No evidence of BoHV-1 exposure and low levels of pestivirus exposure in sera from 116 opportunistically sampled wild deer in Northern Ireland

Bovine Viral Diarrhoea Virus (BVDV), Border Disease Virus (BDV), and Bovine Herpesvirus-1 (BoHV-1, the cause of Infectious Bovine Rhinotracheitis, IBR), are economically important endemic viruses in ruminant livestock in the United Kingdom and Ireland. Deer could undermine control efforts in livestock by contributing to virus transmission and maintenance, but information on the presence of these viruses in the wild deer population is lacking. Blood samples from wild fallow and sika deer culled in Northern Ireland were collected opportunistically in the 2022-23 hunting season and tested using enzyme-linked immunosorbent assay (ELISA) for the presence of antibodies to these viruses (n = 116). No antibodies against BoHV-1 were detected. Antibodies against pestivirus were detected in three samples (2.6%), all from sika deer, and constitute the first report in this species in Europe. Virus strain differentiation by virus neutralization test (VNT) was inconclusive. Results therefore indicate no evidence of exposure to BoHV-1 and very low levels of pestivirus exposure in these deer populations. Based on these results there are currently no grounds to implicate deer as significant wildlife reservoirs of these viruses.