The given clinical history and the presence of tiny yeast forms within macrophages are suggestive of Histoplasmosis which is also called Darling&;s disease. Histoplasmosis: It is also known as Darling&;s disease, Cave&;s disease, OHIO disease. The causative agent is Histoplasma capsulatum, a dimorphic fungus. Transmission occurs inhalation of conidia. After inhalation, the conidia develop into yeast cells and are engulfed by alveolar macrophages. Within macrophages, the yeasts may disseminate to reticuloendothelial tissues, such as the liver, spleen, bone marrow, and lymph nodes. Biopsy reveals tiny (2-4microns) oval-shaped yeast cells inside macrophages. On culture and microscopy, tuberculate macroconidia and hyaline septate mold with microconidia are seen Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition