| Abstract: | Flaviviruses from a tick-borne encephalitis virus (TBEV) complex circulate in about all the countries widely distributed in Northern Eurasia. Complete nucleotide sequences for genomes of different 15 tick-borne encephalitis viruses have been determined in the past years. Phylogenetic analyses of these sequences showed their significant genetic variability. Thus, the genetic differences in the genomes of TBEV strains are as high as 17.3%, but the differences in the amino acid sequences are 9%. These genetic differences permit determination of the time of divergence of the current TBEV genovariants from the common viral precursor in 1700 to 2100. Novel genetic variants of the Far-Eastern TBEV subtype, which are represented by Senzhang and Glubinnoe/2004 viruses, have been discovered in the pastyears. New variants of the same Far-Eastern subtype of TBEV, which are able to induce hemorrhagic tick-borne encephalitis, have been found in Western Siberia. The fact that there are considerable genetic differences in Turkish and Spanish sheep encephalitis viruses has been established within the European subtype of TBEV. The Siberian subtype of TBEV is genetically more uniform; however co-circulation of the Far-Eastern and Siberian subtypes of TBEV has been found in the natural TBEV foci of Siberia. This suggests that there may be at present a change in the genotypes of TBEV in different geographical regions. |
