidemiology:
§ Borrelia burgdorferi (bacterium) is spread by the nymph stage (poppy-seed sized) of deer (black-legged) ticks ... it takes ~36 hours for the tick to infect you with enough bacteria to cause disease
§ reservoirs are white-tailed deer and white-footed mice
§ 15,000 cases reported in the US each year, mostly in children 2-15 and adults 30-55 years old who live in the Northeast and upper Midwest (more epidemiology)
§ Lyme disease was first discovered near Lyme, CT
§ most frequently diagnosed tick-borne disease in the US
o pathogenesis: - 60-85% of patients develop an expanding, ring-shaped ("Bull's-eye") red rash (erythema chronicum migrans or ECM) at the site of a tick-bite ... after 3 days to one month; accompanied by flu-like symptoms (malaise and fatigue, headache, fever and chills, nausea, muscle and joint pain, neck stiffness) and patients may develop secondary skin lesions, facial paralysis, forgetfulness; chronic, untreated systemic infection leads to arthritis, heart inflammation, neurological abnormalities (weeks to months); nerve demyelination may lead to multiple sclerosis-like symptoms (years after infection)
o treatment: ceftin (cefuroxime axetil), penicillin or tetracycline (after diagnosis with a newly-approved test kit, "PreVue B"); although there is controversy, it appears that long-term intravenous antimicrobial agent therapy may be required in chronic cases
o prevention: vaccine ("LYMErix") has been approved for people from age 15 to 70, but not for those under 15 ... not 100% effective, so it is still important to avoid tick-bite (wear protective clothing, use tick repellent, remove attached ticks)