DefinitionHistoplasmosis is an infection due to the Histoplasma capsulatum fungus.Alternative NamesOhio River Valley feverCauses, incidence, and risk factorsHistoplasmosis is a fungal infection. It occurs throughout the world. In the United States, it is most common in the southeastern, mid-Atlantic, and central states.The infection enters the body through the lungs. Histoplasma fungus grows as a mold in the soil, and infection results from breathing in airborne particles. Soil contaminated with bird or bat droppings may have a higher concentration of histoplasma.There may be a short period of active infection, or it can become chronic and spread throughout the body.Histoplasmosis may have no symptoms. Most people who do develop symptoms will have a flu-like syndrome and lung (pulmonary) c