Histoplasmosis is an infection caused by breathing in spores of a fungus often found in bird and bat droppings. Histoplasmosis is most commonly transmitted when these spores become airborne, often during cleanup or demolition projects.

Soil contaminated by bird or bat droppings also can transmit histoplasmosis, so farmers and landscapers are at a higher risk of contracting the disease. In the United States, histoplasmosis commonly occurs in the Mississippi and Ohio river valleys, though it can occur in other areas, too.

Occasionally, other organs are affected; this is called disseminated histoplasmosis, and it can be fatal if left untreated.

In some people, histoplasmosis can also produce joint pain and a rash. People who have an underlying lung disease, such as emphysema, may develop a chronic form of histoplasmosis.