Histoplasmosis and Other Endemic Fungal Pneumonias

Paul C. Stillwell, MD, FAAP

Introduction/Etiology/Epidemiology

•Histoplasmosis is the most common endemic fungal infection in North America.

•The geographic distribution is primarily the Mississippi and Ohio River Valleys.

•The severity of the infection ranges from mild and often unrecognized to severe and life-threatening; immunocompromised patients are more likely to experience a severe or life-threatening infection with the endemic fungi.

•The organism Histoplasma capsulatum is found in the soil (particularly soil rich in bird and bat droppings), caves, old buildings, and chicken coops.

•Once inhaled, the spores are engulfed by macrophages, and the infection is controlled by the cell-mediated immunity.

•Because H capsulatum is an intracellular organism, it can persist for years before re-emerging if there is a deterioration of the host’s cell-mediated immune system.

•Several different manifestations of thoracic histoplasmosis have been described, with some overlap:

—Acute pulmonary histoplasmosis

—Subacute pulmonary histoplasmosis

—Chronic pulmonary histoplasmosis (uncommon in the pediatric age range)

—Disseminated histoplasmosis (immunocompromised hosts)

—Mediastinal granulomas and fibrosis

•In patients with mild acute pulmonary endemic mycosis:

—Symptoms are minimal and may include malaise, low-grade fever, and arthralgias.

—Cough and chest discomfort may be present.

—If these symptoms resolve spontaneously, medical care is usually not pursued, and the infection may go undetected.