What is the likely diagnosis for a farmer with a chronic cough and an opaque lung mass showing yeast forms on biopsy?

The chronic cough and the presence of an opaque lung mass containing yeast forms on biopsy strongly indicate histoplasmosis as the diagnosis. Histoplasmosis is caused by the fungus Histoplasma capsulatum, which is typically found in soil enriched with bird or bat droppings, making it common among farmers and those who spend time outdoors in areas where these droppings accumulate.

The chronic cough often occurs as the infection progresses, leading to respiratory symptoms that can mimic other pulmonary diseases. The identification of yeast forms on biopsy is characteristic of Histoplasma capsulatum, as this fungus presents as a small yeast in tissue specimens, particularly in cases of histoplasmosis.

In contrast to the other conditions listed, the clinical features and biological characteristics specifically align with histoplasmosis. For example, while coccidioidomycosis (caused by Coccidioides immitis) may also present with respiratory symptoms, it would typically lead to a different pattern on imaging and not have the same distinct yeast form profile as seen in histoplasmosis. Blastomycosis is associated with the fungus Blastomyces dermatitidis and may present with similar lung masses but typically does so in a different demographic and has a distinctive morphology on histopathological examination