Bovine viral diarrhea virus (BVDV) is a great economically pathogen in cattle and other ruminants in the world [1–10]. The virus is associated with several clinical symptoms, including diarrhea, respiratory disease, congenital malformations, reproductive disorders and mucosal disease [9, 11–14].
BVDV belongs to the genus pestivirus with classical swine fever virus and border disease virus in the family Flaviviridae. The genome of the BVDV consists of a single positive-stranded RNA, which usually have a length of 12.3 kb . Two biotypes of BVDV categorized as cytopathogenic or noncytopathogenic based on their activity in cell culture have been recognized in the past years [16, 17]. Based on the basis of the nucleotide sequence of 5′-untranslated region (5′UTR), Npro or E2 gene, BVDV strains can be divided into two different genotypes, BVDV1 and BVDV2 . Each genotype can be further divided into different subgroups, and currently at least 11 genetic subgroups of BVDV1 and three genetic subgroups of BVDV2 are identified [3, 6, 18–24]. Recently, a new virus referred to as HoBi-like BVDV3 was identified in Europe, the virus can be divided into two sub-groups, Thai origin and Brazilian origin . BVDV1 spreads worldwide in cattle population [22, 23, 26, 27]. In the case of BVDV2 species, the highest occurrence is reported in the USA and Canada [25, 28], partially in Japan [29–31], Indian , South America , and occasionally in some European countries [6, 15, 32–35].
Virulence is both important to understanding the mechanisms of pathology and selecting the challenge strains for evaluation of a vaccine. Variation in virulence among BVDV2 strains has been extensively reported [36–38], but much less information is available on variation in virulence among BVDV1 strains. To date, the strain NY-1 has been used as a challenge strain for evaluating efficacy of vaccine protection against BVDV1. While it is well characterized, the clinical presentation infected with NY-1 indicates it is more likely a low virulence strain . So investigating an efficacious challenge virus to access the vaccine efficacy is very important.
To the present, many subgenotypes of BVDV1 have been isolated and detected in China [27, 40, 41]. Based on the phylogenetic tree, the clustering of BVDV1b and BVDV 1 m were the major prevalent subgenotypes in China [27, 41, 42]. However, BVDV subgenotype 1a was not isolated from cattle in China. Moreover, pathogenesis of above all strains was seldom reported.
In this study, one virus was isolated from nasal swabs of cattle using MDBK cell cultures, and identified as a BVDV isolate by the virus neutralization test, reverse transcriptase-polymerase chain reaction (RT-PCR) method and immunofluorescence assay. To investigate the genetic subgroup of the strain, the 5′UTR gene of the virus was sequenced and compared with other 13 reference BVDV strains by phylogenetic analysis. The pathogenesis of the virus was evaluated by intranasally inoculating to four susceptible calves to assess the potential endemic risk to the cattle herd in China.