- Histoplasmosis is disease caused by an infection with a fungus, Histoplasma capsulatum.
- The infection results from inhaling airborne spores of the fungus.
- The fungus is common in the U.S. in the Ohio and Mississippi River valleys and is often found in soil contaminated by bird or bat droppings.
- Most people who are exposed to the fungus do not develop the disease.
- The disease is most severe in people with reduced immune function.
- Symptoms of histoplasmosis are similar to those of pneumonia.
- Mild cases of histoplasmosis do not require specific treatment, and more severe or disseminated infections require antifungal medications.
- There is no vaccine available to prevent histoplasmosis.
What is histoplasmosis?
Histoplasmosis is a disease caused by an infection with a fungus known as
Histoplasma capsulatum, which is found in the environment, most frequently in
association with bird or bat droppings. The infection can cause a lung disease
similar to pneumonia in some people. In some cases, the infection spreads
throughout the body, known as disseminated disease. Disseminated histoplasmosis
is most common in people with weakened immune systems, such as those with
HIV/AIDS, those receiving cancer chemotherapy, or people taking immune-suppressant medications for chronic conditions or transplants. Spread to other
organs in immunosuppressed people may involve the liver, spleen, brain, joints,
eyes, and bone marrow.
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What are the symptoms of histoplasmosis?
Most infected persons have no apparent ill effects. The acute respiratory disease is characterized by respiratory symptoms, a general ill feeling, fever, chest pains, and a dry or nonproductive cough. Distinct patterns may be seen on a chest x-ray. Chronic lung disease resembles tuberculosis and can worsen over months or years. The disseminated form is fatal unless treated.
What causes histoplasmosis?
The causative organism is a fungus, Histoplasma capsulatum. The fungus is
often found in association with bird or bat droppings in the environment. When
the microscopic fungal spores are inhaled, some people develop an illness
similar to pneumonia. Not everyone who inhales the spores develops the illness.
The spores may become airborne in demolition projects in areas that contain bat
or bird droppings. The airborne spores can travel hundreds of feet. It has been
estimated that in the U.S. around 250,000 people are infected each year.
Histoplasma capsulatum can be found throughout the world, but it is most
commonly located in North and Central America. Within the U.S., it is particularly
common in the Ohio and Mississippi River valleys. In areas where the fungus is
common, between 50%-80% of people will show an antibody response to the
organism, meaning that they have been exposed to the fungus at some point in
What are risk factors for histoplasmosis?
Anyone may develop histoplasmosis. However, the illness is more likely to
occur in infants, young children, and the elderly. People with suppressed immune
function or chronic lung disease are also at increased risk for severe
(disseminated) disease. The soil may also become contaminated with the fungus,
so those who work with soil, such as landscapers and farmers, are at greater
risk. Also at risk are workers performing demolition work in areas that may be
contaminated with bird or bat droppings.
What are histoplasmosis symptoms and signs?
As mentioned before, not everyone who inhales the fungal spores becomes sick. When illness does occur, the signs and symptoms appear anywhere from three to 17 days after exposure. The symptoms are similar to pneumonia and include fever, chills, sweats, a dry cough, malaise, and chest pains. Some affected people also experience joint pains.
If the disease progresses without treatment, those affected may develop weight loss, shortness of breath, and fatigue. Ocular involvement in disseminated disease can cause loss of vision. If the infection spreads to the central nervous system, severe symptoms including seizures, headaches, and confusion may develop.
How do physicians diagnose histoplasmosis?
The symptoms and signs of histoplasmosis are not specific enough to establish
the diagnosis. The diagnosis rests upon demonstrating the fungus or an immune
response to the fungus. Some of the many diagnostic laboratory tests available
include the following:
- Cultures of body fluids or tissues to identify the fungus
of surface markers of Histoplasma in a urine test
- Blood tests to measure
antibody response to Histoplasma
- Microscopic examination of samples of
Chest X-rays in people with acute histoplasmosis are usually normal. However,
so-called coin lesions or histoplasmomas may be seen in the chest X-ray of
people with healed histoplasmosis. These are round accumulations of scar tissue.
Calcification of lymph nodes around the bronchi may be evidence of prior healed
infections. Depending on the severity and stage of the disease, infiltrates or
other changes may be apparent on X-rays.
CT scans are useful to identify areas of spread in disseminated
What is the treatment for histoplasmosis?
Mild cases of histoplasmosis that are limited to the lungs will resolve
without specific treatment in about a month. Severe or disseminated cases of
histoplasmosis require treatment with antifungal medications. Itraconazole (Sporanox, Onmel), fluconazole (Diflucan), and amphotericin B (Ambisome, Amphotec; drug of choice for severe disease) are
antifungal drugs that are typically used to treat histoplasmosis. Treatment may
need to be continued for a period of several months.
What is the prognosis of histoplasmosis?
People with mild symptoms of histoplasmosis usually resolve the disease on
their own without treatment. In more severe cases, the prognosis is good for
those who receive appropriate treatment. Certain people will experience
relapsing infections and may need long-term therapy with antifungal drugs.
Chronic pulmonary histoplasmosis has a mortality (death) rate of up to 50% if no
treatment is received (and 28% with treatment). Disseminated histoplasmosis has
a poor prognosis when untreated.
Is it possible to prevent histoplasmosis?
There is no vaccine against histoplasmosis. In areas where the fungus is
common, it may not be possible to prevent infection. Avoiding areas with bird
and bat droppings may provide some protection. Wearing a respirator face mask
can provide protection for workers in contaminated areas. Spraying soil with
water before working the soil may help prevent release of spores into the air.
Having had histoplasmosis in the past can offer some protection against severe
disease of you become reinfected.
Medically reviewed by Robert Cox, MD; American Board of Internal Medicine with subspecialty in Infectious Disease
Fayyaz, Jazeela. "Histoplasmosis." Medscape.com. Nov. 20, 2013.
United States. Centers for Disease Control and Prevention. "Histoplasmosis." Feb. 13, 2014.