Fungi fundamentals
• Occupy almost every ecological niche• Exist in two forms:• Yeasts
– Single celled
• Molds– Growth in branching chains called hyphae
• Dimorphic– Have both yeast and mold life stages
Fungi fundamentals
• Life stages• Mold in soil• Yeast in tissues• Mold phase produces spores that
spread the organism in the environment and also cause infection
Diagnosis and Identification
• PCR• Use of immunological techniques to
identify antibodies to infection in people
• Microscopy and culture• Identification by visual examination
of appearance
Fungal pathogenesis
• Some fungi produce mycotoxins• Grow in tissue, spread through organs• Superficial infections• 1Skin• Systemic infections (disseminated)
– Most severe kind– Immunosuppressed people are at high
risk
Coccidioidomycosis
• Valley fever• Agent: Coccidioides immitis• Reservoir: soil• Arid climates• Endemic to southwestern US
– Arizona and California
• S. America– Brazil, Colombia, Mexico, Venezuela
Coccidioidomycosis
• Infection is by inhalation of arthroconidia• Arthroconidia
– Spores that form from segments of the hyphae
• Become airborne when dust is disturbed• Inhaled, infection begins in the lungs• Once in tissues, fungus forms spherules
(spherical cells) and reproduces
Disease process
• Initial infection via the lungs• May be asymptomatic
– Probably very common in endemic areas
• May cause flulike symptoms• For many people with healthy immune
systems, infection is self-limiting• Confers long-term immunity• May leave calcified lesions in the lungs
Disseminated infection
• About 1% of symptomatic infections become disseminated
• Most dangerous type of infection• Fatal without treatment• Growth in body tissues
– Skin– Bone – Meninges
• More common in immunosuppression
Diagnosis
• Visualization of spherules under the microscope
• Culture of fungi from tissue samples in the laboratory
• Handling of the spores is high-risk; laboratory acquired infection is an occupational hazard for people who work with valley fever
Treatment
• Antifungal drugs• Amphotericin B
– Produced by bacteria (Streptomyces)– Effective, but quite toxic– Kidney damage– IV administration
• Newer drugs: Azoles– fluconazole
Cryptococcus
• Cryptococcal meningitis• Agent: Cryptococcus neoformans• Reservoir: soil• Infection by inhalation• Primary site of infection is the lungs• Can disseminate from there
Cryptococcus
• Humans are fairly resistant• Severe infection is seen in
immunocompromised individuals• Opportunistic infection of AIDS• Cases have tended to follow the
pattern of AIDS epidemics in a given area
Cryptococcus
• Diagnosis by visualization in CSF• Confirmation by culture or
observation of growth in histological samples
• Treatment• Amphotericin B + 5-flucytosine• Maintenance therapy with
fluconazole
Histoplasmosis
• Agent: Histoplasma capsulatum• Reservoir: soil• Soil contaminated by birds is high risk• Primary infection is in the lungs• Different disease courses
– Self-limiting– Systemic – Chronic pulmonary
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