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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Dermatophytes, Sporothrix, and Other Superficial and Subcutaneous Fungi

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Sporotrichosis

S. schenckii is a ubiquitous saprophyte particularly found in hay, moss, soil, and decayingvegetation, and on the surfaces of various plants.

SPOROTRICHOSIS

 

EPIDEMIOLOGY

S. schenckii is a ubiquitous saprophyte particularly found in hay, moss, soil, and decayingvegetation, and on the surfaces of various plants. Infection is acquired by traumatic inocula-tion through the skin of material containing the organism. Exposure is largely occupational or related to hobbies. The skin of gardeners, farmers, and rural laborers is frequently trau-matized by thorns or other material that may be contaminated with conidia of S. schenckii. An unusual outbreak of sporotrichosis involving nearly 3000 miners was traced to S. schenckii in the timbers used to support mine shafts. A 1988 outbreak covered 15 statesand was traced to sphagnum moss. Infection is occasionally acquired by direct contact with infected pus or through the respiratory tract; these modes of infection, however, are much less common than the cutaneous route.

PATHOGENESIS

Both the conidia and yeast cells of S. schenckii are able to bind to extracellular matrix proteins like fibronectin, laminin, and collagen. This may aid their survival in the early stages of infection. Local multiplication of the organism stimulates both acute pyogenic and granulomatous inflammatory reactions. Melanin production may provide resistance to oxidative killing. Proteinases similar to those seen in other fungal pathogens are present but no connection to virulence has been established. The infection spreads along lymphatic drainage routes and reproduces the original inflammatory lesions at intervals. The organisms are scanty in human lesions.

IMMUNITY

The cellular response to S. schenckii is mixed. The increased frequency and greater sever- ity of disseminated disease in patients with T-cell defects points to CMI as the primary immune mechanism. Antibody plays no known role in immunity.

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