What is histoplasmosis?

Histoplasmosis is an infection caused by a fungus, Histoplasma capsulatum. The principal habitat for this fungus is soil enriched by bird droppings and in bat droppings. In the United States, the fungus is found most often along the Mississippi and Ohio river valleys, but also is present in other central, southeastern and mid-Atlantic states. In people, this uncommon disease affects the lungs and may occasionally invade other parts of the body. Dogs, cats, rats, skunks, opossum, foxes and other animals also can get histoplasmosis.

Who gets histoplasmosis?

Anyone can get histoplasmosis. In some areas where the fungus is prevalent, 80 percent or more of the population has been exposed to infection through breathing in airborne spores. The initial infection often occurs without causing symptoms, and most persons usually will not develop subsequent disease, unless the exposure was heavy.

Long-term smokers and those with preexisting lung disease may be at higher risk for developing the disease.

People with severely damaged immune systems — such as those with AIDS or leukemia, those who are on corticosteroid therapy and recent transplant recipients — are vulnerable to a very serious disease known as progressive, disseminated histoplasmosis. Nationwide, about 5 percent of people with AIDS will develop histoplasmosis. In geographic areas where the fungus is common, people with AIDS are at higher risk for disseminated histoplasmosis.

How is the fungus spread?

The organism is found throughout the world and grows in soil that has been enriched with bat or bird droppings or in bat droppings themselves, for example, around old chicken houses, in caves and other areas harboring bats, and around starling and blackbird roosts. The fungus produces spores that can become airborne if the soil is disturbed. Inhalation of these spores may cause infection. The disease is not acquired through person-to-person transmission, nor is it acquired from animals that have the disease.

What are the symptoms of histoplasmosis?

The majority of infected persons have no symptoms. When symptoms occur, they vary widely, depending on the form of disease. The acute pulmonary form of the disease is a "flu"- like illness characterized by respiratory symptoms, general malaise, fever, chest pains, and a dry or nonproductive cough. Distinct patterns are seen on chest X-rays. Chronic pulmonary disease resembles chronic tuberculosis and progresses over months or years. The disseminated form of histoplasmosis is usually fatal unless treated.

How soon after exposure do symptoms appear?

If symptoms occur, they will usually appear within three to 17 days after exposure; the average is 10 days. However, disease onset could occur sooner if exposure is heavy. Most people do not experience symptoms.

Does past infection with histoplasmosis make a person immune?

Infection usually results in increased resistance to infection, but the immunity may not be complete.

How is histoplasmosis treated?

Specific antifungal medications are used to treat severe cases of acute histoplasmosis and all cases of chronic and disseminated disease. Mild disease usually resolves without treatment.

What can be done to prevent the spread of histoplasmosis?

The following steps can be taken to minimize exposure to Histoplasma capsulatum:

• Avoid areas that may harbor the fungus, particularly those areas with accumulations of bird or bat droppings.
• Minimize exposure to dust by spraying with a mist of water before working in potentially contaminated sites.
• When working in high-risk areas, all persons should wear disposable clothing and a face mask capable of filtering out particulate matter above 1 millimicron in diameter. (For more information, see Lenhart, S. W. etal., Histoplasmosis, Protecting Workers at Risk, U.S. Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, September 1997.)