Fungi Flashcards
Geographic distribution in midwest and central US along Mississippi and Ohio river valleys
Histoplasma capsulatum
Transmission and pathogenesis of histoplasma capsulatum
Exposure to bird or bat droppings
Spores in droppings are inhaled then ingested by macrophages
Diagnosis of Histoplasma capsulatum
Histologically presents with macrophages containing intracellular oval bodies with KOH prep
Note that histoplasma is smaller than RBCs — macrophages contain many of these oval bodies
Could also use serum or urine Ag test
Clinical presentation of Histoplasma in healthy vs. immunocompromised individuals
Healthy usually asymptomatic but can present with pneumonia and granuloma formation that may calcify and mimic Tb infection. May also see erythema nodosum - painful red lesions on shins
In immunocompromised may lead to HSM because it targets reticuloendothelial system macrophages and there are many in liver and spleen (this is disseminated infection)
The systemic mycoses are considered dimorphic. What are the systemic mycoses?
Histoplasma capsulatum
Blastomyces dermatidis
Coccidoides immitis
Paracoccidioides brasiliensis
The systemic mycoses are considered dimorphic. What does this mean? What is the exception?
Dimorphic - exists in 2 forms based on environment. “Mold in the cold (external, soil), Yeast in the heat (body/lungs)”
Exception is Coccidioides immitis which dimorphic. It exists as a mold in the cold but forms spherules filled with endospores in the lungs
Geographic distribution in Great Lakes and Ohio river valley
Blastomyces dermatidis
Transmission and pathogenesis of blastomyces dermatidis
Inhalation of aerosolized spores —> replication by broad based budding (seen on KOH prep)
Dx and clinical features of blastomycoses infection
Broad-based budding yeast seen on KOH prep
Yeasts are same size as RBCs on blood smear; can also be dx by urine Ag test
CXR shows patchy alveolar infiltrate
Most are asymptomatic but may see disseminated infxn in immunocompromised, which affects skin and bone (osteomyelitis)
Geographic distribution in California and Southwestern US
Coccidioides immitis
How does one usually come into contact with coccidioides immitis? What events tend to increase incidence in endemic regions?
Inhalation of spores in dust
Dust storms and/or earthquakes cause increase in incidence
Coccidioides mycoses can cause systemic infections; they are dimorphic organisms that exist as mold in the cold and form spherules filled with endospores in the lungs of humans. How do these spherules compare to RBCs under the microscope?
Spherules are larger than RBCs
Clinical features of Coccidioides immitis in healthy people
Usually asymptomatic in healthy people but can cause self-limiting PNA with fever, cough, and arthralgia
CXR may show nothing, or cavities and/or nodules
Can also see erythema nodosum (note that this is more common in coccidioides than histoplasma) - this represents robust immune response - so it is only really seen in healthy people
Clinical features of Coccidioides immitis in immunocompromised
Skin and lung manifestations
Dissemination to bone and meninges (meningitis)
Dx of coccidioides immitis
KOH, culture, or blood culture with IgM to coccidioides
Geographic distribution in South America (often Brazil)
Paracoccidioides brasiliensis
Characteristic features of Paracoccidioides brasiliensis
Dimorphic
Yeast form looks like “captains wheel” in lungs, and is larger than RBC
Pathogenesis and clinical features of Paracoccidioides brasiliensis
Inhalation —> dissemination —> LAD —> spread to lungs causing granulomas; also see mucocutaneous lesions - often in mouth
What are the cutaneous mycoses?
Malassezia furfur
Dermatophytes (epidermophytan, trichophytan, microsporum)
Sporothrix schenckii
What primary condition is caused by Malassezia furfur?
where does this organism thrive?
Pityriasis versicolor = hyper and/or hypopigmented patches on skin
Organism thrives in hot and humid conditions
Describe appearance of Malassezia furfur on KOH prep of skin scrapings
What layer of the skin is typically affected?
“Spaghetti and meatball” appearance
Typically remains confined to stratum corneum layer of epithelium
MOA of Malassezia furfur
Produces melanocyte damaging acids via lipid degradation
Malassezia furfur typically remains confined to the skin except in what patient population?
May cause disseminated infection in neonates on total parenteral nutrition (TPN) causing thrombocytopenia and sepsis
Clinical manifestations of dermatophytes (epidermophytan, trichophytan, microsporum)
Tinea rashes (“ring-worm”) = pruritic!
Tinea capitis affects the head
Tinea corporis affects the body
Tinea cruris = jock itch
Tinea pedis = athletes foot
can also cause onychomycosis = infection of the nails
Dermatophytes often affect athletes, or they can come from animals like dogs. How are these infections diagnosed?
Typically based on H&P
Can see hyphae on KOH prep
Woods lamp used to diagnose microsporum
Rose-gardener’s disease often transmitted by scratches from rose bush or other physical trauma with dimorphic branching hyphae at 25 C
Sporotrichosis - caused by Sporothrix schenckii
Diagnosis and clinical features of sporotrichosis (sporothrix schenckii)
Dx by culture (gold standard) OR biopsy showing granulomas OR microscopy showing cigar shaped budding yeasts
Clinical presentation: ulcer at the site of initial trauma —> ascending infection via lymphatics
Describe the dimorphic character of candida albicans
Dimorphic with pseudohyphae (yeast) at 20 C, and germ-tube hyphae (mold) at 37 C
[so it is opposite the usual dimorphic pattern — this is yeast in the cold and mold in the heat!]
What about candida albicans makes it a risk for patients with CGD?
It is catalase+
Candida albicans is part of the normal flora in most people, and does not typically cause infection in healthy individuals. What are some clinical findings when it does cause infection?
Diaper rash in characteristic pattern d/t heat and humidity in diaper region
Oral candidiasis in immunocompromised or oral steroid users
Candidal esophagitis (AIDS-defining illness with CD4<100)
Vaginal candidiasis
Candidal endocarditis (IV drug users, commonly affects tricuspid)
What patient populations have increased risk of candidal vulvovaginitis?
How is vaginal candidiasis differentiated from gardnerella infection?
Increased risk in diabetics and women taking oral contraceptives
differentiated from gardnerella because candida does NOT alter vaginal pH
Besides candida albicans, what other fungus is catalase+?
Aspergillus fumigatus
How is aspergillus associated with hepatocellular carcinoma?
Peanuts and grain crops are associated with aflatoxins produced by aspergillus flavus; these aflatoxins are carcinogenic for hepatocellular carcinoma
Describe the morphology of aspergillus flavus and how this differs from mucor
Acute angle branching+septations; forms conidiophores with fruiting bodies
Mucor does not septate and has wide-angle (90 degree) branching compared to aspergillus
Transmission of aspergillus fumigatus occurs via inhalation. What are the 3 disease manifestations?
- Allergic bronchopulmonary aspergillosus (ABPA)
- Aspergillomas
- Angioinvasive aspergillosis
Describe allergic bronchopulmonary aspergillosis (ABPA)
Type 1 HSR with wheezing, fever, and migratory pulmonary infiltrate
Blood work shows increased IgE
Describe aspergillomas caused by aspergillus fumigatus infxn
Forms balls of fungus in lungs that are gravity dependent, so they show up at the bottom of a CXR
Formation of these fungal lesions is associated with prior Tb infection which created cavities
Describe angioinvasive aspergillosis
Occurs in immunocompromised, particularly in leukemia and lymphoma pts
Aspergillus invades blood vessels and disseminates through the body, leading to kidney failure, endocarditis, and ring-enhancing lesions in the brain on CT
It can also spread to the paranasal sinuses, causing necrosis around the nose (this also occurs in mucor so it is not diagnostic of aspergillus!)
Describe morphology of cryptococcus neoformans and where it is found
Heavily encapsulated (contains repeating polysaccharide capsular Ags) as main virulence factor — antiphagocytic
Urease+
Found in soil and pigeon droppings
Clinical features of cryptococcus neoformans infection
Opportunistic infection often affecting HIV pts
Causes cryptococcal pneumonia with fever, cough, and dyspnea (or may be asymptomatic)
Can also spread to the meninges, and is the MCC of fungal meningitis
What characteristics are indicative of cryptococcus neoformans infection on imaging in someone with cryptococcal meningitis?
“Soap bubble” lesions in gray matter of brain
Besides imaging, how is a cryptococcal neoformans infection diagnosed?
Bronchopulmonary washing then stained with red or silver
Lumbar puncture + India Ink stain showing 1-10 micrometers of yeast with “halos”
Latex aggluttination test detects repeating polysaccharide Ag —> agglutination is + testq
What fungi are associatiated with opportunistic fungal infections?
Candida albicans Aspergillus fumigatus Cryptococcus neoformans Mucormycetes Pneumocystis jiroveci
What patients are at high risk for mucormycetes (mucor spp, rhizopus spp.) infections?
Immunocompromised (often those with leukemia, neutropenia)
Diabetics (most common predisposing factor is DKA)
What is rhizopus?
Bread mold; Type of mucormycetes
Describe morphology of mucormycetes and how it is different from aspergillus
Hyphae are non-septate and wide-angle branching (~90 degrees)
[aspergillus are septated and acute angle branching]
Pathogenesis of Mucor infection
Spore inhalation —> proliferation in blood vessels —> invasion through cribriform plate —> necrosis of tissues
Tissue necrosis eventually leads to rhinocerebromucomycoses and frontal cortex abscesses
Black eschar forms on face and nasal cavity, indicated deep penetration into brain which may manifest as neurodisturbances and death
Transmission and clinical features of pneumocystis jiroveci
Respiratory transmission
Asymptomatic in healthy people
In immunocompromised — Diffuse interstitial pneumonia with NON-productive cough and NO lung consolidations on CXR. However, may see “ground glass” or “crushed ping pong ball” appearance on CXR
If pneumocystis pneumonia is suspected based on “ground glass” appearance on chest X-ray, how would you confirm the dx?
Bronchoalveolar lavage (BAL) then stain wtih methamine silver stain — will see ovoid/disc-shaped yeast
Could also do lung biopsy but that is more invasive
