Blastomycosis pathophysiology On the Web
American Roentgen Ray Society Images of Blastomycosis pathophysiology
Blastomycosis is caused by a dimorphic fungi called Blastomyces dermatitidis. It has an average incubation period of 3 weeks to 3 months after exposure. The initial neutrophilic response and the subsequent cell-mediated immune response are manifested as a suppurative tissue destruction seen in lungs, skin, and other organs. The histopathological hallmark findings on sputum microscopy is the multinucleated yeast form (budding).
- Inhalation of the conidia from its natural soil habitat is considered the most significant route of transmission.
- Other less common route of transmission is by cutaneous inoculation through direct skin injury.
- The incubation period varies from 3 weeks to 3 months after exposure.
- Once inhaled in the lungs, the conidia are mostly destroyed due to their susceptibility to neutrophils, leukocytes and macrophages. 
- However, a few conidia escape this protective mechanism and evolve into yeast form, which being double walled structures are more resistant to destruction.
- This conversion releases a glycoprotien BAD-1, which induces cell mediated immunity. 
- This results in a pyogranulomatous response at the primary site of infection (lungs).
- Which eventually leads to the formation of a non-caseating granulomas.
- The fungi can disseminate through the blood and lymphatics to other organs, such as skin, bone, genitourinary tract and brain.
- Cyotoxic T cells are mainly responsible for persistence of infection and tissue damage.
- Ineffective type 4 delayed hypersensitivity reaction containing macrophages and sensitized T cells are mainly responsible for the cutaneous manifestations. 
There is no known genetic association for blastomycosis.
Classic appearance on modified Wright's stain 
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