Heterogeneity of 3'-Untraslated Region of Genome RNA of the Tick-Borne Encephalitis Virus (TBEV) Strains Isolated from Ticks in the Western Siberia, Russia.

The tick-borne encephalitis virus (TBEV) strains have been isolated from unfed adult ticks Ixodes persulcatus Schulze in Novosibirsk region (South-Western Siberia, Russia) beginning from 1980 till 2006. The TBEV 3'-untraslated region (3'UTR) variable fragment was amplified with primers corresponding to conserved flanking areas. The RT-PCR product lengths varied in range from 100 to 400 bp. Comparative analysis of 3'UTR nucleotide sequences revealed a few groups of the TBEV strains within Siberian genetic subtype with significant intra-group homology and essential differences between groups. Correlation between lengths of the 3'UTR fragments and hemagglutination (HA) titers for subsequent passages of the TBEV strains was not found. However, for the viral strains with shorter 3'UTR (less than 200 nucleotides) incubation period for suckling mice was longer than 5 days. It might be resulted from decreased RNA synthesis or reduced neuroinvasiveness.