We report the isolation and detailed characterization of the novel strain, Partizansk/2006, of Powassan virus (POWV) from a human case of infection, which occurred in Primorsky krai, Russia, in 2006. Comparative complete genome sequence analysis of the Far Eastern strains Spassk-9 (1975), Nadezdinsk-1991 and Partizansk/2006 of POWV revealed that these strains are 99.8% similar to the LB strain, which was isolated in Canada in 1958. Phylogenetic analysis of 5' UTR sequences of five other strains of POWV isolated from 1972 to 1986 in Primorsky krai produced similar results. Presumably, Far Eastern POWV has common putative ancestor with LB strain POWV from North America, and the time of divergence of these POWVs is relatively short. We conclude that POWV has become endemic in Far Eastern Russia.
We report the prevalence of Siberian and Far Eastern subtypes of tick-borne encephalitis virus (TBEV) in Ixodes persulcatus and Ix. pavlovskyi ticks collected in Tomsk and its suburbs during 2006-2008. The TBEV was detected in 5.7% ticks collected in the city, where Ix. pavlovskyi ticks were dominated and 7.5% ticks from suburban foci with prevalence Ix. persulcatus ticks. Genotyping of the virus showed that Siberian subtype (89.5%) is predominant in individual ticks of Tomsk suburbs; however, the proportion of Far Eastern subtype in two urban sites reached 47%. Phylogenetic analysis demonstrated that Siberian subtype variants from individual ticks were quite divergent and original. Only one subclade was found to be similar to Zausaev strain of TBEV, which is the etiological agent of lethal chronic form of tick-borne encephalitis infection. The average level of homology of 5' noncoding region (5'-NCR) of TBEV in the individual ticks was 95% for Far Eastern subtype and 89% for Siberian subtype of TBEV. Multiple substitutions in 5'-NCR were found in viral RNA derived from individual ticks. The A2 and C1 elements of Y-shaped structure and putative site for viral RNA polymerase were most variable regions for TBEV 5'-NCR. The B1 and B2 elements and the start codon were practically conserved. The viral RNA from three TBEV-infected pig kidney embryo cells after three passages (out of 21 polymerase chain reaction-positive ticks) were found to multiple substitutions in 5'-NCR in comparison with viral RNA from individual parent tick. However, these three variants did not replicate efficiently in pig kidney embryo cells that may be connected with a considerable modification of Y-shaped structure of 5'-NCR. The efficiently replicating isolate Kolarovo had only seven substitutions in the 5'-NCR and typical Y-shaped structure for Siberian subtype of TBEV. Our data support the idea that hypervariability of the 5'-NCR reflects viral strategy to select the fittest RNA molecule for productive viral infection in mammalian and tick cells.
We isolated a novel strain of tickborne encephalitis virus (TBEV), Glubinnoe/2004, from a patient with a fatal case in Russia. We sequenced the strain, whose landmark features included 57 amino acid substitutions and 5 modified cleavage sites. Phylogenetically, Glubinnoe/2004 is a novel variant that belongs to the Eastern type of TBEV.
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