Distribution and characterization of tick-borne encephalitis viruses from Siberia and far-eastern Asia

In this study, tick-borne encephalitis (TBE) viruses from Siberia and far-eastern Asia were characterized in order to determine virus subtype distribution. TEE viruses were isolated from ticks (Ixodes persulcatus) collected in the far-eastern (Khabarovsk and Vladivostok) and Siberian (Irkutsk) regions of Russia in 1999. Phylogenetic analysis showed that isolates formed distinct clusters of far-eastern and Siberian subtypes, There was also a minor difference in antigenicity between the Irkutsk isolates and other TEE virus strains, as demonstrated by the reactivity of monoclonal antibodies. Amino acid alignments of the E gene showed that the Irkutsk isolates had a single amino acid change at position 234 (Q or H); this amino acid position is considered to be a 'signature' of Siberian subtype TEE viruses. Strains isolated in Irkutsk also exhibited equivalent or somewhat higher virulence in mice compared with far-eastern TEE virus isolates. All viruses isolated in this study (i.e. far-east Asian and Siberian isolates) have 3 ' non-coding regions (NCRs) of almost the same length, which contrasts with the various sizes of 3 ' NCRs of other TEE viruses strains reported previously. The data presented in this study show that the 3 ' NCR is uniform among TEE viruses isolated from Siberia and far-eastern Asia and that the 3 ' NCR is essential for TEE virus growth in tick and/or rodent host cells.