SEQUENCE VARIATION OF THE GLYCOPROTEIN GENE IDENTIFIES 3 DISTINCT LINEAGES WITHIN FIELD ISOLATES OF VIRAL HEMORRHAGIC SEPTICEMIA VIRUS, A FISH RHABDOVIRUS

To evaluate the genetic diversity of viral haemorrhagic septicaemia vi rus (VHSV), the sequence of the glycoprotein genes (G) of 11 North Ame rican and European isolates were determined, Comparison with the G pro tein of representative members of the family Rhabdoviridae suggested t hat VHSV was a different virus species from infectious haemorrhagic ne crosis virus (IHNV) and Hirame rhabdovirus (HIRRV), At a higher taxono mic level, VHSV, IHNV and HIRRV formed a group which was genetically c losest to the genus Lyssavirus. Compared with each other, the G genes of VHSV displayed a dissimilar overall genetic diversity which correla ted with differences in geographical origin, The multiple sequence ali gnment of the complete G protein, showed that the divergent positions were not uniformly distributed along the sequence, A central region (a mino acid position 245-300) accumulated substitutions and appeared to be highly variable, The genetic heterogeneity within a single isolate was high, with an apparent internal mutation frequency of 1.2 x 10(-3) per nucleotide site, attesting the quasispecies nature of the viral p opulation, The phylogeny separated VHSV strains according to the major geographical area of isolation: genotype I for continental Europe, ge notype II for the British Isles, and genotype III for North America, I solates from continental Europe exhibited the highest genetic variabil ity, with sub-groups correlated partially with the serological classif ication, Neither neutralizing polyclonal sera, nor monoclonal antibodi es, were able to discriminate between the genotypes, The overall struc ture of the phylogenetic tree suggests that VHSV genetic diversity and evolution fit within the model of random change and positive selectio n operating on quasispecies.