Medical Mycology Flashcards
Fungal infections of the skin, hair, and nails
Dermatophytoses
Latin for “worm”
Tinea
Three sources of dermatophytoses
Geophillic, Zoophillic, Anthrophillic
Geophillic dermatophytoses
From soil; inflamatory, severe, and short duration
Zoophilic dermatophytoses
From animals; inflamatory, severe, and short duration
Anthrophillic dermatophytoses
Only grow on humans; non-inflamatory, mild, and chronic.
Three genera of Ascomycetes that cause dermatophytoses
Epidermophyton, Microsporum, and Trichophyton
Epidermophyton
Skin and rarely nails, NOT hair
Microsporum
Hair and skin, NOT nails
Trichophyton
Hair, skin, and nails
Ringworm of the scalp
Tinea capitis; infection from small animals, theater seats, and barber tools
Jock itch
Tinea cruris; spread by shared bathing facilities or through contact with other lesions
Athlete’s foot
Tinea pedis; Usually spread by bare feet in gyms and locker rooms
Nail fungus (onychomycosis)
Tinea unguium
Onychomycosis
nail fungus; spread by pedicure tools
The demographic most commonly affected by onychomycosis
The elderly
What kind of treatments are available for most dermatophytes
Most treatments are topical, with the exception being nail fungus which is oral
Ringworm of the body
Tinea corporis
Geophillic and zoophillic Tinea corporis infection symptoms
Vesicles and pustules on skin
Anthrophillic Tinea corporis infection symptom
“topographical map” appearance with an area of central clearing
The populations most likely to contract Tinea coproris
The immunosuppressed, people with outdoor occupations, people who work closely with animals, and people who play contact sports
Ringworm of the beard genus, species, transmission and treatment
Tinea barbae, transmitted via razors in barber shops and animals. Requires oral antifungals
Methods for diagnosing dermatophytoses
Wood’s light, scraping + KOH treatment, and culture on Sabouraud’s Dextrose agar
What is a “wood’s light”
A UV light used to diagnose dermatophytes, which fluoresce
The media most commonly used to grow fungal cultures
Sabouraud’s Dextrose agar
How do dermatophytes grow in tissue
as hyphae
How are organisms that cause dermatophytoses identified
by morphology of conidia and colony color
How are people usually infected by subcutaneous mycoses
By walking around barefoot and having skin punctured by something with spores on it
What is the classification of most subcutaneous mycoses
Saprophytic ascomycetes
Three types of subcutaneous mycoses
Chromoblastomycosis, Mycetoma, and Sporotrichosis
Chronic nodular, warty lesions on lower extremities
Chromoblastomycosis
Madura foot with osteolytic changes
Mycetoma
Ulcerous lesions that spread lymphatically
Sporotrichosis
The most common fungus that causes Chromoblastomycosis
Fonsecaea pedrosoi
Population most likely to contract chromoblastomycosis
barefoot people in hot, dry areas of Mexico and South America
Symptoms of Chromoblastomycosis
Nodular, verrucous lesions that resemble cauliflower, usually on lower extremities
Dematiaceous
black pigmented
Treatment for Chromoblastomycosis
Nonexistent. Surgery to remove lesions is 30-50% effective
Fonsecaea pedrosoi grows which way in soil and which way in tissue
filamentous bodies in soil, yeast (sclerotic bodies) in tissue
Fungus that is most common cause of mycetoma
Madurella mycetomatis
Symptoms of Madura foot
Tumors, draining sinuses with black granules containing compacted hyphal bodies, destructive to adjacent tissues and bone
Population most likely to contract Madura foot
people walking barefoot in hot, dry areas with low rainfall
How does Madurella mycetomatis grow in soil versus in tissue
It grows as grains of compacted hyphal colonies both in tissue and in culture
Recommended treatment for Madura foot
Treatment with antifungals for 6 months, then surgery
The fungus that causes sporotrichosis
Sporothrix schenkii
Thermally dimorphic
the fungus grows as a saprophytic mold at 25 degrees Celsius and as a parasitic yeast at 37 degrees celsius
Symptoms of sporotrichosis
Begins as a nodule that opens to a draining sinus, moves up the body through the lymphatic system, making an archipelago of new nodules and sinuses
Treatment for Sporotrichosis
Supersaturated KI solution in increasing doses 3x daily is 90% effective OR oral antifungals
Four systemic mycoses (all ascomycetes)
Histoplasmosis, Blastomycosis, Coccidioidomycosis, Paracoccidioidomycosis
The most common endemic mycosis in the U.S.
Histoplasmosis
The fungus that causes Histoplasmosis
Histoplasma capsulatum
Where is Histoplasmosis most common
The Ohio-Mississippi river valley, where there are a lot of starlings
How does Histoplasma capsulatum grow in the lungs versus in the environment
Grows as a yeast in the lungs, as hypha with spiny macroconidia in the environment
How someone gets infected with Histoplasma capsulatum
Inhaling the infectious microconidia
Two symptoms of Histoplastmosis
Capsules in the lung; tuberculosis-like symptoms
Two diagnostic tools commonly used for Histoplasmosis
Chest x-rays and skin tests w/histoplasmin
How do immunocompromised people fare with Histoplasmosis
They do not clear it on their own
The fungus that causes Blastomycosis
Blastomyces dermatitidis
Where is Blastomycosis endemic
the Eastern United States
Symptoms of Blastomycosis
Pneumonia, cutaneous lesions on skin
How do the immunocompromised fare with Blastomycosis
They do not clear it without antifungals
What is the most endemic mycosis in the United States
Coccidioidomycosis
The fungus that causes Coccidioidomycosis
Coccidioides immitis
How does coccidioidomycosis grow in the environment versus in tissue
Grows as hyphae with arthroconidia in the environment and as sporangia in the lungs
Fungus that causes Valley Fever
Coccicidioides immitis
Where is Valley Fever endemic
The lower Sonoran life zone
Symptoms of Valley Fever
Pneumonia; 5% develop lung nodules, which can spread to all organs of the body, skin, bones, joints, and meninges
Valley Fever: Healthy people vs Immunocompromised
In healthy people, usually resolves spontaneously; in immunocompromised, disseminated coccidioidomycosis develops
Diagnostic tests for Valley Fever
Chest x-ray and skin test
The fungus that causes paracoccidioidomycosis
Paracoccidioides brasiliensis
How does Paracoccidioides brasiliensis grow in tissue versus in the environment
In tissue, grows as a waxy yeast colony. In the environment, grows as a mold colony
What is indicative of a paracoccidioidomycosis infection
The “ship’s wheel” yeast
Where do Paracoccidioidomycosis infections usually occur
Latin America, 80% of cases found in Brazil
Symptoms of Paracoccidioidomycosis
Lung problems, grossly deforming lesions on mucous membranes of mouth, nose and GI tract
How is Paracoccidioidomycosis treated
A combination of fungistatic drugs and sulfonamides
Opportunistic mycoses
Fungi that only cause disease in debilitated patients
Basidiomycete anamorphic that causes cryptococcosis
Cryptococcus neoformans
Two virulence factors for Cryptococcus neoformans
The polysaccharide capsule (key factor) and melanin that resists killing oxidation produced by phagocytes
Where is Cryptococcus neoformans found
in pigeon poop
How someone becomes infected with Cryptococcus neoformans
Inhaling the basidiospore and yeast
How does an infection with Cryptococcus neoformans manifest in immunocompromised
Cryptococcal meningitis and skin lesions
Ascomycete anamorphic that is the major fungal pathogen of man
Candida albicans
How does Candida albicans grow in the body
As a commensal yeast and/or a parasitic mold
The first “red flag” disease for HIV that appears
Oral candidiasis (thrush)
A fungus that is part of the normal flora of the mouth, GI tract, skin, and vagina
Candida albicans
Symptoms of chronic mucocutaneous candidiases
multiple infections with Candida albicans which result in disfiguring granulomas
What is the treatment for chronic mucocutaneous candidiasis
there is no treatment
Ascomycete that causes pneumocystis pneumonia
Pneumocystis jiroveci
Where in the world is Pneumocystis jiroveci found
Everywhere!
Symptoms of Pneumocystis pneumonia
diffuse pneumonia
Treatment for pneumocystis pneumonia
Trimethoprim-sulfamethoxazole
Why are most antifungals ineffective against Pneumocystis
It lacks ergosterol, which is the target of most antifungals
How is Pneumocystis pneumonia diagnosed
Collecting samples via broncoalveolar lavage, then examining them for folded, saggy asci
Group of fungal infections caused by a variety of zygomycete molds
Mucormycosis
The most common cause of mucormycosis (zygomycete)
Rhizopus oryzae
Symptoms of mucormycosis
Rapid onset of tissue necrosis
Two populations of patients at risk for developing mucormycosis
Burn patients and patients with diabetic ketoacidosis
How does mucormycosis grow in tissue
it grows as hyphae
Treatment options for mucormycosis
Surgical removal of the entire infected area. The high doses of the antifungals required to treat this are highly nephrotoxic
The fungus that most commonly causes Aspergillosis
Aspergillus fumigatus
Fungus ball
a “ball” of fungal hyphae
Aspergilloma
a fungus ball
How serious is disseminated aspergillosis
95% fatal
Griseofulvin
Interferes with microtubule assembly, inhibiting hyphal growth and mitosis
Terbinafine
Inhibits ergosterol synthesis
Azoles
Ergosterol biosynthesis inhibitors
Polyenes
binds to ergosterols to rearrange them to form a hydrophilic pore
5-Fluorocytosine
Blocks DNA synthesis
Echinocandins
inhibit gluten synthase, so osmotic integrity is lost
Limitations of griseofulvin and terbinofines
only work on dermatophytes and keratinized tissues
Problem with azoles
Resistance: some fungi exclude the uptake of azaleas, develop altered membranes, or alter the binding site
Problems with polyenes
toxicity
Problems most encountered with 5-fluorocytosine
Resistance develops quickly
What are Echinocandins
Fungal secondary metabolites
What shape are echinocandins
cyclic hexapeptide core with a lipid side chain
