APPROACHES TO PRIMING THE BOVINE NEONATE FOR THE PROTECTION AGAINST VIRAL RESPIRATORY DISEASES

Generation of immune responses to vaccination is challenging in the young bovine because of high concentrations of circulating maternally acquired antibody in young calves. Poor humoral responses to vaccination at a young age combined with waning of maternal antibody concentrations overtime result in overall low circulating antibody at the high disease risk peri-weaning period. While, humoral immunity is not induced by systemic vaccination in the face of maternal antibodies (IFOMA). Protective short duration IgA responses can be induced through intranasal (IN) administration of vaccine IFOMA, but typically this protection does not last to the peri-weaning period. Mucosal immune responses have been shown to provide some systemic priming which might respond to boosting vaccination later in life. The main objective of these studies was to determine if mucosal priming and systemic boosting could effectively generate immune responses and cause clinical protection from disease caused by viral pathogens associated with bovine respiratory disease in the peri-weaning period.\n Initially a comparison of clinical protection and immune responses to viral challenge was made between calves either neonatally IN primed and boosted with a subcutaneous (SC) vaccine or primed with a SC vaccine at the same time the IN primed calves were boosted. The calves were challenged with bovine parainfluenza virus type 3 (BPIV3) and bovine respiratory syncytial virus (BRSV) at weaning. The study found that the IN primed calves had no fever, less indication of lung lesions and shed less virus post-challenge.\n Bovine coronavirus (BCoV) is important to the BRD complex, but little work has been done to investigate BCoV vaccination for control of BRD. As a first step an immune response study was conducted comparing virus neutralizing (VN) antibody responses among neonatal calves that were differentially vaccinated against BCoV. When neonatal calves were IN prime and boosted with an intramuscular (IM) [IN-IM] and compared to unvaccinated control [CON], IN primed [IN-BO] and IM primed and boosted calves [IM-IM], it was found that only the IN-IM calves had the highest VN concentrations and was the only group to have an anamnestic BCoV VN response. The effect of differentially boosting with either a modified live virus (MLV) or inactivated virus (KV) vaccine was also investigate. The study found no differences in BCoV specific or VN antibody concentrations between boost types. Overall, these studies showed anamnesis at weaning to IN prime-systemic boost vaccination at a young age.\n Next, virus co-infection compared calves IN primed as neonates that were differentially boosted with either MLV or KV vaccine. At weaning calves were infected with BCoV, BPIV3 and BRSV. Overall there were mild clinical signs observed for both groups. BCoV VN anamnestic responses were found for both groups, but only the IN-KV group showed anamnesis for BPIV3 and BRSV. Post infection shed of virus showed IN-MLV shed less BCoV, but more BPIV3 and BRSV than IN-KV. Effect of differential boost with KV or MLV depends on the specific virus being studied.\n Next, a study looking at natural exposure to BCoV in the peri-weaning time period found that commercial vaccines were effective in reducing BRD treatment rates for at least one commercial vaccine (V1) compared to the non-BCoV vaccinated control calves (CTL). It is important to note that the treatment rates for the other vaccine (V2) group’s treatment rates were neither different from V1 nor CTL. The results might indicate that the V2 was either not effective or not as effective as the V1. The V2 vaccine might not induce protection against contemporary BCoV strains or herd immunity might have protected CTL.\n The final study looked at differential boost with KV (IN-KV) or MLV (IN-MLV) of IN primed neonates that were then challenged with BVDV type 2 at weaning. Key findings included less clinical disease, shorter duration of fever, and higher white blood cell counts among MLV boosted calves. Both groups showed anamnesis, IN-MLV had higher VN antibody concentrations and shed less virus.\n Altogether, these studies found clinical protection and robust immune responses among IN primed-systemic boosted calves. Differential boosting IN primed calves indicated some response differences among viruses that should be further investigated. These data show that veterinarians should consider IN prime and systemic boost programs for control of BRD associated viruses.

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