Histoplasmosis is a lung infection caused by the fungus Histoplasma capsulatum. Spores of the fungus are found in bird and bat droppings and usually cause the disease by being inhaled. The fungus is found around the world and is common in the Eastern and Central U.S.; as much as 80% of the people living in these areas have been exposed to the fungus. The disease can vary in severity and symptoms start an average of 10 days after exposure.
The milder version is primary pulmonary histoplasmosis; this is a type of pneumonia and resembles a cold or flu (fever, cough, chills, etc.) Very mild cases clear up on their own and need no treatment. Amphotericin B is given to patients whose infections are acute or persist.
A somewhat uncommon variation of the primary type involves the fungus growing into a tumorlike mass in a person's lungs; this mass must usually be removed surgically.
The severe form is disseminated histoplasmosis; the infection spreads from the lungs to other parts of the body, notably the liver and spleen, and causes skin and mucous membrane lesions (most often mouth ulcers). The disease can overwhelm a person's immune system and cause lowered white blood cell counts (leukopenia). The stress of trying to fight off the infection can cause anemia.
Disseminated histoplasmosis most commonly occurs in people with immune system disorders such as AIDS, and it is fatal unless it is treated with antifungal medications such as amphotericin B or itraconazole. People who have otherwise healthy immune systems can also be given ketoconazole.
Some people who have been exposed to the dust can get an eye infection that causes inflammation and scarring on the retina. Some people with ocular histoplasmosis experience no symptoms, but others have blind spots and blurred vision. Laser surgery may be necessary to correct the scarring.
The best way to avoid histoplasmosis is to avoid breathing dust where birds have been. People who are cleaning old houses or exploring caves etc. should wear filter masks.
References: http://www.cdc.gov/ncidod/dbmd/diseaseinfo/histoplasmosis_g.htm and http://www.stlukeseye.com/Conditions/Histoplasmosis.asp.