Prevalence and risk factors for Bovine Herpesvirus Type 1 (BoHV-1) infection in Irish beef herds: results from the National Beef Welfare Scheme 2023

Infectious bovine rhinotracheitis (IBR), caused by bovine herpesvirus-1 (BoHV-1), is a highly contagious disease with significant economic impacts on the cattle industry. It can also lead to respiratory distress, reproductive losses and compromised animal welfare, and thus represents a key target for control. This study aimed to assess the prevalence and identify risk factors associated with BoHV-1 infection in Irish beef herds. Conducted under the National Beef Welfare Scheme (NBWS), the study involved testing 10,659 beef breeding herds, representing approximately 20% of the national beef herd population. A total of 189,404 animals were tested. Using a 'snapshot' testing strategy herd-level BoHV-1 status was determined based on the presence of antibodies to the gE glycoprotein in up to 20 randomly selected animals, preferably over 9 months of age to exclude maternally derived antibodies. Vaccination histories were not available for participating herds. Results indicated an animal-level apparent prevalence of 11.4% and a herd-level apparent prevalence based on positive snapshots of 48.8% (defined as herds with ≥ 1 positive animal). Larger herds and high rates of animal in-moves per capita (here, > 17% of herd replaced by purchases in the past year) were identified as significant risk factors for recent (within the last three years) BoHV-1 circulation. Previous studies had indicated a herd-level prevalence in Ireland of up to 80%. The lower prevalence estimates identified in this study may reflect improved biosecurity and vaccination uptake in recent years. The findings from this survey, although showing that BoHV-1 is still endemic in Irish beef herds, provide updated prevalence figures which are considerably lower, indicating that a higher number of farms would be in a position to achieve freedom from BoHV-1 in a relatively short period. These results offer essential epidemiological insights to inform the design and implementation of a national BoHV-1 control programme in Ireland.