Histoplasmosis: A disease caused by the fungus Histoplasma capsulatum. Most people with histoplasmosis have no symptoms. However, histoplasma can cause acute or chronic lung disease and progressive disseminated histoplasmosis affecting a number of organs. It can be fatal if untreated.
Positive skin tests to Histoplasma occur in as many as 80% of the people living in areas where the fungus is common, such as the eastern and central United States. Infants, young children, and older persons, in particular those with chronic lung disease are at increased risk for severe disease. Disseminated disease is more frequently seen in people with cancer or AIDS.
The fungus grows in soil and material contaminated with bat or bird droppings. Spores become airborne when contaminated soil is disturbed. Breathing the spores causes infection. The disease is not transmitted from an infected person to someone else.
Symptoms start within 3 to 17 days after exposure; the average is 10 days. The acute respiratory disease is characterized by respiratory symptoms, a general ill feeling, fever, chest pains, and a dry or nonproductive cough. Distinct patterns may be seen on a chest x-ray. Chronic lung disease resembles tuberculosis and can worsen over months or years. The disseminated form is fatal, unless treated.
Mild cases resolve without treatment. Severe cases of acute histoplasmosis and all cases of chronic and disseminated disease are treated with antifungal medications, usually for life in those with compromised immune systems.