Which of the following is a non-dimorphic fungus that is found in concentrated bird droppings and can readily cause meningitis in immunocompromised individuals?

• A. Coccidioides immitis
• B. Candida albicans
• C. Cryptococcus neoformans
• D. Histoplasma capsulatum

Answer: (C)

Bird droppings provide a reservoir for Cryptococcus neoformans, a non-dimorphic yeast that can invade the central nervous system in people with weakened cell-mediated immunity and cause meningitis. Because it stays as a yeast and does not switch to a mold form, it’s distinguished from dimorphic fungi like Histoplasma capsulatum and Coccidioides immitis, which have both mold and yeast forms depending on the environment. The organism is famously associated with soil contaminated by pigeon droppings, so exposure in that setting can lead to inhalation and subsequent CNS infection in immunocompromised individuals, such as those with AIDS. Diagnostic clues include special stains in CSF showing encapsulated yeast when using India ink, and a positive cryptococcal antigen test. The capsule, visible with mucicarmine staining, is a key feature that helps confirm the diagnosis.