Characterization of a Highly Virulent Noncytopathic Bovine Viral Diarrhea Virus 2b Isolate Detected in Cattle in Inner Mongolia, China.

Bovine viral diarrhea virus (BVDV) infection causes subclinical to severe acute disease in cattle all over the world. Two genotypes of BVDV are recognized, BVDV1 and BVDV2. Currently, the subtypes of BVDV1b and BVDV2a are mainly circulating in China. Here, a newly noncytopathic (ncp) BVDV strain named BVDVNM21 was isolated and identified from cattle. We determined the complete genome sequence of BVDVNM21, phylogenetic analysis of 5' untranslated region (5'UTR), N, and E2 gene, and complete genome showed the virus belongs to BVDV2b subtype and formed an independent clade within BVDV2b. Genome-wide sequence analysis showed that BVDVNM21 had high homology with SD1301 (98.10%) isolated from China. In the experimental infection study of guinea pigs and calves, they all developed similar clinical signs, including a pronounced and prolonged febrile response lasting more than 3 days and pronounced reduction in white blood cells (WBC) and platelets of more than 40%. Moreover, guinea pigs showed more acute infection characteristics after infection, and WBC decreased by more than 50% at 1 day postinfection (dpi), and they recovered in less than 3 days. The results indicated that the BVDVNM21 strain showed high virulence in calves. It was the first confirmed isolation of a highly pathogenic ncpBVDV2b in cattle, as well as the establishment of the BVDV-guinea pig model. This study may provide a basis for further research and control of the prevalence of BVDV2b in China.