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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Cryptococcus, Histoplasma, Coccidioides, and Other Systemic Fungal Pathogens

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Blastomycosis : Clinical Aspects

Because mild cases are difficult to diagnose, most infections are recognized at advanced or disseminated stages of the disease.

BLASTOMYCOSIS : CLINICAL  ASPECTS

MANIFESTATIONS

Because mild cases are difficult to diagnose, most infections are recognized at advanced or disseminated stages of the disease. This problem was also posed by the other systemic mycoses before the development of sensitive and specific diagnostic procedures. Pul-monary infection is evidenced by cough, sputum production, chest pain, and fever. Hilar lymphadenopathy may be present, as may nodular pulmonary infiltrates with alveolar consolidation. The total picture may mimic a pulmonary tumor, tuberculosis, or some other mycosis. Skin lesions are common and were once considered a primary form of the disease. In contrast to histoplasmosis, lesions develop on exposed skin; mucous mem-brane infection is uncommon. Extensive necrosis and fibrosis may produce considerable disfigurement. Bone infection has features similar to those of other causes of chronic os-teomyelitis. The urinary and genital tracts are the most commonly affected visceral sites; the prostate is especially prone to infection.

DIAGNOSIS

Direct demonstration of typical large yeasts with broad-based buds (blastoconidia) in KOH preparations is the most rapid means of diagnosis. Biopsy specimens also have a high yield, and the organisms are visible with either H&E or special fungal stains. B. der-matitidis grows on routine mycologic media, but culture may take as long as 4 weeks.Conidia are not particularly distinctive, and demonstration of dimorphism and typical yeast morphology is essential to avoid confusion with other fungi. The immunodiffusion test is particularly useful in differentiating cultures from Histoplasma. Serologic tests are available but may be negative in up to 50% of cases. Skin tests are no longer available.

TREATMENT

Although amphotericin B is the preferred therapy, it is used only for progressive or disseminated disease. As with other systemic mycoses, response to treatment is slow, and relapse is common. Itraconazole, ketoconazole, and fluconazole have been effective in nonmeningeal cases and for suppression in AIDS. These azoles are considered alternatives to amphotericin in immunocompetent patients if the disease is not severe.

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