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Dermatophilosis

Martinez D.. 2012. In : Manual of diagnostic tests and vaccines for terrestrial animals : (mammals, birds and bees). Paris : OIE, p. 717-720.

Dermatophilosis (a/so known as streptothrichosis) is an exudative, pustular dermatitis that mainly affects cattle, sheep and horses. but also goats, dogs and cats, many wild mammals, reptiles and, occasionally, humans. The severe disease in ruminants is promoted by immunomodu/atory effects induced by infestation with the tick, Amblyomma variegatum. Laboratory diagnosis of dermatophilosis depends on the demonstration of the bacterium Dermatophilus congolensis in material from the skin or other organs. Sites other than the skin are rarely affected. Identification of the agent: Dermatophilus congolensis normally affects the epidermis, causing the formation of scabs. it may be demonstrated in smears made from scabs emulsified or softened in water or in impression smears from the base of freshly removed adherent scabs. The organism is Gram positive, but its morphology is more readily appreciated in smears stained with Giemsa. In stained smears, the organism is seen as branching filaments containing multiple rows of cocci. This characteristic appearance is diagnostic. In wet or secondarily infected scabs, only free cocci may be present, so that staining by immunofluorescence is necessary. Dermatophilus congolensis is demonstrated in histopathological sections by Giemsa staining or by immunofluorescence. Dermatophilus cheloniae may be found in crocodiles, chelonids and cobras. Isolation of D. congolensis from freshly removed scabs is straightforward, but the organism is readily overgrown by other bacteria. When cultured from contaminated sites, special techniques involving filtration, chemotaxis, or selective media are necessary. Demonstration and identification of D. congolensis by immunofluorescence is a reliable and very sensitive method of diagnosis, but requires that laboratories make their own diagnostic antisera as these are not available commercially. Although antigenic cross-reaction with Nocardia spp. has been reported, this is likely to give only weak fluorescence. Ideally, a monoclonal antibody specific to D. congolensis should be used. Polymerase chain reaction (PCR)-based characterisation has a/so been developed. Serological tests: A variety of serological tests has been used in studies of the epidemiology and pathogenesis of dermatophilosis. Antibody can be demonstrated in all but fetal blood in healthy ruminants, but the elevated levels associated with clinical infection can be used to identify animals that have been infected with the disease. Requirements for vaccines and diagnostic biologicals: Despite the identification of several

Mots-clés : immunologie; Épidémiologie; technique immunologique; identification; vaccin; test biologique; diagnostic; technique analytique; ruminant; maladie bactérienne; dermatophilus congolensis

Thématique : Maladies des animaux

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