Isolation and identification of a potential new bovine viral diarrhea virus genotype associated with severe outbreaks in yaks (Bos grunniens) in China.

Bovine viral diarrhea virus (BVDV) is a globally significant pestivirus currently classified into three species: BVDV-1 (Pestivirus A), BVDV-2 (Pestivirus B), and BVDV-3 (HoBi-like, Pestivirus H). Here, we report the isolation and identification of a potential new BVDV genotype associated with severe outbreaks in yaks in China. Since 2024, an epidemic characterized by respiratory and gastrointestinal symptoms has been spreading across Sichuan and Qinghai Provinces. From January 2024 to October 2025, we collected 260 samples from 167 affected yaks from 14 farms. Among these, 55.69% of the yaks and all sampled farms tested positive for BVDV. Sequencing of the 5' untranslated region (5' UTR) and Npro fragments from clinical samples revealed that the dominant epidemic strains may represent a novel BVDV lineage. We isolated four cytopathic strains and successfully sequenced two genomes of strains SC-H03 and QH-B04, which share less than 77.8% nucleotide identity across the complete coding sequence (CDS) with well-defined BVDV-1/2/3 strains. Phylogenetic analyses of the complete CDS and individual genes placed SC-H03 and QH-B04 in a distinct monophyletic clade with strong bootstrap support. Pairwise genetic distances confirmed substantial divergence, and cross-neutralization assays revealed significant antigenic differences from BVDV-1 and BVDV-2 reference strains. In accordance with ICTV Pestivirus classification standards, these strains satisfy the criteria for a new Pestivirus species, which we propose to name BVDV-4 (Pestivirus T). Given its wide prevalence in yaks and association with high morbidity and mortality, our findings underscore the urgent need for targeted prevention and control measures.