Immunodominant E2 (gp53) sequences of highly virulent bovine viral diarrhea group II viruses indicate a close resemblance to a subgroup of border disease viruses.

The genes for the E2 envelope protein, which elicits virus-neutralizing antibodies, from members of the newly described group II of bovine viral diarrhea viruses (BVDVs) were cloned and sequenced. These BVDVs included a thrombocytopenic strain from the United States, a fetal bovine serum contaminant, a strain from Western Canada, and two highly virulent strains, causing high mortality rates, from Quebec. The nucleotide and amino acid sequences of these E2s had only a 60-65% homology with group I BVDV E2s but >90% homology with the E2 of a subgroup of sheep border disease viruses. The E2 gene of the NADL strain was expressed and monospecific antibodies were raised in calves and rabbits. The virus-neutralizing titers of these antisera were 15- to 80-fold lower for the heterologous group of BVDVs as compared to those for the homologous BVDVs.