Genetic and antigenic analysis of the G attachment protein of bovine respiratory syncytial virus strains

Antigenic and genetic studies of bovine respiratory syncytial virus (BRSV) were made on isolates obtained from three continents over 27 years. Antigenic variation between eight isolates was initially determined using protein G-specific monoclonal antibodies. Four distinct reaction patterns were observed, two of which corresponded to the previously established subgroups A and AB. A third pattern was produced by five Scandinavian strains and a fourth was observed from a single Dutch isolate. The genetic diversity of 27 strains of BRSV was investigated by comparative nucleotide sequence analysis of a 731 nucleotide fragment in the G protein gene. Nine of the BRSV strains were analysed by direct sequencing of RT-PCR amplicons whereas sequences of 18 BRSV and three human respiratory syncytial virus (HRSV) strains were obtained from GenBank. The analysis revealed similarities of 88-100% among BRSV strains and 38-41 % between BRSV and HRSV. A phylogenetic tree created for BRSV revealed two main branches, one of which divided into five further lineages, each representing a geographic cluster. A correlation was evident between the positions of some strains in the phylogenetic tree and their antigenic pattern. For HRSV strains, a genetic similarity of only 62% allowed the distinction of two antigenic subgroups, A and B, a pattern which was not seen for BRSV. This study showed that genetic analysis was an accurate method for discriminating BRSV strains and that these viruses should be regarded as a single genetic and antigenic group, within which variants can be distinguished.