Coccidioides species form nonbudding spherules filled with endospores; endemic to California and the southwestern United States. Which organism forms such spherules?

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

Answer: (D)

The feature being tested is the distinctive tissue form of Coccidioides species: large, nonbudding spherules filled with endospores. In the lungs, inhaled arthroconidia develop into thick-walled spherules that contain numerous endospores, a hallmark of coccidioidomycosis. This morphological pattern, along with the geographic clue—endemic to California and the southwestern United States—points to Coccidioides immitis (and its related species). Other fungi have different forms in tissue, such as Blastomyces presenting with broad-based budding yeast, Histoplasma showing small intracellular yeasts within macrophages, and Paracoccidioides with multiple budding in a “pilot wheel” arrangement.