Mel'nikova Ol'ga V, Adel'shin R V, Korzun V M, Trushina Yu N, Andaev E I
Vopr Virusol. 2016;61(5):229-34.
The Irkutsk region is the unique territory where all known subtypes of tick-borne encephalitis virus (TBEV) circulate. In the last years, the phenomenon of changes in TBEV subtypes (substitution of the Far-Eastern subtype by the Siberian one) was noted in some regions of the Russian Federation. The results of individual investigation of 11522 Ixodes persulcatus ticks and brain specimens from 81 small mammals collected in natural foci of the Irkutsk region during 2006-2014 are presented in the article. More than 60 TBEV strains have been isolated and studied by virological methods; E gene fragments (1193 b.p.) of 68 isolates have been typed. The majority of the strains (irrespective of subtype) were of high virulence for laboratory mice (LM) in case of both intracerebral and subcutaneous inoculation of virus. All isolates from warm-blooded small mammals and humans were of high virulence for LM, but placed in the same clusters of the phylogenetic tree with ticks collected in the same area. Tick-borne strains of different virulence also did not form separate clusters on the tree. Phylogenetic analysis showed that modern TBEV genotypic landscape of the studied territory is changing toward absolute predominance of the Siberian subtype (94.1%). This subtype is represented by two groups with prototype strains “Zausaev” and “Vasilchenko”. The “Vasilchenko” group of strains is spread on the whole territory under study; the strains of “Zausaev” group were isolated previously in the Irkutsk suburbs. The European subtype of TBEV circulates in natural foci of Pribaikalie permanently (at least 5% of the random sampling); the strains are of high virulence for LM. The Far-Eastern TBEV subtype was not found within the group of isolates collected in 20062014. The phylogenetic relationship of the strains under study had a higher correlation with the place of isolation than with the year or source.
伊尔库茨克地区是蜱传脑炎病毒（TBEV）所有已知亚型都在其中传播的独特区域。近年来，在俄罗斯联邦的一些地区注意到了TBEV亚型变化的现象（远东亚型被西伯利亚亚型取代）。本文介绍了2006 - 2014年期间在伊尔库茨克地区自然疫源地采集的11522只全沟硬蜱和81只小型哺乳动物脑标本的个体调查结果。已通过病毒学方法分离并研究了60多种TBEV毒株；对68株分离株的E基因片段（1193个碱基对）进行了分型。大多数毒株（无论亚型如何）在脑内和皮下接种病毒时对实验室小鼠（LM）具有高毒力。来自温血小型哺乳动物和人类的所有分离株对LM都具有高毒力，但在系统发育树中与在同一地区采集的蜱处于同一簇。不同毒力的蜱传毒株在树上也未形成单独的簇。系统发育分析表明，研究区域的现代TBEV基因型格局正朝着西伯利亚亚型的绝对优势（94.1%）转变。该亚型由具有原型毒株“扎萨耶夫”和“瓦西里琴科”的两组代表。“瓦西里琴科”组毒株分布在整个研究区域；“扎萨耶夫”组毒株先前在伊尔库茨克郊区被分离出来。TBEV的欧洲亚型在贝加尔湖沿岸地区的自然疫源地持续传播（至少占随机抽样的5%）；这些毒株对LM具有高毒力。在2006 - 2014年收集的分离株组中未发现远东TBEV亚型。所研究毒株的系统发育关系与分离地点的相关性高于与年份或来源的相关性。
