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Title: A study of the epidemiology and controls of Corynebacterium pseudotuberculosis infection in sheep in the United Kingdom
Author: Baird, Graham J.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2011
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This thesis is a distillation of work carried out by the author and others between 1999 and 2010. The overarching objective was to achieve a better understanding of the epidemiology and prevalence of ovine caseous lymphadenitis within the UK sheep industry. Using that knowledge, means by which the disease could be controlled were then evaluated. Throughout this process the existing knowledge of Corynebacterium pseudotuberculosis and the diseases that it causes, provided a foundation on which these further developments were built. Although C. pseudotuberculosis infection has been recognised in the UK for a comparatively short period, it has been a cause of significant disease in various animal species around the globe for many decades. A comprehensive review of C. pseudotuberculosis disease and related research was therefore an essential starting point for consideration of the infection in this country. The use of phospholipase D ELISA tests has been an established tool of CLA research in other countries. Using a recently developed ELISA assay and blood samples collected from around GB for the Sheep Health Scheme, the prevalence of CLA within the terminal sire sector of the British sheep industry was assessed. Seropositive animals were detected in 18% of the 745 flocks tested, with the Charollais breed showing the highest apparent prevalence. In response to concerns within the dairy goat sector regarding milk hygiene in CLA affected herds, the ability of normal commercial pasteurisation techniques to kill C. pseudotuberculosis organisms in milk was established. The potential of using CLA ELISA and Western blot assays to control and eradicate the disease was studied: first in a number of lowground terminal sire flocks and then in a large upland commercial flock. In both situations a policy of test and cull was shown to be effective in substantially reducing clinical manifestations of disease. Complete eradication was found to be achievable under certain circumstances. In a lowground flock where initial seroprevalence was greater than 60%, a complete absence of clinical disease and a seronegative status was achieved. In a large upland flock, seroprevalence was reduced from 10% to 0.4%. More significantly, the incidence of clinical CLA in this flock, which in 2007 was approximately 5% amongst the adult animals, was reduced to zero for a period of two years from June 2008. Vaccination, which forms the mainstay of CLA control efforts in many parts of the world, was assessed for its potential for disease control in the UK. The market-leading proprietary vaccine was compared with three experimental vaccines in its ability to confer protection against bacterial challenge. A recombinant PLD and bacterin combined vaccine was shown to confer the most effective protection.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.V.M.S) Qualification Level: Doctoral
EThOS ID:  DOI: Not available