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Doctoral thesis, 2013

Epidemiology and molecular tracing of bovine coronavirus and bovine respiratory syncytial virus infections in cattle herds

Bidokhti, Mehdi

Abstract

Bovine coronavirus (BCoV) and bovine respiratory syncytial virus (BRSV) are highly contagious pathogens that cause respiratory disease in cattle worldwide. BCoV is also associated with enteric disease in cattle of all ages. The aim of this thesis was to gain serological and molecular knowledge of BCoV and BRSV infections to help establish efficient future control in Sweden. In the first study, the prevalence of antibodies to BCoV and BRSV infections was studied in 20 conventional and 20 organic dairy herds in south-east Sweden. On two occasions, with a 1-year interval, 699 serum samples from 624 cows were tested by ELISA. The antibody prevalence to BCoV and BRSV was high (> 80%) at both sampling times. Conventional herds had a significantly higher seroprevalence than the organic herds (P < 0.01). There was a significant association (p < 0.001) of antibody prevalence and age of the cow, where titres were higher in older individuals. The findings in this study suggest that organic farm management routines may be effective in reducing the seroprevalence of these viruses. The second study was conducted on the molecular tracing of BCoV and BRSV throughout Sweden and also evolution of Betacoronavirus1. To investigate the molecular epidemiology of BCoV, the spike (S) gene of 27 PCR- positive samples from 2005 to 2009 were sequenced from 25 cattle herds. For BRSV, the glycoprotein (G) gene of PCR- positive samples during four years (2007 to 2011) were sequenced from 30 cattle herds. Sequence analysis revealed a high degree of identity among Swedish strains (> 97.7% for BCoV, > 94.5% for BRSV) regardless of clinical signs or animal age. Circulation of BCoV and BRSV between herds was found to occur throughout the year most often during the winter period. Identical sequences found in herds sampled within a few months' time suggested that these herds were part of a common transmission chain. Evolution analysis of the S gene of Betacoronavirus1 obtained since 1965 implies that BCoV strains are evolving genetically close to their human and canine counterparts. This study suggests that molecular analysis of strains can be a useful tool to support or rule out suspected transmission routes. Such knowledge is essential for the control of the spread of BCoV and BRSV between herds, regions and even countries.

Keywords

bovine coronavirus; spike gene; bovine respiratory syncytial virus; glycoprotein gene; epidemiology; organic; cattle herd; risk factors; molecular tracing; evolution

Published in

Acta Universitatis Agriculturae Sueciae
2013, number: 2013:34
ISBN: 978-91-576-7807-2
Publisher: Dept. of Clinical Sciences, Swedish University of Agricultural Sciences

Authors' information

Bidokhti, Mehdi
Swedish University of Agricultural Sciences, Department of Clinical Sciences

UKÄ Subject classification

Medical Bioscience

URI (permanent link to this page)

https://res.slu.se/id/publ/40691