A man has difficulty breathing and a cough and is running a fever. He is an avid

The man may have histoplasmosis, caused by Histoplasma capsulatum, or cryptococcosis, caused by Cryptococcus neoformans. Both of these fungi are saprobes that grow in bird droppings. Inhaled spores germinate in the lungs and give rise to parasitic forms of the fungi.

H. capsulatum is a dimorphic true pathogen, and fungus from lung samples will revert to the hyphal form when grown at laboratory temperatures. Amphotericin B is the treatment of choice.

C. neoformans is a monomorphic yeast with a thick capsule. The presence of spherical yeast cells with thick capsules in tissue samples indicates infection with C. neoformans and can be confirmed by detecting C. neoformans antigens in the samples or serum. Treatment of cryptococcosis is usually a combination of amphotericin B and 5-fluorocytosine administered for several weeks.