Blastomycosis

by Jamye Coffey

Blastomycosis is also known as the Chicago Disease, Gilchrist's Disease, and North American Blastomycosis. In 1894, Gilchrist discovered the first case of Blastomycosis in America (10). It is most common in Southeastern United States, the Mississippi River valley, Southern Canada, and Central America.

The disease is caused by the dimorphic fungus, Blastomyces dermatitides (3). Living conditions for this fungus are quite strict. They only flourish in an environment with a moist substrate, no direct sunlight, available organic debris, and a pH less than 6 (1). Due to the infrequent isolation in nature of the organism the etiological niche and virulence factors are uncertain (5) (8).

The fungus Blastomyces dermatitides once inhaled will attach to the lungs causing pulmonary lesions. These lesions induce an inflammatory response due to the presence of macrophages, neutrophils and granulomata (4). The fungus is thermally dimorphic, and morphology can be made at 24 and 37 degrees. At 24 degrees a mould is present and grow anywhere from slow to moderately quick. Colony is .5 to 3 cm in diameter, globular in shape and requires 7 days of incubation on potato glucose agar. Unicellular hyphae and unbranched conidiophores can be seen. At 37 degrees a yeast is present and grows anywhere from slow to moderately quick. Colony is .5 to 3 cm in diameter, thick cell wall that is globular in shape and requires 7 days of incubation on enriched medium. Fungus appears as budding yeast, with 2-5 nuclei per cell, and a broad base attaching the bud to parent cell (1).

Chest x-rays and blood tests are the first step in diagnosis blastomycosis. Once in the lab the samples of sputum and skin or tissue biopsy are put through many more tests. Some of the best tests are direct cultures onto Sabouraud glucose agar, brain heart infusion agar, yeast-extract-phosphate agar, and medium with cycloheximide (2). Other important tests include KOH preparation, special stains, and measurement of complement fixing antibodies to various antigens (4). Some developed DNA probes and exoantigen technology has been used to test for blastomycosis (6).

The fungus is transmitted through inhalation or contact with spores in the soil through cuts and scrapes (9). It is a rare disease that affects humans and dogs. Those most likely to be exposed are campers, farmers, hunters, and forest workers. The largest percentages of patients that test positively to blastomycosis are middle-aged males and those who are immunosuppressed. Since it is a rare disease it is not uncommon for cases to be misdiagnosed for weeks if not months.

Those affected with Blastomyces dermatitides have varied symptoms and signs of the disease. It can take anywhere from weeks to months to show the first signs. Many develop a fever and dry cough and progress to weight loss, chest pain, and a cough with thick sputum (6). Other symptoms include pulmonary infiltrates, bone lesions, skin lesions, and a rash (ulcerative) (8). Clinical manifestations of blastomycosis include acute pulmonary disease, subacute and chronic pulmonary disease, disseminated extrapulmonary disease involving the bone, the genitourinary tract, and central nervous system (7). It varies among patients how the disease will affect the body. Some patients will spontaneously get better, while some will die from the disease.

Patients are typically treated with itraconazole (Sporanox), ketoconazole (Nizoral) and amphotericin B (Fungizone) (9). Amphotericin B is given intravenously for 4 to 10 days followed by itraconazole treatment for 2 to 6 months. The only way to prevent obtaining the disease is to avoid areas in which the fungus lives.

References

(1)Blastomyces sp. Updated 2/6/2002. http://www.doctorfungus.org/thefungi/blastomyces.htm 4/25/2002.

(2)Blastomycosis. Updated 2/6/2002 http://www.doctorfungus.org/mycoses/human/blasto/blastomycosis.htm 4/25/2002.

(3)Blastomycosis. Written 12/2002. http://www.cdc.gov/ncidod/dbmd/diseaseinfo/blastomycosis_t.htm 4/23/2002.

(4)Infectious Disease: Blastomycosis. Updated 6/16/1998. http://www.mc.vanderbilt.edu/peds/pidl/infect/blastomy.htm 4/23/2002.

(5)Volk, Tom. Tom Volk's Fungus of the Month for January 2001. Updated 1/2001. http://botit.botany.wisc.edu/toms_fungi/jan2001.html 5/2/2002.

(6)Disease Fact Sheet Series: Blastomycosis. Updated 7/2/2001. http://www.dhfs.state.wi.us/healthtips/BCD/Blastomycosis.htm 5/6/2002.

(7)Blastomycosis -- Wisconsin, 1986-1995. Updated 7/10/1996. http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/00043101.htm 5/6/2002.

(8)Blastomyces dermatitides. Updated 4/13/1999. http://www.medinfo.ufl.edu/year2/mmid/bms5300/bugs/blastder.html 4/25/2002.

(9)Davidson, Tish. Blastomycosis. Written 1999. http://www.findarticles.com/cf_dls/g2601/0002/2601000206/p1/article.jhtml 5/6/2002.

(10)Excerpt from Blastomycosis. http://www.emedicine.com/med/byname/blastomycosis.htm 5/6/2002.