Evaluation of passive immunity and different vaccination protocols on the induction of local and systemic antibody responses and clinical protection of beef calves against experimental infection with bovine respiratory syncytial virus (BRSV)
Type of DegreePhD Dissertation
General Veterinary Medicine
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Bovine respiratory syncytial virus (BRSV) is one of the most prevalent viruses associated with the bovine respiratory disease complex (BRDC). The persistency over time and role of local and systemic antibodies against BRSV transferred from maternal colostrum is not completely understood. Additionally, the efficacy of vaccination of calves on providing clinical protection against experimental infection with BRSV or natural occurrence of BRDC is inconsistent in the literature. The objective of this research was to review the literature on the effect of BRSV vaccination, evaluate the effect of local and systemic BRSV antibodies derived from colostrum, and evaluate the effect of different vaccination protocols with MLV BRSV vaccines on the induction of local and systemic antibody responses and clinical protection of beef calves against experimental viral infection. Results from the meta-analysis indicated that commercially available MLV BRSV vaccines reduced the risk of calf mortality after experimental infection with BRSV. Modified- live virus vaccines reduced the risk of morbidity following experimental infection in calves with absence of serum BRSV antibodies at initial vaccination, but failed to demonstrate significant morbidity reduction when calves were vaccinated in the face of maternal antibodies (IFOMA). The results from these studies suggest that the presence of colostrum-derived SN antibody titers and BRSV IgG1 transferred to the upper respiratory tract of newborn calves likely plays a role in clinical protection against clinical disease (morbidity) early in life; however, the presence of systemic and local colostrum-derived antibodies interfere with the induction of adequate/complete immune responses to IN MLV vaccination during the first month of life. 2 Modified-live virus IN vaccination of neonatal calves during the first hours of life and before complete transfer of specific BRSV antibodies from colostrum did not result in priming of nasal BRSV IgA responses following vaccination. Additionally, IN MLV vaccination of neonatal calves did not result in significantly different upper respiratory tract BRSV IgA titers following exposure to BRSV later in life when compared with control calves. A combination SC-IN MLV vaccination protocol at branding and at weaning, respectively, or IN MLV vaccination at weaning alone did not provide clinical advantages nor resulted in SN antibody response differences compared with no vaccination following challenge of calves shortly after IN vaccination. The upper respiratory tract BRDC-associated bacteria were altered by either IN MLV BRSV and BHV-1 MLV, simultaneous experimental challenge with BRSV and BHV-1 or both in weaning age beef steers.