Histoplasmosis and blastomycosis vs Coccidioidomycosis
How to tell Histoplasmosis and blastomycosis and Coccidioidomycosis apart when a board question makes them look alike.
Histo = macrophage intracellular Ohio/bird-bat; Blasto = broad-based Great Lakes skin/bone; Cocci = Southwest spherules with endospores.
Side by side
Histoplasma is Ohio/Mississippi River valley bat/bird droppings with intracellular yeasts in macrophages; Blastomyces is Great Lakes/Ohio-Mississippi with broad-based budding yeasts and lung/skin/bone disease.
Coccidioides is Southwest desert exposure with pneumonia, erythema nodosum, arthralgia, and spherules filled with endospores; dissemination risk rises in pregnancy and immunosuppression.
Dimorphic fungi grow as molds in environment and yeasts in tissue; inhaled spores cause pulmonary disease and possible dissemination.
Coccidioides arthroconidia are inhaled and become tissue spherules that release endospores.
Intracellular narrow-based yeasts support Histoplasma; broad-based budding yeasts support Blastomyces; antigen/serology/culture help confirm.
Spherules with endospores, desert travel, complement fixation/serology, and erythema nodosum support coccidioidomycosis.
The trap
All are dimorphic pulmonary fungi, so geography plus tissue morphology is the fastest separator.
The repair move
For endemic mycoses (dimorphic fungi: mold at 25 C in soil, yeast at 37 C in tissue), pair geography with tissue morphology: (1) HISTOPLASMA capsulatum: Ohio and Mississippi River Valleys; bat caves and bird droppings; INTRACELLULAR small yeast (2 to 4 micrometers) within macrophages on biopsy; clinical disease ranges from asymptomatic to flu-like illness to disseminated disease in immunocompromised (pancytopenia, hepatosplenomegaly, oral ulcers); treat with itraconazole for mild, amphotericin B for severe or disseminated. (2) BLASTOMYCES dermatitidis: Great Lakes states, Mississippi/Ohio Valleys, around southeastern rivers; BROAD-BASED BUDDING yeast on biopsy with thick refractile wall; pulmonary plus skin and BONE involvement (verrucous skin lesions, lytic bone lesions); treat with itraconazole or amphotericin B for severe. (3) COCCIDIOIDES immitis and posadasii: Southwest US (Arizona, California, New Mexico, Texas), Mexico, Central America; SPHERULES filled with endospores on biopsy (about 30 to 60 micrometers); 'Valley Fever' with self-limited pulmonary disease plus erythema nodosum (desert bumps) or erythema multiforme; disseminated disease in Filipinos, African Americans, pregnant women, and immunocompromised; treat with fluconazole or amphotericin B for severe. (4) PARACOCCIDIOIDES: Central and South America; CAPTAIN'S WHEEL multiple budding yeast on biopsy; treat with itraconazole.
Try a free question
CoreA spelunker in the Ohio River valley develops pneumonia and hepatosplenomegaly; biopsy shows small intracellular yeasts within macrophages. Which fungus is most likely?
Show answer and explanation
Answer: A. Histoplasma capsulatum. Ohio River valley exposure with intracellular yeasts in macrophages supports Histoplasma.
Why the other choices are tempting
- B. Blastomyces has broad-based budding yeasts.
- C. Coccidioides has spherules with endospores and Southwest desert exposure.
- D. Aspergillus has septate acute-angle branching hyphae.
- E. Mucor has broad aseptate right-angle branching hyphae.
Flashcards
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What tissue finding supports Histoplasma?
Small intracellular yeasts within macrophages support Histoplasma.
What geography supports Histoplasma?
Ohio and Mississippi River valleys with bird or bat droppings support Histoplasma.
Quick answers
What is the fastest way to tell Histoplasmosis and blastomycosis from Coccidioidomycosis?
Histo = macrophage intracellular Ohio/bird-bat; Blasto = broad-based Great Lakes skin/bone; Cocci = Southwest spherules with endospores.
What is the key clue for Histoplasmosis and blastomycosis?
Histoplasma is Ohio/Mississippi River valley bat/bird droppings with intracellular yeasts in macrophages; Blastomyces is Great Lakes/Ohio-Mississippi with broad-based budding yeasts and lung/skin/bone disease.
What is the key clue for Coccidioidomycosis?
Coccidioides is Southwest desert exposure with pneumonia, erythema nodosum, arthralgia, and spherules filled with endospores; dissemination risk rises in pregnancy and immunosuppression.
What is the common trap with Histoplasmosis and blastomycosis vs Coccidioidomycosis?
All are dimorphic pulmonary fungi, so geography plus tissue morphology is the fastest separator.