Histoplasmosis is acquired by inhaling spores of the fungus.
Most people do not have symptoms, but some feel sick and have a fever and cough, sometimes with difficulty breathing.
Sometimes the infection spreads, causing the liver, spleen, and lymph nodes to enlarge and damaging other organs.
The diagnosis is based on culture and examination of tissue and fluid samples.
Whether treatment with antifungal drugs is needed depends on the severity of the infection.
(See also Overview of Fungal Infections.)
Histoplasmosis is particularly common in the eastern and midwestern United States, particularly along the Ohio and Mississippi river valley. It may occur in the Southern states. Histoplasmosis also occurs in parts of Central and South America, Africa, Asia, and Australia. Outbreaks associated with bat caves have occurred worldwide and in the United States have been reported in Florida, Texas, and Puerto Rico.
Histoplasma grows best in soil and dust that are contaminated with bird or bat droppings. Chicken farmers, construction workers, cavers (people who like to explore caves), and others who work with soil are most likely to inhale the spores produced by Histoplasma. The risk of infection is greatest when activity generates airborne spores (for example, tree or building removal at construction sites in areas where birds or bats live) or when exploring caves.
Severe illness can result when large numbers of spores are inhaled.
There are three main forms of histoplasmosis:
Acute pulmonary histoplasmosis: This form is the initial form of the infection. It occurs in the lungs and usually remains there.
Progressive disseminated histoplasmosis: If the immune system is weakened or is immature, the infection may spread (disseminate) from the lungs through the bloodstream to other parts of the body, such as the brain, spinal cord, liver, spleen, lymph nodes, adrenal glands, digestive system, or bone marrow. This form rarely occurs in healthy adults. It usually occurs in malnourished infants or very young children or in people with a weakened immune system, such as those who have HIV/AIDS, an organ transplant, or who are taking drugs that suppress the immune system, including corticosteroids.
Chronic cavitary histoplasmosis: In this form, one or more spaces (cavities) form in the lungs gradually, over several weeks. The infection does not spread from the lungs to other parts of the body.
Most people infected with Histoplasma do not develop any symptoms, or they develop only very mild symptoms.
Symptoms vary, depending on the form of histoplasmosis.
Symptoms usually appear 3 to 21 days after people inhale the spores. People may feel sick, have a fever and a cough, and feel as though they have the flu. Symptoms usually disappear without treatment in 2 weeks and rarely last longer than 6 weeks.
People who inhale many spores may develop pneumonia. They may become very short of breath and be ill for months.
Acute pulmonary histoplasmosis is very rarely fatal but can become serious in people with a weakened immune system (such as those with AIDS).
Symptoms are vague at first. People may feel tired, weak, and generally ill. Symptoms may worsen very slowly or extremely rapidly.
Pneumonia may develop but is rarely severe, except in people with AIDS. Rarely, meningitis (inflammation of the tissues covering the brain and spinal cord) may develop, causing a headache and a stiff neck. The liver, spleen, and lymph nodes may enlarge. Less commonly, the infection causes ulcers to form in the mouth and intestines. Rarely, the adrenal glands are damaged, causing Addison disease.
Without treatment, this form is fatal in more than 90% of people. Even with treatment, death may occur rapidly in people with AIDS.
This lung infection develops gradually over several weeks, causing a cough and difficulty breathing that become increasingly worse. Symptoms include weight loss, night sweats, a mild fever, and a general feeling of illness (malaise).
Most people recover without treatment within 2 to 6 months. However, breathing difficulties may continue to worsen, and some people cough up blood, sometimes in large amounts. Lung tissue is destroyed, and scar tissue forms. Lung damage or bacterial invasion of the lungs may eventually cause death.
To diagnose histoplasmosis, doctors obtain samples of the sputum, urine, blood, or mouth ulcers (if present). Doctors may use a viewing tube (bronchoscope) to take samples from the lungs. Or they may do a biopsy to take samples from the liver, bone marrow, or lymph nodes. These samples are sent to a laboratory for culture and examination. Urine and blood may be tested for proteins (antigens) released by the fungus. A test to identify the fungus' genetic material (its DNA) may be done.
Doctors also take a chest x-ray to look for evidence of lung infection.
For some rare forms of the infection, the help of infectious disease specialists is required for diagnosis (and treatment).
Acute pulmonary histoplasmosis in otherwise healthy people rarely requires drug treatment. However, if people do not improve after a month, itraconazole, given by mouth, is often prescribed. If severe pneumonia develops, people are given amphotericin B intravenously, followed by itraconazole.
Progressive disseminated histoplasmosis requires treatment. If the infection is severe, amphotericin B is given intravenously, followed by itraconazole, given by mouth. If the infection is mild, itraconazole is used alone.
If people with AIDS develop histoplasmosis, they may need to take an antifungal drug, usually itraconazole, for the rest of their life. However, they may be able to stop the antifungal drug treatment after 1 year if their CD4 count (the number of one type of white blood cell that decrease when AIDS is uncontrolled) increases to 150 or more cells per microliter of blood.
In chronic cavitary histoplasmosis, itraconazole or, for more serious infections, amphotericin B may eliminate the fungus. However, treatment cannot reverse the destruction caused by the infection. Thus, most people continue to have breathing problems, similar to those caused by chronic obstructive pulmonary disease. Therefore, treatment should begin as soon as possible to limit lung damage.