ABSTRACT
Taxonomic classication based on molecular phylogeny. Sharing >84% nucleotide sequence identity, which was used for avivirus species denition based on partial NS5 gene tree, was a useful criterion for classifying POWV as a distinct species among tick-borne aviviruses [6]. More recently, it was found that all other tick-borne aviviruses (including POWV) could be similarly segregated into distinct species and subtypes using proportional amino acid distance (>0.45), based on complete ORF sequences as well; but, segregation based on NS3 gene sequences produced more discordant classication [7]. Using the above criteria, DTV designated for the virus strains isolated from northeastern parts of North America since 1995 [8] was classied as a subtype of POWV [6], as shown in the NS5 gene tree (Figure 21.1). A recent study revealed that all Russian strains belong to the genotype represented by the prototype (LB) strain [3]. Accordingly, POWV consists of two genotypes: the classic genotype represented by the prototype strain (LB) from Ontario, Canada as well as from northeastern United States and eastern Russia; and the DTV genotype isolated in Colorado and the northeastern and midwestern United States.
