Sporotrichosis, Biology


Sporotrichosis is subacute or chronic infectious disease caused by a dimorphic fungus, Sporothrix schenkii which occurs commonly in soil, wood and vegetation. The disease is characterized by nodular lesions and ulcers in the lymphnodes, skin and subcutaneous tissues. Very rarely dissemination is through bone, lung, liver, spleen and other internal organs. Infection is established through the traumatic implantation of fungus into the subcutaneous tissue by the contaminated splinter or thorn. As a result, chronic pyogenic granulomatous infection develops. Cases have been reported in man, horse, donkey, mule, cattle, camel, dog, cat, chimpanzee and rat.

In horse, mule and donkey, small, multiple cutaneous nodules develop on the lower part of the limb. These nodules are painless which later ulcerate and discharge small amount of pus. The infection spreads through lymphatic vessels which become thickened and corded. Sometimes, a non-ulcerating and disseminated form of disease without the involvement of lymphatics has been observed in horse. The disease in dog is usually more fatal as infection spreads to the visceral organ including bone. In man, localized lesions are found on hand, arm and leg. The disease is more frequent in persons engaged in agriculture and forest work. Its outbreak has been recorded in gold miners in South Africa as the fungus occurs on timber in humid mines.
Diagnosis: Diagnosis is confirmed by the isolation of causative fungus on Sabouraud‘s medium or BHI agar. The culture on cysteine glucose blood agar medium yields soft, greenish-yellow bacterial type colonies at 37°C. Smear from pus and other infected material may be examined microscopically for Cigar-shaped bodies after staining with Giemsa or silver methanamine method. Pathogenicity test may be conducted in white mice or rat which shows granulomas in the mesentery besides peritonitis. Male mouse, if inoculated with the positive clinical specimen intra- testicularly, develops severe type of orchitis, and the exudate from testis will reveal Cigar-shaped-bodies in the direct microscopy. Serological tests particularly tube and latex agglutination may also help in diagnosis. Clinically, the disease may be mistaken for epizootic lymphangitis or ulcerative lymphangitis. Microscopical examination of pus smear will differentiate all these disease.

Treatment and prevention:
Animal sporotrichosis is best treated with potassium iodide orally or sodium iodide intravenously. Tincture of iodine may be applied daily externally on the ulcers. The sick animal may be isolated; proper disinfection of harness, gear, bedding and other equipment will prevent the spread of infection. Amphotericin B is being used in human infection. The persons employed in horticulture or forest work may use gum-boots to avoid the traumatic injury to the leg.

Posted Date: 9/17/2012 8:41:44 AM | Location : United States

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