Risky Trips: Caving, especially in the Ohio and Mississippi river valleys. In the United States, about 500,000 people are exposed to the Histoplasma capsulatum fungus each year.
Vital Signs: You can be infected with histoplasmosis when you inhale the fungus spores from soil or bat droppings (a.k.a. guano)—you might not even know that you’ve been afflicted, although some experience difficulty breathing and flu-like symptoms. Left untreated, this uncomfortable feeling could develop into anemia, meningitis and pneumonia, especially if you have a weak immune system. “When you’re caving, always wear respiratory protection, and don’t go near bats,” recommends Adalja. “They carry a slew of diseases that can kill humans.” (Plus, you wouldn’t want guano to end up in a cut—or your eyes. Gross.)