Definition of Histoplasmosis:

Histoplasmosis is a fungal infection caused by Histoplasma capsulatum. It primarily affects the lungs but may spread to other organs.

Causes, incidence, and risk factors:

Histoplasmosis is a fungal infection that can occur almost anywhere in the world. In the United States, it is most common in the southeastern, mid-Atlantic, and central states.

The lungs are the point of entry for this infection. Histoplasma 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.

Histoplasmosis may have no symptoms. There may be a short period of active infection, or it can become chronic and spread throughout the body. Most patients with symptomatic histoplasmosis will have a flu-like syndrome and pulmonary (lung) complaints related to underlying pneumonia or other lung involvement. Individuals with chronic lung disease (e.g., emphysema, bronchiectasis) may be at higher risk of a more severe infection.

If the body responds to infection with extreme inflammation (irritation and swelling, with presence of extra immune cells in affected area), up to 10% of patients may have complications involving the skin, bones or joints, or the lining of the heart (pericardium).

In a small proportion of patients, histoplasmosis may be widespread (disseminated histoplasmosis), and involve the blood, meninges (linings of the brain), adrenal glands, and other organs. Very young or very old people, or those who have underlying immune disorders such as AIDS, are at higher risk for disseminated histoplasmosis.