American Board of Internal Medicine (ABIM) Certification Practice Exam

Histoplasma capsulatum is typically associated with which environmental factor?

1. Contaminated water sources

2. Exposure to farm animals

3. Soil contaminated with bird or bat droppings

4. High humidity levels

The correct answer is: Soil contaminated with bird or bat droppings

Histoplasma capsulatum is a dimorphic fungus that is primarily associated with environments rich in organic matter, specifically soil that is contaminated with bird or bat droppings. This particular association is significant because the droppings provide a nutrient-rich substrate that fosters the growth of the fungus. When spores of Histoplasma capsulatum are disturbed, often during activities such as digging in contaminated soil or engaging with bat caves, individuals can inhale the airborne spores, leading to potential infection. The geographic regions where this fungus is prevalent often coincide with areas where there are large populations of birds, particularly starlings, or colonies of bats. While other environmental factors listed may influence general health or exposure to pathogens, they are not specifically linked to the ecology of Histoplasma capsulatum in the same way that contaminated soil is. Understanding this association is crucial for both prevention and diagnosis of histoplasmosis, especially in endemic areas.