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Title: Bovine herpesvirus 1 infection in Norfolk : epidemiology and elimination
Author: Pritchard, Geoffrey Clive
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1993
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The epidemiology of bovine herpesvirus 1 (BHV1) infection in Norfolk was studied by scrutinizing records of submissions to Norwich Veterinary Investigation Centre and undertaking a cross-sectional analysis of serological findings from breeding herds in a disease monitoring scheme. Longitudinal studies examined the feasibility of eliminating BHV1 infection from individual herds by a test-and-cull programme and of maintaining seronegative status by employing security measures including serological screening of replacements. Alternative strategies were adopted in two heavily infected herds. A review of the appropriate literature and a description of the Norfolk cattle industry are also presented. Thirteen incidents of BHV1 fetopathy and 83 outbreaks of systemic infectious bovine rhinotracheitis (IBR), including 13 clinically mild low morbidity recrudescences in dairy herds, were confirmed between 1980 and 1989. These affected about 11 per cent of dairy herds and five per cent of suckler herds. Outbreaks occurred mainly during the winter months in rearing/fattening herds but throughout the year amongst adult breeding cattle. BHV1 antibodies were present in 510 (26.7 per cent) of 1908 sera and 122 (44.5 per cent) of 274 herds tested. There were no significant differences in antibody prevalence between herd types or between systemic illness and fetopathy submission categories but fewer sera from apparently healthy cattle were seropositive (Pc.001). Antibody prevalence increased significantly with age after three years. BHV1 antibodies were detected in the sera of 639 (15.1 per cent) cattle from 4219 aged at least two years in 56 scheme herds with no history of clinical IBR or IBR vaccination; almost 50 per cent of cattle aged 10 years or more were seropositive. Antibody prevalence amongst purchased cattle was much greater than in homebred cattle (Pc.001 in dairy herds, P < .05 in suckler herds). Reactors were present in 40 of the 56 herds: in seven herds more than 40 per cent of adult cattle were seropositive. In these high prevalence (HP) herds most cows seroconverted to BHV1 within two years of first calving whereas there was virtually no evidence of active infection in the 33 low prevalence (LP) herds. Maternally derived antibodies waned by about six months and young stock in infected herds subsequently remained seronegative provided they were kept apart from the cows and external sources of infection. BHV1 infection was readily eliminated from LP herds; serological freedom was retained during surveillance periods of up to four years by strict adherence to disease security rules. The repeated use of inactivated BHV1 vaccine to reduce virus shedding appeared to prevent further spread within an HP suckler herd; combined with partial segregation it was also used in the successful phased removal of reactors from an HP dairy herd within 30 months.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (D.V.M.S.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available