Which organism is a dimorphic fungus that forms yeast at body temperature and mold in the environment, commonly causing granulomatous disease?

Which organism is a dimorphic fungus that forms yeast at body temperature and mold in the environment, commonly causing granulomatous disease?

• A. Histoplasma capsulatum
• B. Blastomyces dermatitidis
• C. Coccidioides immitis
• D. Paracoccidioides brasiliensis

Answer: (A)

Dimorphism with tissue form as yeast at body temperature and environmental mold is the hallmark here, and the organism most classically linked to granulomatous lung disease is Histoplasma capsulatum. Inhaled microconidia from soil—often rich in bird or bat droppings—are taken up by alveolar macrophages and convert to small yeast within those cells. This intracellular yeast within macrophages drives the granulomatous inflammatory response, producing the lung lesions that can calcify and form granulomas, and it can disseminate in people with weakened immunity. Other dimorphic fungi can cause granulomatous disease too, but their tissue forms differ and so do their classic clues. Blastomyces dermatitidis forms larger yeasts with broad-based budding; Coccidioides immitis forms large spherules filled with endospores rather than budding yeasts; Paracoccidioides brasiliensis shows multiple budding yeast reminiscent of a pilot’s wheel. These distinctions help in identifying the specific organism, but the description given most closely aligns with Histoplasma capsulatum.

Dimorphism with tissue form as yeast at body temperature and environmental mold is the hallmark here, and the organism most classically linked to granulomatous lung disease is Histoplasma capsulatum. Inhaled microconidia from soil—often rich in bird or bat droppings—are taken up by alveolar macrophages and convert to small yeast within those cells. This intracellular yeast within macrophages drives the granulomatous inflammatory response, producing the lung lesions that can calcify and form granulomas, and it can disseminate in people with weakened immunity.

Other dimorphic fungi can cause granulomatous disease too, but their tissue forms differ and so do their classic clues. Blastomyces dermatitidis forms larger yeasts with broad-based budding; Coccidioides immitis forms large spherules filled with endospores rather than budding yeasts; Paracoccidioides brasiliensis shows multiple budding yeast reminiscent of a pilot’s wheel. These distinctions help in identifying the specific organism, but the description given most closely aligns with Histoplasma capsulatum.