Abstract: The study focused on analysis of the molecular characteristics and genetic evolution of the antigen gene E^rns of different subgenotypes of bovine viral diarrhea virus (BVDV) in northwest China from 2013 to 2019. Total RNA was extracted from 150 EDTA-anticoagulated blood samples sent for BVDV detection, which were collected from cattle suspected of BVDV infection on large-scale farms in Gansu, Qinghai provinces and Ningxia Hui Autonomous Region. The RNA samples were submitted for RT-PCR with primers targeting at the E^rns-E1 region of the viral genome, followed by cloning, sequencing, and genetic evolution analysis by constructing phylogenetic trees. The virus of individual BVDV subgenotype identified in the samples was isolated with Madin-Darby bovine kidney (MDBK) cells, followed by biotype determination. Results were as follows: The overall BVDV positive rate was 37.33% by RT-PCR, with positive rate of 37.68%, 35.71% and 40.00% in Gansu Province, Qinghai Province and Ningxia Hui Autonomous Region respectively. E^rns-E1 DNA was obtained by RT-PCR from 56 blood samples and 33 different E^rns coding sequences with 681 bp in length were harvested by cloning and sequencing. Sequence analysis showed that the epidemic strains belonged to 10 BVDV genotypes: two within BVDV-1a, five within BVDV-1b, one within BVDV-1c, three within BVDV-1d, 11 within BVDV-1m, one within BVDV-1o, four within BVDV-1p, four within BVDV-1q, one within BVDV-1v, and one within BVDV-2a. One non-cytopathogenic BVDV isolate of individual subgenotype of BVDV-1a, BVDV-1b, BVDV-1v, BVDV-2a and two isolates of BVDV-1d susgenotype were obtained. Higher nucleotide similarity of E^rns gene among different strains within individual subgenotype was observed in the classical subgenotype BVDV-1a to 1d (79.8%-85.9%) or in BVDV-1m to 1q and the novel subgenotype 1v (81.0%-87.3%), with the highest nucleotide similarity shared by strains within BVDV-1m and BVDV-1p (87.3%). The RNase active sites and the dsRNA-interacting motif (₁₃₉KKGK₁₄₂) were conserved among strains within individual subgenotype while the N-glycosylation site at position N26 (26 NRSL) was translocated (24 NVSR) in strains within the 1m to 1q and 1v subgenotype. For the first time, a phylogenetic tree based on the nucleotide sequences of E^rns gene was constructed, illustrating the close genetic relatedness in the evolution among strains within subgenotypes 1m to 1q and 1v. For the first time, the E^rns gene was selected as a target for homology and phylogenetic analysis of BVDV of bovine origin from Gansu, Qinghai provinces and Ningxia Hui Autonomous Region in northwest China. Epidemic strains within 10 subgenotypes were detected, with the BVDV-1m subgenotype being the most prevalent and close genetic relationship shared by BVDV strains within BVDV-1m to 1q and 1v subgenotypes.

Key words: bovine viral diarrhea virus, E^rns gene, genetic evolution