Disease: Histoplasmosis

Agent: Fungal spores

Vectors: None, but grows in soil enriched by bird and bat droppings (especially pigeons)

Route: Inhalation

Symptoms: Mild, flu-like, pneumonia. Can be fatal.


Caused by: a fungus (mold)

Most common way people catch it: The only way it can be caught is through breathing in the mold spores.

Worst-case scenario: Death

How common in the Northeast? Common. The CDC estimates that 80% of people living in areas where the mold spores are common have been exposed to histoplasmosis. Most cases are mild. Causes about 800 deaths in the U.S. each year.

Most vulnerable groups: Very young or very old people, and people with compromised immune systems, because they’re more likely to develop the most dangerous form of the disease. Construction workers, NWCOs, and cavers, because they’re more likely to encounter the spores.

Histoplasmosis is a lung infection caused by inhaling the spores of the fungus, Histoplasma capsulatum. There are three forms of this disease.

Most people experience its mildest form, usually showing no symptoms or suffering a minor, flu-like illness that gets better on its own. In fact, many people are unaware they’ve been infected. The disease can develop into a chronic form that resembles tuberculosis, with the patient’s condition worsening over months or years. The most serious version, which affects the fewest people, is called “disseminated histoplasmosis.” This means the fungal infection has spread to other organs, and unless treated, it’s usually fatal.

Why do some people become so much sicker than others? It probably depends on the number of spores inhaled and the person’s age and health. Young children, long-term smokers, and elders, especially those already suffering from a lung disease, are more likely to show symptoms of histoplasmosis. People with compromised immune systems (such as those with diabetes, cancer, HIV or AIDS, and transplant recipients) are at the greatest risk for developing the most dangerous form of this infection. Histoplasmosis is one of the most frequent opportunistic infections afflicting people who are HIV-positive.

The Histoplasma fungus is common in the central and eastern U.S., especially along the Ohio, Mississippi, and St. Lawrence River Valleys and the Rio Grande. The CDC estimates that as many as 80% of the people living in these areas have been exposed to histoplasmosis. And 10–25% of those residents who are HIV-infected develop the most severe form of the infection. Overall, each year in the U.S., there are about 500,000 infections, 5,000 people hospitalized, and 800 deaths due to histoplasmosis.

How do you catch it?

You must inhale the mold spores to catch histoplasmosis. (If symptoms occur, they usually begin about 10 days after exposure.) Spores are often encountered in old or abandoned bird or bat roosts, especially those that are outside or exposed to rain; in chicken coops; and in caves. The spores are airborne. They may be inhaled when contaminated soil or droppings are disturbed.

The disease is not contagious; it’s not spread from person to person, or by other animals. Birds and bats do not carry this disease but they are associated with it because their dropping enrich soil and promote the growth of the fungus.

The fungus is naturally occurring and can grow in various soils, with or without droppings. Although it’s almost always associated with soil, the fungus has, in rare cases, been found in droppings alone. It grows readily in the soil beneath bird roosts, but it cannot form spores under the acidic conditions of fresh droppings; this means that an active roost may only give off a few spores. The droppings must dry out and then get wet before spores can be released. Generally, droppings need to accumulate for three or more years before the spores increase to significant levels underneath a roost.

If the soil is stirred up under dusty conditions, massive numbers of spores may be released. Severe epidemics have occurred in association with bird roosts that were bulldozed during construction projects. Once airborne, spores can easily be carried long distances by the wind.

Review questions
1. People catch histoplasmosis from
a. sexual contact with an infected person
b. breathing in the mold spores
c. rubbing their eyes after they’ve touched an area contaminated with bat droppings
d. cleaning the cat’s litter box
e. birds

2. Histoplasmosis is common in the Northeast. (Circle correct answer)
True or False

3. Typical hot spots for this disease include
a. caves
b. attics that are inhabited by rodents
c. old, abandoned bird or bat roosts
d. poultry barns
e. answers “a,” “b,” and “c” are correct

f. answers “a,” “c,” and “d” are correct

  • Reveal Answers


Antifungal medications are used to treat severe cases of histoplasmosis. Mild cases usually resolve themselves without treatment.

Protection on the Job:

Precautions should be taken when working around old or abandoned roost sites, especially if they’ve been exposed to rain. Avoid stirring up dust and inhaling spores. If at all possible, schedule jobs when the weather is cool and damp. Wear a proper respirator, disposable coveralls, goggles, gloves, and disposable shoe coverings. If materials are likely to fall from overhead, wear a hood.

Ventilate the area, if possible. Dampen contaminated materials to reduce the amount of dust, and keep them damp as you’re working. The droppings can be wiped up with a damp sponge. Double-bag them for disposal. Any dead birds or bats should also be sprayed with a household disinfectant, then double-bagged.

An industrial vacuum with a high-efficiency filter can also be used to clean up the site.

Advice for Homeowners:

The fungus is common in the Northeast area, so it’s smart to protect yourself before going near bird or bat droppings. If you’re concerned about exposure, avoid dusty places that might be contaminated with the mold, such as construction and demolition sites, caves, attics, and poultry barns with dirt floors.

If you develop flu-like symptoms anywhere from 3–18 days after a potential exposure to the spores, you may want to see a doctor for testing.

The best way to prevent exposure to histoplasmosis is to discourage birds and bats from roosting within buildings.

For more information about Histoplasmosis:

CDC – Disease Information – Histoplasmosis

Histoplasmosis: Protecting Workers at Risk

MEDLINEplus Medical Encyclopedia: Histoplasmosis

AIDS Education Global Information System (AEGIS)