Histoplasma capsulatum is a fungus found in the soil of the central and eastern United States (especially Mississippi and Ohio river valleys), eastern Canada, Mexico, Central America, and South America. The infection occurs when a person breaths in the reproducing parts of the fungus, called spores. Those with healthy immune systems usually do not have symptoms, or only mild ones. This "acute" infection does not persist. However, the infection can linger in those with lung problems such as smokers with emphysema or chronic obstructive pulmonary disease ( COPD). This condition is called "chronic" pulmonary histoplasmosis. The symptoms and chest x-ray findings of chronic pulmonary histoplasmosis are similar to tuberculosis. Risk factors for chronic pulmonary histoplasmosis include: - Living in or traveling to central or eastern United States
- Exposure to soil or particles contaminated with droppings of chickens, bats, or blackbirds
- Pre-existing COPD
- Weakened immune systems such as in people who have AIDS
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