Distribution of the tick-borne encephalitis virus among naturally infected ixodid ticks and small mammals in the Novosibirsk region

A comparative analysis of the virus infection carrier state and distribution of genetic types of the virus of tick-borne encephalitis (TBE) among invertebrates (2 species of ticks, Ixodes persulcatus Schulze and Ixodes pavlovskyi Pomerantsev 1946) and vertebrate reservoir hosts (4 species of small rodents: the red vole Myodes rutilus Pallas, gray-sided vole Myodes rufocanus Sundevall, field mouse Apodemus agrarius Pallas, birch mice Sicista betulina Pallas and 1 species of insectivores - common shrew Sorex araneus L (1758)), dominating on the territory of the Novosibirsk region in 2009-14 years, was performed with the use of virological and molecular biological methods. Frequency detection of RNA and / or E protein in mammals (70,9 ± 3,0%) were shown to considerably exceed levels of virus infection carrier state rate of ticks (3,4 ± 0,4). In the circulation of three major types of TBE - Far East (FE), Siberian (NIB) and European (Eur) in natural populations in mono - or polytype forms in mites Sib type prevailed (p <0,01), in small mammals - ET type (p <0.001). At the same time the number of genome equivalents FE type in average accounted for 3.2 • 10 4 copies in the mite; Sib and Eur - about 10 and 100 times lower, respectively. In the blood of wild rodents, the amount of RNA ofFE of type TBEV ranged from 2.4 • 10 5 mL, of Sib type - 2.4 • 10 2. With account of blood volume of mammals consumed by larvae and nymphs, the falling of several hundreds and thousands of viral genomes such as DV and only single type of RNA Sib IRB, respectively, is possible in the tick. Passaging TBE isolates from wild reservoir hosts in laboratory mice lead to the transformation of the original genetic composition. In minimal genetic rearrangements ofpathogenic isolates of TBE in infected mice-suckers the transformation of apathogenic isolates was significant. The polytype composition of natural populations of TBE should be considered in the development of diagnostic and preventive preparations.

flavivirus, molecular typing, reverse transcription followed by real-time PCR with genotype-specific probes, phylogenetic analysis, adaptation to the reservoir hosts