Fungal Infections Flashcards
Tinea - What organisms are responsible?
Trichophyton tonsurans (Most common)
Microsporum canis
Trichophyton rubrum
Tinea cruris - What organism is responsible?
Trichophyton rubrum
Tinea pedis (Hyperkeratotic form) - What organism is responsible?
Trichophyton rubrum
3 presentations of tinea unquium (onchomycosis)
Leukonychia mycotica Subungual onchomycosis (distal vs. proximal)
Culture media used to dx fungal infections (2)
Sabouraud’s agar
Dermatophyte Test Medium (DTM) = Sabouraud’s + antibiotic + pH color indicator
Risk factors for Candidiasis
Antibiotics Corticosteroids Diabetes Mellitus Oral contraceptive pills Pregnancy Burns Trauma Foreign body (catheters) Immunosuppression
Tinea versicolor
Caused by Malassezia furfur - normal yeast flora of skin and scalp; feeds on sebaceous lipids
Presents as asymptomatic yellow/brown scaly patches; less commonly as hypopigmented patches or folliculitis
Treatment: Topical miconazole
Sporotrichosis - Causative organism
Sporothrix schenckii
Sporotrichosis - Clinical Presentation and Treatment
Traumatic innoculation of spores into skin (typically by a thorn) causes lymphocutaneous disease characterized by local ulcer with nodules along draining lymphatics (ascending lymphangitis)
Treatment: Itraconazole, potassium iodide
4 classic dimorphic fungi
Blastomycosis
Coccidiodomycosis
Paracoccidioidomycosis
Histoplasmosis
Blastomycosis
Etiology: Blastomyces dermitiditis
Epidemiology: Mississippi-Ohio River Valley and Central America
Causes inflammatory lung disease; can disseminate to skin and bones, and can form granulomatous nodules
Coccidiodomycosis
Etiology: Coccidiodes immitus
Epidemiology: Saprophyte found in Sonoran environments; associated with occupational exposure (agriculture, military, construction)
Causes pneumonia and meningitis; +/- cavitary / granulomatous lung nodules; can disseminate to skin and bone
Paracoccidioidomycosis
Etiology: Paracoccidioides brasiliensis
Epidemiology: Saprophyte common to Central/South America
Causes pneumonia; can disseminate to involve skin, lymph nodes, and adrenals
Histoplasmosis
Etiology: Histoplasma capsulatum
Epidemiology: Soil saprophyte a/w bird and bat feces; common to chicken farms and caves in the MS-OH River Valley
Causes pneumonia +/- chronic pulmonary cavitations; rarely disseminates causing oropharyngeal ulcers and adrenal involvement
Cryptococcicosis
Etiology: Cryptococcus neoformans; mucoid capsule Serotype A responsible for 95% of infections in the US
Epidemiology: Worldwide; a/w pigeon feces
Causes cryptococcal meningitis, an AIDS-defining illness (CD4 < 50)
Aspergillosis
Etiology: Aspergilus fumigatus
3 major presentations:
- Invasive aspergillosis (immunocompromised)
- Allergic bronchopulmonary aspergillosis (asthma, CF); causes bronchiectasis and eosinophilia
- Aspergillomas in lung cavities (esp. after TB)
Some species produce aflatoxins, which are associated with hepatocellular carcinoma
Why does mucormycosis preferentially affect diabetics in DKA?
Rhizopus sp. are thermotolerant, thrive in high concentrations of glucose and ketones, and prefer acid pH
Organisms can proliferate in blood vessels walls when there is an excess of glucose and ketones and penetrate the cribriform plate to enter the brain
Mucormycosis
Etiology: Rhizopus sp.
Epidemiology: Ubiquitous in decaying organic matter
Presentation is acute and severe with 50% mortality; pre-deliction for diabetics in DKA
Fungi proliferate in blood vessels and penetrate cribriform plate to enter brain; causes rhinocerebral and frontal lobe ascesses, headache, facial pain, black necrotic eschar on face
Treatment: Amphotericin B
Microscopic description of mucormycosis
Biopsy shows aseptate, right-angle branching
Pneumocystosis
Etiology: Pneumocystis jiroveci
Epidemiology: Normal flora of the lungs; almost exclusively affects immunocompromised pts
Presents as pneumonia with 15% fatality
CXR shows diffuse peri-hilar infiltrates
Systemic Candidiasis - Diagnosis
Biopsy - pseudohyphae with yeast
Culture - GMS stain
Microscopic description of Blastomyces
“Broad-budding yeast”
Microscopic description of Aspergillosis
Mold with hyphae that branch at 45 degree angles with rare fruiting bodies
Microscopic description of Histoplasmosis
“Small intracellular yeast” or tiny yeasts inside macrophages
