**Acknowledgements**

The most of the viruses proliferate and form mature virus particles in sensitive cells in defi‐ nite temperature limits. A number of authors investigating the proliferation of TBEV strains in cell cultures at different temperatures (rct-feature) came to the conclusion that this marker could be the important phenotypical characteristics of the virus and closely connected with

We investigated rct42 genetic marker for 12 TBEV "group 886" strains. The results are pre‐

**37-42°С**

**rct42**

**Strain Isolaion source lgTCD50/ml at 37˚С lgTCD50/ml at 42˚С Difference**

636-90 *I. persulcatus* 4,78 5,78 -1,0 + 608-90 *I. persulcatus* 4,5 4,78 -0,28 + 606-90 *I. persulcatus* 4,0 6,83 -2,83 + 691-90 *I. persulcatus* 4,84 5,25 -0,41 + 418-90 *I. persulcatus* 4,0 3,0 1,0 + 740-84 *Myodes rufocanus* 7,18 6,95 0,23 + 712-89 *I. persulcatus* 4,0 2,23 1,77 + 733-90 *I. persulcatus* 4,25 5,57 - 1,32 + 742-90 *I. persulcatus* 3,5 3,0 0,5 + 711-84 *Myodes rufocanus* 8,26 5,90 2,36 ± 617-90 *I. persulcatus* 8,0 5,67 2,33 ± 886-84 *Myodes rutilus* 7,08 3,3 3,78 -

"Group 886" strains demonstrated the high heterogeneity in proliferation ability at 42°С. Five strains propagated more effectively at supraoptimal temperature (42º). Moreover, eight of nine strains isolated from ticks had rct42± feature. The strains isolated from rodents were more heterogenic: strain 740-84 had rct42+ feature, strain 886-84 had rct42- feature and strain 711-84 had rct42± feature. All TBEV "group 886" strains isolated from ticks collected in Kras‐

**1.** The new data concerning original TBE virus variant circulating on the territory of East‐ ern Siberia have been obtained. We have demonstrated the unique genetic structure of

its virulence [13, 14].

**Table 9.** Rct42 genetic marker for TBEV "group 886" strains.

**4. Conclusions**

nochikoiskiy district of Transbaikalia actively propagate at 42ºС.

sented in Table 9.

108 Encephalitis

The authors are greatly appreciated to all colleagues collected the field materials and to the staff of Natural-Foci Infection Department: E.V. Arbatskaya, I.V. Voronko, O.Z. Gorin, N.A. Gusarova, G.A. Danchinova, V.M. Kogan, S.I. Lipin, O.V. Melnikova, A.G. Trukhina. Also we acknowledge the partial financial support by Integration interdisciplinary project grant No. 135 from the Siberian Branch of the Russian Academy of Sciences.
