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Studies on the diagnosis, epidemiology and immunity of Corynebacterium pseudotuberculosis infection in sheep

Robertson, Judith Patricia (1980) Studies on the diagnosis, epidemiology and immunity of Corynebacterium pseudotuberculosis infection in sheep. Masters by Research thesis, Murdoch University.

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Abstract

The gel diffusion test for detecting antibodies to Corynebacterium pseudotuberculosis exotoxin was developed for the diagnosis of caseous lymphadenitis (CLA). Although it was not a definitive test for CLA it detected 78 per cent of sheep with CLA lesions, being more sensitive than the anti-haemolysin-inhibition test which detected C. pseudotuberculosis antitoxin in 62 per cent of sheep with CLA. Antibodies to the toxin were also commonly detected in sheep in which CLA lesions were not found but were considered to result from prior exposure to C. pseudotuberculosis with internal lesions either failing to develop or regressing. The serum agglutination and gel precipitation tests for the detection of antibodies to C. pseudotuberculosis bacterial cell were found not to be sufficiently sensitive for the diagnosis of CLA.

Enrichment and selective media incorporating potassium tellurite. polysorbate 80 and/or nitrofurazone, in conjunction with anaerobic incubation, were developed for the cultural isolation of C. pseudotuberculosis from the sheep and its environment. Using these media C. pseudotuberculosis was isolated from infected shear cuts, the respiratory tracts (including buccal cavities) of sheep with lung lesions and used dipwashes. Isolation of the organism in low numbers from sheep faeces was not successful. Corynebacterium pseudotuberculosis was found to survive up to 17 weeks in cool sheltered sites in the shearing shed environment but no longer than two weeks when exposed to sunlight.

Epidemiological studies, using serological monitoring to determine the incidence of CLA, indicated that activities associated with shearing and dipping appeared to be the main cause of spread of CLA, with dipping being the means of a mechanical transfer of the causative organism. Delaying the time of dipping to several weeks post shearing and separating non-infected sheep from infected sheep and probable C. pseudotuberculosis contaminated environments during and for six weeks after shearing and dipping helped to reduce the prevalence of CLA, however, none of these practices appeared to be sufficiently effective for long term control of CLA.

A stable, pathogenic streptomycin-resistant strain of C. pseudotuberculosis was produced for use in immunological studies. Resistance to reinfection by C. pseudotuberculosis appeared to be high in CLA infected sheep. Vaccination with a toxoid formed from the crude C. pseudotuberculosis toxin was effective for the protection of sheep against C. pseudotuberculosis when experimentally challenged.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation: School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: repository@murdoch.edu.au. Thank you.
Supervisor(s): Nairn, Malcolm
URI: http://researchrepository.murdoch.edu.au/id/eprint/53472
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