PHYLOGENY OF THE GENUS FLAVIVIRUS

We undertook a comprehensive phylogenetic study to establish the genet ic relationship among the viruses of the genus Flavivirus and to compa re the classification based on molecular phylogeny,vith the existing s erologic method. By using a combination of quantitative definitions (b ootstrap support level and the pairwise nucleotide sequence identity), the viruses could be classified into clusters, clades, and species. O ur phylogenetic study revealed for the first time that from the putati ve ancestor two branches, non-vector and vector-borne virus clusters, evolved and from the latter cluster emerged tick-borne and mosquito-bo rne virus clusters. Provided that the theory of arthropod association being an acquired trait was correct, pairwise nucleotide sequence iden tity among these three clusters provided supporting data for a possibi lity that the non-vector cluster evolved first, followed by the separa tion of tick-borne and mosquito-borne virus clusters in that order. Cl ades established in our study correlated significantly with existing a ntigenic complexes. We also resolved many of the past taxonomic proble ms by establishing phylogenetic relationships of the antigenically unc lassified viruses,vith the well-established viruses and by identifying synonymous viruses.