Bovine alphaherpesvirus-1 in bovine respiratory disease and semen samples

Background Bovine alphaherpesvirus 1 (BoAHV-1) remains one of the main primary pathogens involved in bovine respiratory disease in the United Kingdom (UK). It can also cause reproductive disorders and reduce semen quality. Therefore, it is vital to undertake testing to investigate the role of BoAHV-1 in respiratory disease outbreaks, where the disease is termed Infectious Bovine Rhinotracheitis (IBR), and for trade purposes to prevent virus spread through semen. In addition, IBR vaccines are widely used across the UK cattle industry to control IBR, making it important to monitor disease occurrence alongside vaccine use. Methods As part of cattle surveillance in England and Wales, a total of 1,040 clinical respiratory samples were tested by qPCR between November 2022 and March 2025, along with seven semen isolates from India. Results This testing undertaken enabled us to gain an insight into the BoAHV-1 role in the bovine respiratory disease complex (BRDC), its transmission dynamics, and its genetic variability. Fifty-two samples tested positive for BoAHV-1 DNA, representing an overall detection rate of 5%. The number of positive BoAHV-1 cases remained relatively stable over the study period with higher detection rates in late autumn and minimal cases in late summer and early autumn. BRSV, PIV3, and BCoV were also detected in co-infections with BoAHV-1. Furthermore, we compared phylogenetic trees generated using the genes recommended by the ICTV with those based on the UL44 gene, and its carboxy-terminal region to simplify and validate the UL44-based genotyping scheme. The phylogenetic analysis confirmed that UL44 genotyping produces phylogenies comparable to those obtained using the ICTV-recommended genes. Interestingly, all BoAHV-1 sequences obtained from clinical respiratory samples collected from UK herds grouped into both the 1.1 and 1.2 subtypes, with the majority belonging to subtype 1.1. The UK subtype 1.1 viruses were staggered along the phylogenetic branches. The seven Indian isolates analysed also grouped within the subtype 1.1 but formed distinct branches, indicating possible divergent evolution of the virus in Bos indicus or their crossbreeds. Conclusion This study has highlighted the shortfalls in our understanding of global diversity and epidemiology of BoAHV-1 and whether such diversities could impact the efficacy of currently available vaccines in Asian and African countries. Expansion of such collaborative studies to other countries especially those in Asia and Africa could broaden our understanding of the virus and would impact its global control and eradication through awareness of the virus economic impact and ease of control through co-ordinated vaccination.