Blastomycosis

Blastomycosis is a fungal infection caused by the organism Blastomyces dermatitidis. Endemic to portions of North America, blastomycosis causes clinical symptoms similar to histoplasmosis.

History
Blastomycosis was first described by Thomas Casper Gilchrist in 1894 and sometimes goes by the eponym Gilchrist's disease. It is also sometimes referred to as Chicago Disease.

Epidemiology
In the United States, blastomycosis is endemic in the Mississippi river and Ohio river basins and around the Great Lakes. The annual incidence is less than 1 case per 100,000 people in Mississippi, Louisiana, Kentucky, and Arkansas. The cases are greater in northern states such as Wisconsin, where from 1986 to 1995 there were 1.4 cases per 100,000 people.

In Canada, most cases of blastomycosis occur in northwestern Ontario, particularly around the Kenora, Ontario area. The moist, acidic soil in the surrounding woodland harbors the fungus.

Blastomycosis is distributed internationally; cases are sometimes reported from Africa.

Pathology
Infection occurs by inhalation of the fungus from its natural soil habitat. Once inhaled in the lungs, they multiply and may disseminate through the blood and lymphatics to other organs, including the skin, bone, genitourinary tract, and brain. The incubation period is 30 to 100 days, although infection can be asymptomatic.

Clinical features
Blastomycosis can present in one of the following ways:
 * a flulike illness with fever, chills, myalgia, headache, and a nonproductive cough which resolves within days.
 * an acute illness resembling bacterial pneumonia, with symptoms of high fever, chills, a productive cough, and pleuritic chest pain.
 * a chronic illness that mimics tuberculosis or lung cancer, with symptoms of low-grade fever, a productive cough, night sweats, and weight loss.
 * a fast, progressive, and severe disease that manifests as ARDS, with fever, shortness of breath, tachypnea, hypoxemia, and diffuse pulmonary infiltrates.
 * skin lesions, usually asymptomatic, appear as ulcerated lesions with small pustules at the margins
 * bone lytic lesions can cause bone or joint pain.
 * prostatitis may be asymptomatic or may cause pain on urinating.
 * laryngeal involvement causes hoarseness.

Diagnosis
Once suspected, the diagnosis of blastomycosis can usually be confirmed by demonstration of the characteristic broad based budding organisms in sputum or tissues by KOH prep, cytology, or histology. Tissue biopsy of skin or other organs may be required in order to diagnose extra-pulmonary disease. Commercially available urine antigen testing appears to be quite sensitive in suggesting the diagnosis in cases where the organism is not readily detected. While culture of the organism remains the definitive diagnostic standard, its slow growing nature can lead to delays in treatment of up to several weeks.

However, sometimes blood and sputum cultures may not detect blastomycosis; lung biopsy is another option, and results will be shown promptly.

Treatment
Itraconazole given orally is the treatment of choice for most forms of the disease. Cure rates are high, and the treatment over a period of months is usually well tolerated. Amphotericin B is considerably more toxic, and is usually reserved for critically ill patients and those with central nervous system disease.

Prognosis
Mortality rate in treated cases
 * 0-2% in treated cases among immunocompetent patients
 * 29% in immunocompromised patients
 * 40% in the subgroup of patients with AIDS
 * 68% in patients presenting as acute respiratory distress syndrome (ARDS)