How People Get Histoplasmosis

Key points

  • Histoplasmosis is a lung infection caused by breathing in spores from the fungus, Histoplasma.
  • Histoplasma lives in soil in certain parts of the U.S. and the world.
  • It cannot spread between people or between people and pets.
  • Outbreaks of histoplasmosis are rare and do not cause many cases.
bird on branch, bat flying

How it spreads

People can get histoplasmosis by breathing in spores from the fungus, Histoplasma. The fungus is typically found in soil and bird or bat droppings in certain areas of the United States and the world.

Histoplasma spores are released in the air after contaminated soil is disturbed. The spores are too small to see without a microscope. When people breathe in the spores, they are at risk for developing histoplasmosis. After the spores enter the lungs, the person's body temperature allows the spores to transform into yeast. The yeast can then travel to lymph nodes and can spread to other parts of the body through the bloodstream.

Biology of histoplasmosis

Image of the life cycle ofHistoplasma capsulatumcapsulatum: Environmental Form, Host-associated Form, and Areas of Endemicity for Histoplasmosis
Inhaled mold spores from Histoplasma turn into yeast in the lungs.

See PDF version histoplasmosis life cycle.

Histoplasmosis outbreaks

United States map showing histoplasmosis outbreak locations
Locations of 105 outbreaks and related case counts by state, 1938-2013

Outbreaks of histoplasmosis are not common. Of the few that have been reported, most occurred after events that disturb soil contaminated with bird or bat droppings. From 1938–2013, there were 105 reported outbreaks of histoplasmosis. The number of outbreak-related cases are reported by state or territorial health departments.

Some of these outbreaks happened in places where scientists did not expect Histoplasma to live. Investigating histoplasmosis outbreaks helps public health officials understand:

  • Where the fungus lives.
  • Activities that may make someone more likely to get histoplasmosis.
  • Groups of people more likely to get histoplasmosis.