Histoplasmosis is infection caused by the fungus Histoplasma capsulatum. It occurs mainly in the lungs but can sometimes spread throughout the body.
The spores of Histoplasma are present in the soil and are particularly common in the eastern and Midwestern United States, along the Ohio and Mississippi river valleys. Farmers and others who work with soil are most likely to inhale the spores. Severe infection can result when large numbers of spores are inhaled. People with human immunodeficiency virus (HIV) infection are more likely to develop histoplasmosis, especially the form that spreads through the bloodstream to other parts of the body, such as the liver, spleen, lymph nodes, adrenal glands, digestive system, and bone marrow.
Most people with histoplasmosis do not develop any symptoms. However, the following three forms cause symptoms, as do some rare forms.
Acute Pulmonary 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.
This form is very rarely fatal but can become serious in people with a weakened immune system (such as those with AIDS).
Progressive Disseminated Histoplasmosis:
This form does not normally affect healthy adults. It usually occurs in infants or very young children and in people with a weakened immune system. Symptoms are vague at first. People may experience fatigue, weakness, and a general feeling of illness (malaise). Symptoms may worsen very slowly or extremely rapidly. 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's disease (see see Addison Disease).
Without treatment, this form is fatal in 90% of people. Even with treatment, death may occur rapidly in people with AIDS.
Chronic Cavitary Histoplasmosis:
This lung infection develops gradually over several weeks, causing a cough and increased difficulty breathing. Symptoms include weight loss, a mild fever, and a general feeling of illness (malaise).
Most people recover without treatment within 2 to 6 months. However, breathing difficulties may gradually 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 make the diagnosis, a doctor obtains samples of the sputum, bone marrow, urine, or blood. Samples may also be taken from the liver, lymph nodes, or any mouth ulcers that are present. These samples are sent to a laboratory for culture and examination. Urine and blood may be tested for proteins (antigens) released by the fungus.
For some rare forms of the infection, the help of infectious disease specialists is required for diagnosis (and treatment).
People with acute pulmonary histoplasmosis rarely require drug treatment. However, fluconazole or itraconazole is often prescribed to shorten the duration of the illness.
People with progressive disseminated histoplasmosis need treatment and often respond well to amphotericin B given intravenously or to itraconazole (or other related drugs) given by mouth. 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 if their CD4 count (the number of one type of white blood cell) increases and stays high enough for at least 6 months.
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.
Last full review/revision October 2008 by Alan M. Sugar, MD