HISTOPLASMOSIS

Histoplasmosis is an infection caused by Histoplasma capsulatum, a fungus that thrives in soil contaminated by certain bird and bat droppings. In the U.S., H. capsulatum is found most often along the Ohio and Mississippi River valleys as well as in other central, southeastern and mid-Atlantic states.

In those areas where H. capsulatum is prevalent, 80 percent or more of the population has been exposed to infection through breathing in airborne spores produced by the fungus. The initial infection often occurs without causing symptoms, and a healthy person usually will not develop subsequent disease.

However, people with severely damaged immune systems, such as people with AIDS, are vulnerable to a very serious disease known as progressive, disseminated histoplasmosis. This can be caused by an initial exposure to the fungus or a reactivation of a previous infection. Nationwide, about 5 percent of people with AIDS have histoplasmosis, but in geographic areas where the fungus is common, people with AIDS are at high risk for disseminated histoplasmosis.

Symptoms and Diagnosis

Histoplasmosis occurs most often in the lungs, though occasionally it affects the skin and gastrointestinal tract; the central nervous system also can be involved. The most common symptoms of disseminated histoplasmosis are fever and weight loss. Other symptoms include skin lesions, difficulty breathing, anemia (low numbers of red blood cells) and swollen lymph nodes. Unusual manifestations of disseminated histoplasmosis that occur in people with AIDS include eye and brain inflammation.

Blood, lung fluid and urine tests can be used to detect the fungus. Chest x-ray abnormalities appear in about half of people with disseminated histoplasmosis. Sometimes, samples of tissue from the lung, bone marrow or lymph nodes reveal evidence of infection.

Treatment

Acute. The antifungal drug amphotericin B is often used to treat people with histoplasmosis. Amphotericin B has many side effects including kidney damage, high fever, low blood pressure, decreased numbers of red or white blood cells, nausea, vomiting and chills. Another antifungal drug, itraconazole, also may be used for initial treatment and is usually very well tolerated. A newer formulation of amphotericin B, in which the active compound is encased in a fatty substance, is under study and may have fewer side effects.

Maintenance. Once the acute episode has been treated, doctors often recommend daily maintenance therapy with itracona- zole or fluconazole to prevent the disease from returning.

Prevention. Studies are underway to determine if AIDS patients who live in high-risk areas would benefit from pre- ventive therapy with itraconazole.

Research

The National Institute of Allergy and Infectious Diseases (NIAID) funds research aimed at finding new drugs or drug combinations for the treatment or prevention of fungal diseases, as well as better ways to administer currently available drugs. For information about clinical studies, call the AIDS Clinical Trials Information Service:

1-800-TRIALS-A
1-800-243-7012 (TDD/Deaf Access)

For federally approved treatment guidelines on HIV/AIDS, call the HIV/AIDS Treatment Information Service:

1-800-HIV-0440
1-800-243-7012 (TDD/Deaf Access)

NIAID, a component of the National Institutes of Health, supports research on AIDS, tuberculosis and other infectious diseases as well as allergies and immunology. NIH is an agency of the U.S. Public Health Service, U.S. Department of Health and Human Services.

Source:
Office of Communications
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892

Public Health Service
U.S. Department of Health and Human Services
November 1994