Chapter Study Questions Hint for Question 21, Histoplasmosus capsulatum is a fungus found naturally in soils and in areas contaminated with bird and bat droppings. Most people living in areas where the fungus is endemic have contracted it through airborne spores and, after a brief period of flu-like illness (called histoplasmosis), become immune to it. However, some people develop severe lung infections; in some patients, the infection can spread to other organs. These infections can be fatal if not treated. Histoplasmosis is not transmitted from person to person. The name of each hypothesis is a good summary of the mechanism it represents.