Genomic evolutionary features and pathogenicity of bovine herpesvirus type 1.2b circulating in China

Bovine herpesvirus type 1 (BoHV-1) is a major pathogen causing the bovine respiratory disease complex (BRDC), yet the molecular features of circulating subtypes in China remain insufficiently defined. In this study, two BoHV-1 strains were isolated from cattle with respiratory disease on the same farm, and one strain, designated SZ202201, was selected for whole-genome sequencing. Similarity analysis identified the Chinese BHV SHJS strain as its closest relative. Phylogenetic reconstruction placed SZ202201 within the BoHV-1.2b lineage, which has become the predominant and most genetically diverse genotype circulating in China since 2019. Phylogenetic analyses of gB, gC, and gD revealed substantial genetic divergence between the field BoHV-1.2b strains and the currently used BoHV-1.1 MLV vaccine. Neutralization assays indicated that the BoHV-1.1 MLV vaccine can still elicit measurable antibody responses against BoHV-1.2 strains. Most major functional proteins of SZ202201 were conserved, whereas gB and gD contained distinct mutations within their immunoreactive regions. Strong positive selection was detected on gB, gC, gD, gE, and gG, indicating that some strains, including this isolate, are undergoing adaptive evolution related to immune escape. Recombination analysis of 55 complete genomes identified 29 events, occurring predominantly among BoHV-1.2b strains, and SZ202201 harbored one cross-regional recombination event. SNP profiling effectively distinguished vaccine-related strains from field isolates and further defined genotype-specific markers. In guinea pigs, SZ202201 induced the most severe clinical disease compared with two other BoHV-1.2b isolates. These findings provide an important basis for developing precise and effective control strategies for BoHV-1 in China.