Nucleotide sequencing and phylogenetic analysis of 17 Brazilian isolates of bovine viral diarrhea virus (BVDV) identified four isolates (23.5%) belonging to genotype 1a (BVDV-1a), nine isolates (52.9%) of the genotype 1b (BVDV-1b) and four isolates (23.5%) belonging to genotype 2 (BVDV-2). The Brazilian BVDV type 2 isolates were shown to be genotypically different from the BVDV type 2 identified so far in North America and Europe, suggesting they might belong to a new subgenotype. Antigenic characterization of these isolates by cross-neutralization revealed a very low serologic cross-reactivity with vaccine BVDV strains. The immune serum raised in lambs to three vaccine strains presented a very low and even negligible neutralizing activity against some Brazilian BVDV type 1 and 2 isolates. Up to 128-fold differences in serum neutralizing antibody titers were observed between the vaccine strains and some Brazilian BVDV isolates. The potential impact of the antigenic variability of BVDV on serologic diagnosis was investigated by testing field serum samples by serum-neutralization (SN) against viruses of both genotypes. Two hundred and eighty samples (24.7%) had neutralizing antibodies against BVDV. Out of these, 215 (76.8%) had neutralizing activity against viruses of both genotypes, 37 samples (13.2%) reacted only against BVDV type 2 and 28 (10%) were positive only to BVDV type 1. These results demonstrate that SN tests using only one virus may result in a significant number of false-negative results. The reduced neutralizing activity of the antisera to vaccine strains against some Brazilian isolates raises the question about the degree of protection conferred by these vaccines and indicates the need of producing vaccines based on local viruses and/or including viruses of both genotypes.
Bovine viral diarrhea virus; BVDV; antigenic diversity; vaccine; genotype
