**1. Introduction**

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In the XXI century tick-borne encephalitis (TBE) remains the most distributed severe natural foci infection transmitted by Ixodes ticks bite.

The causative agent of this infection is tick-borne encephalitis virus (TBEV). According to the modern classification it belongs to the group of mammal viruses transmitted by ticks, and is a member of the genus Flavivirus of the family Flaviviridae [23]. As a result of nu‐ merous studies devoted to TBEV genetic variability it was divided into three genotypes (subtypes): 1) genotype 1 (Far-Eastern (FE) subtype); 2) genotype 2 (European subtype); 3) genotype 3 (Siberian subtype). Each genotype is believed to distribute in its certain area where its absolute domination is observed [10, 20].

In Eastern Siberia the circulation of three TBE virus genotypes with the domination of geno‐ type 3 was identified by the prior study. Moreover, the unique TBEV strains (886-84 and 178-79), which differed in genetic structure from all known TBEV genotypes, have been found on this territory [10].

Currently, with use of molecular hybridization of nucleic acids (MHNA) method with geno‐ type-specific probes and sequencing of complete virus genome or its fragments we identi‐ fied the group of 13 strains with high homology level to 886-84 strain that was

conventionally defined as "group 886" [6]. The obtained results confirm the validity of "group 886" certification as possible separate TBEV genotype.

**2.2. Strains genotyping**

formed by the common methods [16].

**2.3. Strains immunotyping**

**2.4. Neuroinvasiveness**

1 Tissue cytopathogenic dose

We used MHNA with three panels of 40 deoxyoligonucleic probes complemented to frag‐ ments of 10 genes of different TBEV genotypes. The probe description and their localization

Genetic and Biological Properties of Original TBEV Strains Group Circulating in Eastern Siberia

http://dx.doi.org/10.5772/54087

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The total RNA extraction from infected mice brains or porcine embryo kidney cells, apply‐ ing RNA onto kapron or cellulose nitrate filters and hybridization with probes were per‐

The amplification was carried out with primers complemented to 5'- UTR fragment, to CprM-E-NS1 genes, E gene or E-NS1 genes fragments, synthesized in the Institute of Chemi‐ cal Biology and Fundamental Medicine SB RAS (Novosibirsk, Russia). RT-PCR was

The sequence analysis of PCR products was carried out with BigDye Terminators Cycle Se‐ quencing Kit v.3.1 (Applied Biosystems, USA) in DNA Sequencing Center SB RAS, Novosi‐ birsk, Russia. The obtained data was analyzed by Mega 5.0 program [28]. The gene fragments sequences of TBEV strains belonging to the different genetic types from GenBank database were used as a material for comparison. BLAST program (http:// www.ncbi.nlm.nih.gov/blast/) was used for homology search of obtained nucleotide sequen‐

The genome fragments sequences of "group 866" strains obtained during the study have been deposited into GenBank database with access numbers EF469662, EU878281-EU878283,

The sequencing of full genome of 886-84 strain has been performed by Karan *et al*. in Central

The reaction of diffuse precipitation in agar (RDPA) was carried out by the method developed by Clark [12] with modifications by Rubin [27] and Bochkova [2]. We used immune sera against TBEV prototype strains of three serotypes (Sofjin – Far-Eastern serotype, 256 – Western sero‐ type, Lesopark-11 and Aina/1448 – East-Siberian serotype) exposed to dosed adsorbtion with

The cytoplasmatic activity study was performed according to common methods. Virus titers were determined in tests on cell culture based on its cytopathic activity (CPA) by the full

To estimate the neuroinvasiveness of TBEV strains we determined the index of invasiveness (II) – the difference between the virus titers after intracerebral (mNic) and subcutaneous

/ml [26].

concentrated cultural antigens or cross-adsorbed sera against investigated strains [4].

cumulative method (offered by Reed and Muench) and expressed as lg TCD50 <sup>1</sup>

Research Institute of Epidemiology of Rospotrebnadzor RF, Moscow, Russia.

performed according to the "BioSan" company (Novosibirsk, Russia) protocol.

in TBEV genome was presented earlier by Demina *et al*. [6].

ces with already known fragments of TBEV genomes.

JN936341, JN936347, JN936349-JN936350, JN936353-JN936355.

The unique genetic structure of "group 886" strains also manifests in original phenotype pattern that is quite significant from the scientific point of view. "Group 886" strains can be tested as prototype candidate strains for the design of universal vaccines effective against strains of different serotypes (genotypes) and TBEV test-systems.

The aim of the study was to investigate genetic and biological properties of TBEV "886 group" strains circulating in Eastern Siberia (territories of Irkutsk region, Buryat Repub‐ lic, Transbaikalia) for estimation of their potential as candidates for test-systems and vac‐ cine development.
