2-32 Fungi II Flashcards
What are the four major categories of fungal infection?
What are some recurring themes for superficial mycoses?
Caused by fungal growth on the superficial skin layer
- Does not require thermal dimorphism: often growing on cool exterior as hyphae
- Very common, but symptoms are minor: itch or discoloration
- Treated with topical azoles, alt oral griseofulvin
What is the pathogenesis of superficial mycoses?
Caused by dermatophytes (AKA dermatophytoses)
Infect only superficial keratinized structures
- Skin
- Hair
- Nails
▪ Form chronic infections in warm, humid areas on body surface
▪ Inflamed circular border of papules and/or vesicles, broken hairs, thickened, broken nails
▪ Skin within border may be normal
▪ Named for affected body part:
Tinea capitis (head)
Tinea corporis (ringworm)
Tinea cruris (Jock itch)
Tinea pedis (Athlete’s foot)
▪ Transmitted by fomites or by autoinoculation from other sites on body
How are superficial mycoses diagnosed, treated, and prevented?
Exam: itching, redness, history of tight or wet clothing
Microscopic exam
Scraping from affected skin or nail
Treat w/ 10% KOH
Examine remains for hyphae & spores
Culture on Sabouraud’s agar at room temp
Microsporum show fluorescence when examined under Wood’s lamp
Topical antifungal cream
Terbinafine (Lamisil)
Undecylenic acid (Desenex)
Miconazole (Micatin)
Tolnaftate (Tinactin)
Note: treat all affected body sites simultaneously
Alt: oral griseofulvin (Fulvicin)
Keep skin dry and cool
What are some recurring themes for subcutaneous mycoses?
- Introduced by trauma exposing subcutaneous tissue to soil or vegetation
- Slow spread trauma site → trunk by lymphatics
- Thermal dimorphism
- Patient presents with history of ineffective antibiotic treatment
- Treated with oral azoles
- In serious cases, may begin with a short course of amphotericin B and surgery
What is an example of an organism that causes a subcutaneous mycosis?
What is the pathogenesis of subcutaneous mycoses?
▪ Introduced into skin by thorn puncture
▪ Yeasts grow at site and form painless pustule or ulcer
▪ Draining lymphatics form suppurating subcutaneous nodules
▪ Symptoms wax and wane over years
▪ May progress to disseminated disease and meningitis if immunosuppressed
▪ Patients with COPD and long term corticosteroid use may develop pulmonary symptoms from inhaling the spores; difficult to distinguish from TB or histoplasmosis
How are subcutaneous mycoses diagnosed?
▪ Painless pustule or ulcer on hand or arm: reddish, necrotic, nodular papules may extend along lymphatic from initial injury site
▪ History of gardening, farming, landscaping, berry-picking
▪ History of ineffective antibiotic treatment
▪ In AIDS, may see nodules disseminated over whole body
▪ In COPD+alcoholism, respiratory distress
Tissue biopsy: round or cigar-shaped budding yeasts – hard to see
Culture at room temp from pus, biopsy: hyphae with oval conidia in clusters at tip of slender conidiophores (resembles a daisy)
How are subcutaneous mycoses treated and prevented?
Treatment: 3-6 months itraconazole (Sporanox) or other oral azoles for normal form of disease
For more serious types, admit for Amphotericin B
Prevention: garden gloves
What are some recurring themes in systemic mycoses?
- Environmental: spores/fungi in soil
- Inhaled into lungs
- Thermal dimorphism
- Wide range of severity: asymptomatic clearance to death
- NOT person-to-person transmissible
- Coccidioides/Histoplasma/Blastomyces: mimic TB
- History: American dirt, not foreign crowds
What is an example of an organism that causes systemic mycosis?
- Coccidioides = coccidioidomycosis
- Coccidioides immitis and C. posadasii
- Dimorphic: mold in soil, spherule in tissue
- Grow in the rainy season as mycelia (noninfectious)
- In the dry summer, forms hyphae with alternating arthrospores and empty cells
- When disturbed by wind or excavation, readily release arthroconidia (infectious)
- Spores are carried by the wind, inhaled by humans
- Endemic in southwest US and Latin America; may travel home in returning patient or arrive in contaminated shipped material
Caseload has spiked in this century as endemic areas have become (geriatric!) population centers
What is the general pathogenesis of coccidioides?
Arthrospores (arthroconidia) are inhaled: Infectious dose can be as low as a single IU, though high dosage is more likely to cause symptoms
Within terminal bronchiole, change form
- Spherules: highly resistant to eradication by immune sys
- 30um diameter
- Thick, doubly-refractive wall
- Filled with endospores
- Wall ruptures to release endospores, develop into new spherules
- Spherules and endospores are not infectious
Symptomatic disease may appear as Valley fever or desert rheumatism
•May affect any organ; primarily seen in bones and meninges
•
•Induces immune anergy; May be rapidly fatal
What are the phases of coccidioides infection?
Acute phase: Innate immunity (macrophage response) attempts to clear infection: often successful
Chronic phase: Innate immunity inadequate for clearance; lymphocytes and histiocytes initiate granuloma and giant cell formation (containment).
If CMI is healthy, infection is contained in granulomas in lung; many eventually cleared asymptomatically
Many patients who become ill have nonspecific flulike symptoms that resolve at home (~60% exposures = asymptomatic+flulike)
What are risk factors for coccidioides infection?
•advanced age, immunocompromise, late-stage pregnancy, occupational high-level exposure (farmers, construction workers, archaeologists), black or Filipino race
How is coccidioides infection diagnosed?
- Workup for pneumonia, meningitis
- Take biopsies of relevant tissues, CSF, blood, urine, stain with H&E or fungal stains; examine microscopically for spherules
- Cultures on Sabouraud’s agar at 25C: cottony white mold composed of hyphae with arthrospores: cultures are infectious! Handle in Biosafety Level 3
- Serology for exposure, titers: (IgG from blood and/or CSF) titer spikes if disseminating. Positives are very reliable, but some false negatives occur
