Blastomycosis, caused by Blastomyces dermatitidis, is principally a pulmonary infection that involves the skin after rare dissemination. Even more rarely, skin lesions follow percutaneous inoculation of the pathogen. Synonyms include North American
blastomycosis, Gilchrist's disease, Chicago disease, Namekagon fever, and blastomycetic dermatitis. The epidemiology of blastomycosis is poorly defined because clusters of human disease rarely occur. One third of foresters in northern Wisconsin and Minnesota have serologic evidence of prior infection. Sporadic disease affects mostly men, reflecting
occupational exposures, but epidemic disease affects the sexes equally. Although the disease is not considered contagious, women have acquired endometrial blastomycosis after sexual contact with partners who had genitourinary disease. In North America, other mammals, most notably dogs, naturally acquire blastomycosis. The geographical range of canine blastomycosis parallels that of human disease.
Blastomycosis is principally a North American disease, endemic in the southeastern United States (particularly Kentucky, Mississippi, and Arkansas), the Great Lakes region, and the drainage basins of the Mississippi and St. Lawrence rivers.
SYMPTOMS
Clinical Manifestations
There are three clinical forms of disease: primary
pulmonary blastomycosis, systemic blastomycosis,
and primary cutaneous inoculation blastomycosis
. The first form is the most common.
Primary Pulmonary Blastomycosis.
Primary
pulmonary blastomycosis starts with the inhalation
of spores. The usual incubation period is 40 to 50
days53 but may range from 21 to 106 days.52 Most
infections are asymptomatic but patients can present
with mild pneumonia; both conditions usually resolve. Inflammation may
accompany a syndrome of fever, chest pain, and
productive cough. Symptomatic conditions also
include a fulminant presentation and a chronic,
progressive, pulmonary disorder, with or without
dissemination.
Systemic Blastomycosis
When the fungus spreads from the lungs it produces systemic blastomycosis. The skin is the most commonly affected organ, involved in perhaps 50% of disseminated
cases. Bones, the genitourinary system (particularly
the prostate), and the central nervous system
also are involved frequently. In addition, there is
a less aggressive form of systemic blastomycosis in
which infection spreads exclusively to skin. About
40% of patients with disseminated blastomycosis
have inactive pulmonary disease. Skin lesions are usually few or solitary and are
located on exposed skin, often the face. They begin as inflammatory nodules that subsequently
break down to form expanding granulomatous
ulcers and plaques. Borders are raised and
have an annular, arcuate, or serpiginous pattern.
Lesions often expand asymmetrically with an exuberant,
verrucous, active edge. When the crusted
edges are removed, a granulomatous base studded
with minute pustules is revealed. Central healing
may leave a depigmented, atrophic scar. Oral and mucocutaneous ulcers also can occur. Bone infections sometimes produce fistulae extending to the
skin.
DIAGNOSIS
Direct examination of a smear of pus or sputum.
TREATMENT
Because most cases of acute pulmonary blastomycosis
probably resolve spontaneously, whether all persons should receive treatment remains unresolved. If untreated, pulmonary blastomycosis can reactivate years later. In general, patients with
active lung disease or with cutaneous involvement should receive therapy. An outpatient regimen of ketoconazole is generally effective. Because ketoconazole is distributed poorly in the central nervous system and is not excreted by the kidneys, it is not recommended for treating
meningeal or genitourinary blastomycosis. Intravenous amphotericin B is
recommended for immunocompromised patients or those with fulminant, refractory, or meningeal
disease. The triazole antifungal agent, itraconazole, has shown promise in preliminary investigations.