Fungal and Protozoal Diseases of the Respiratory System

Histoplasmosis. Histoplasmosis is a fungal disease caused by the yeast Histoplasma capsulatum. In the body, the infection is similar to tuberculosis, especially in immunocompromised individuals. In severe cases, it may be a progressive disease that spreads to the other organs. Most cases are associated with bird and bat droppings. Amphotericin B is useful for therapy.

Blastomycosis. Blastomycosis is due to Blastomyces dermatitidis, a yeastlike fungus. The disease is found in regions of the Mississippi Valley and is spread in dust. Tuberculosislike lesions of the lung occur, and spread to other organs is possible. Amphotericin B is used for therapy.

Coccidioidomycosis. Coccidioidomycosis is due to Coccidioides immitis, a fungus found in the soil of the southwest United States. The disease is particularly prevalent in the San Joaquin Valley of California and is sometimes called valley fever. It is transmitted in dust, and its symptoms include fever, coughing, and general malaise. Progressive disease sometimes occurs. Farm workers are particularly disposed to the disease. Amphotericin B is used for therapy.

Aspergillosis. Aspergillosis is caused by Aspergillus fumigatus, a fungus. The fungus grows in the lung tissues and forms a compact ball of fungal mycelium, which blocks the respiratory passageways. Surgery is often needed to remove the mass of fungi.

Pneumocystis pneumonia. Pneumocystis pneumonia is caused by Pneumocystis carinii. Although the organism is usually considered a protozoan, there is biochemical evidence that it may be a fungus. Pneumocystis pneumonia is associated with AIDS patients. The organisms grow in the lungs of immunocompromised individuals and cause severe consolidation, which may lead to death. A drug called pentamidine isethionate is valuable for therapy. Approximately half of the deaths associated with AIDS are due to Pneumocystis pneumonia. Pneumocystis carinii is a very complex organism with a life cycle involving mature cysts and highly resistant forms. It is present in the lungs of most individuals but does not invade the tissues unless the immune system has been compromised.