H. capsulatum, a dimorphic fungus, is found in soil heavily contaminated with bird droppings. Which of the following statements best describes the presence of the organism in tissue biopsies?: (A) Yeasts with broad-based bud, (B) Single-cell yeasts with pseudohyphae, (C) Arthrospores, (D) Oval budding yeasts inside macrophages
Answer is D. Histoplasma capsulatum is a dimorphic fungus that forms two types of spores: tuberculate macroconidia and microconidia. Inhalation of the microconidia transmits infection. Inhaled spores (microconidia) are engulfed by macrophages and develop into yeast forms. Most infections remain asymptomatic; small granulomatous foci heal by calcification. However, pneumonia can occur. The heterophile antibody test is useful for early diagnosis of infectious mononucleosis. The figure below illustrates the oval budding yeasts.