Blastomycosis is a fungal infection caused by the organism Blastomyces dermatitidis

History

It was first described by Thomas Casper Gilchrist [1] in 1894 and sometimes goes by the eponym Gilchrist's disease [2]. It is also sometimes referred to as Chicago Disease.

Epidemiology

In the US:

• Most cases of blastomycosis occur in the United States. It 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, Kentucky, Arkansas, and Wisconsin.

In Canada:

• Most cases of blastomycosis in Canada occur in northwestern Ontario, in particular, around the Kenora area. The moist, acidic soil in the surrounding woodland harbours the fungus.

Internationally:

• Blastomycosis is distributed throughout the world. Cases are sometimes reported from Africa.

Pathophysiology

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.

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 is confirmed by demonstration of the organism, usually in the sputum, by KOH prep, culture or DNA antibody test. Organisms can also be found in skin ulcers along the margins.

Treatment

Amphotericin B is the treatment of choice, is highly effective, but is quite toxic. In milder cases, itraconazole can be used.

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)

External resources

NIH Encyclopedia Blastomycosispt:Blastomicose