Fungi Flashcards Preview

MOD II Exam II > Fungi > Flashcards

Flashcards in Fungi Deck (49)
Loading 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


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)