Histoplasmosis is an infection caused by a fungus called Histoplasma. The fungus lives in the environment, particularly in soil that contains large amounts of bird or bat droppings. In the United States, Histoplasma mainly lives in the central and eastern states, especially areas around the Ohio and Mississippi River valleys. The fungus also lives in parts of Central and South America, Africa, Asia, and Australia. People can get histoplasmosis after breathing in the microscopic fungal spores from the air. Although most people who breathe in the spores don’t get sick, those who do may have a fever, cough, and fatigue. Many people who get histoplasmosis will get better on their own without medication, but in some people, such as those who have weakened immune systems, the infection can become severe.