| Bovine viral diarrheal virus (BVDV), the causal agent of BVD and mucosal disease complex, is classified in the genus Pestivirus in the family Flaviviridae. Although cattle are the primary host for BVDV, several reports suggest most even-toed ungulates are also susceptible. Based on comparisons of nucleotide sequence in the viral RNA, there are at least 2 viral genotypes (distinct genetic groups) of BVDV that can be further divided into subgenotypes or genogroups. The viral genotypes are termed BVDV type 1 and BVDV type 2, and both cytopathic and noncytopathic BVDV are represented in each viral genotype. The subgenotypes are clusters of viruses within a viral genotype that are highly similar in nucleotide sequence of the viral RNA. (Subgenotypes are designated by lower case letters; thus, subgenotypes of genotype 1 BVDV would be represented as 1a, 1b, 1c, etc.) Currently, the number of viral subgenotypes remains unknown. Based on sequence of several hundred nucleotides of select regions of viral RNA, type 1 BVDV has at least 12–15 subgenotypes and type 2 BVDV has at least 2 subgenotypes (Merck Vet Manual: Bovine Viral Diarrhea). |
