A recent newspaper article said that Bob Dylan, my favorite singer, was just released from the hospital after treatment for a dangerous fungal infection called histoplasmosis. I would like to know more about histoplasmosis. How does the infection start? How is it diagnosed and treated?
Infection begins when tiny spores of the histoplasmosis fungus are inhaled into the lungs. The fungus grows best on the surface of moist soils, containing bird and bat droppings. Although infection is found worldwide, in this country most cases are in the Mississippi and Ohio river valleys.
Exposure to the fungal spores can easily occur when they become airborne during such activities as raking, digging or bulldozing in infected soils, working around rotten trees or woodpiles, exploring caves or cleaning a chicken coop with a dirt floor.
The course of the infection depends in large part on the size of the exposure and the individual's immune system. When exposure is light, only about one in 100 people develops any symptoms, and they usually are mild -- cough, slight fever, like a case of the flu. With or without symptoms, most of these individuals heal completely, though a small area of calcification may be left in the lungs or the lymph nodes in the chest near the lungs (hilar lymph nodes).
In a few people, the infection may follow a more dangerous course by causing a chronic infection in the lung or disseminating widely to other tissues in the body. Chronic pneumonia and destruction of lung tissue is more common in smokers, and dissemination is more likely in those with a compromised immune system. The infection can spread to the liver, heart valves (endocarditis), the sac surrounding the heart (pericarditis), bone marrow (anemia, low blood platelets and white blood cell counts), the stomach and duodenum (ulcers), and the membranes surrounding the brain (meningitis). Unless treated, this disseminated form of histoplasmosis is fatal about 90 percent of the time.
Because histoplasmosis can mount an immune response, skin tests are often done. But mild infections long since healed are so common that the tests show evidence of exposure by age 16 in as many as 80 percent of those living in areas where the fungus commonly infests soil.
The only certain ways of diagnosing a new case are to grow the organism from infected body tissues or to show the presence of the fungus by microscopic examination of infected sites.
Disseminated histoplasmosis can be treated effectively if the diagnosis is made quickly and anti-fungal drug therapy is started early. A prolonged course of either ketoconazole or itraconazole pills is effective. In more severe cases, or when the immune system is suppressed, the treatment involves the intravenous administration of amphotericin B, usually every other day for at least 10 weeks.
Bob Dylan's histoplasmosis was complicated by pericarditis. In about 10 percent of patients with histoplasmosis, the presence of the fungus in the hilar lymph nodes, which are close to the heart, may cause pericarditis that resolves without the need for treatment with the powerful anti-fungal drugs mentioned above. Since his treatment is said to be continuing, however, it is likely
that the fungus had spread to the pericardium.
Dr. Margolis is professor of medicine and biological chemistry at the Johns Hopkins School of Medicine.