Epsilon Open Archive

Abstract

This thesis deals with the dynamics of bovine respiratory syncytial virus (BRSV), bovine parainfluenza virus 3 (PIV-3) and bovine coronavirus (BCoV) infections in Swedish cattle herds. It also describes the development of a fluorogenic reverse transcription (fRT)-PCR for BRSV diagnosis. Furthermore, BRSV immunostimulating complexes (ISCOMs) and a commercial inactivated BRSV vaccine were evaluated in vivo in calves. By serology, high incidences of PIV-3 and BCoV, and a lower incidence of BRSV, were demonstrated in 118 herds in one area of Sweden and at a Swedish bull testing station for beef breeds. In the dairy herds, absence of these infections and bovine viral diarrhea virus (BVDV) was correlated to absence of respiratory disease, confirming the clinical importance of the viruses. There appeared to be a geographical clustering of BRSV and BCoV infected herds and infections were as common in herds that did or did not introduce new animals, indicating indirect transmission between herds. At the bull testing station, an effective spread of virus within the herd was demonstrated. BRSV was involved in a disease outbreak, emphasizing the need for effective means to prevent this infection. By testing animals prior to admission, the bull testing station was kept free from BVDV during a six-year study period. A single tube BRSV fRT-PCR was shown to be a sensitive, specific and rapid tool to detect BRSV in both naturally and experimentally infected animals. The assay required less laboratory time, had a lower risk of contamination and allowed higher sample throughput than a nested PCR with a comparable sensitivity. Accordingly, the fRT-PCR is suitable for BRSV research as well as for routine diagnostic purposes and was used in the vaccine evaluation. The immunogenicity and protection induced by BRSV-ISCOMs were evaluated and compared to those induced by a commercial vaccine (CV) in calves. An experimental BRSV challenge was used for this purpose. The ISCOMs induced rapid humoral immune responses and strong clinical and virological protection despite maternal antibodies in calves at vaccination. In contrast, calves vaccinated with the CV and control calves all shed virus and developed moderate to severe respiratory disease after challenge. Thus, BRSV-ISCOMs are promising candidates for future industrial production after further evaluation and may also be used to investigate protective immunological parameters against BRSV. The CV needs to be further evaluated in controlled field trials.