Histoplasma capsulatum, a fungal infection, causes histoplasmosis, a disease that has infected around 40 million people in the United States at some point in their lives, Thomas Volk of the University of Wisconsin-La Crosse reports. As many as 80 to 90 percent of people in the central United States test positive on skin tests for the fungus, Volk adds. About 95 percent of people have benign disease with no symptoms, but flu-like symptoms can occur around 10 days after infection. A chronic lung disease similar to tuberculosis can occur, which worsens over time.
Droppings
Histoplasmosis grows best in soil contaminated with bird or bat droppings, which have a high nitrogen content. Soil contaminated with droppings from chickens, pigeons, starlings and other blackbirds as well as bats provide a medium for spore growth. While birds and chickens themselves aren't contaminated with histoplasma capsulatum, bats can become contaminated with it and can excrete the fungus in their droppings, the Centers for Disease Control and Prevention reports.
Fungal Growth
Histoplasma capsulatum grows in soil, not in bird droppings, with the exception of bats. The droppings merely provide a good growth source. Bird droppings on a windowsill or other area aren't contaminated with the fungus, although birds can carry the fungus in soil on their feet, feathers or beaks. A moderate climate and moist soil provide the ideal environment for fungal growth, MayoClinic.com states.
Inhalation
Histoplasma capsulatum spores, called conidia, must be inhaled to cause infection. Conidia are extremely small and light and float into the air when soil is disturbed. People living or working around large numbers of birds or chickens such as farmers, gardeners, earth movers and people who work in caves are prone to develop histoplasmosis.
