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Title: Towards a greater understanding of contagious ovine digital dermatitis (CODD) : an epidemiological approach
Author: Angell, J. W.
ISNI:       0000 0004 6058 9523
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2016
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Contagious ovine digital dermatitis (CODD) is a cause of severe lameness in sheep in the UK. The aim of this study was to gain a greater understanding of this disease and provide practical information for application on farms. A cross-sectional postal survey of 511 farmers in Wales provided information on prevalence, geographical distribution and farmer reported risk factors. CODD was shown to be now endemic in the UK with 35% of farms affected, and an average on farm prevalence of 2.0% although some farms experienced a much greater prevalence. Larger farms were reportedly more at risk, as were those with bovine digital dermatitis (BDD) in their cattle. There has been a rapid increase in reports of CODD arriving on farms since 2000, and farmers considered concurrent footrot, buying in sheep, adult sheep, time of year and housing to be associated with CODD. A four-point ordinal locomotion scoring tool was developed enabling farmers and veterinarians to score the severity of a locomotion abnormality in sheep. This had high levels of intra-observer repeatability: weighted kappa (κW) 0.81 for veterinarians and 0.83 for farmers. A detailed clinical description and five-point lesion grading system were developed in order to aid diagnosis amongst veterinarians and farmers, and to aid communication. Radiographs also highlighted the extensive damage to soft tissues and bony structures that may occur in advanced clinical cases, and locomotion scoring demonstrated a variation in welfare impact by lesion grade. Histopathology provided detailed evidence of the pathological processes occurring in clinical lesions. Early lesions were characterised by a lymphoplasmacytic infiltrate of the distal digital skin, with suppurative coronitis and intracorneal pustules. In more advanced lesions there was complete separation of the dorsal hoof wall with a necrotizing and fibrinosuppurative exudate and dermatitis. Later lesions were mostly resolved, but with milder suppurative changes remaining within the cornified layer and periosteal reaction of the dorsal aspect of the distal phalanx. Immunohistochemistry revealed large numbers of treponemal-like organisms particularly within early lesion grades specifically associated with the histopathological changes. A longitudinal repeated cross-sectional field study of six farms with CODD over 16 months provided information on risk factors for CODD. Footrot was strongly associated with CODD at foot level OR: 7.7 (95%CI: 3.9-15.5), as were various pasture based factors. There was a temporal variation in the prevalence of CODD with increases observed in early Autumn and after housing. The minimum inhibitory/minimum bactericidal concentrations (MIC/MBC) of twenty CODD associated Treponema. spp isolates to ten antimicrobials were determined using a microdilution method, with penicillins and macrolides demonstrating the lowest MIC/MBC values. A cluster randomised controlled trial of 24 farms with CODD, using whole flock systemic metaphylactic tilmicosin, together with repeated treatment and isolation of clinical cases failed to eliminate CODD and footrot. The high failure rate (7/13 farms) was considered to be as a result of biosecurity breaches and one control farm managed to eliminate CODD without the whole flock approach.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available