Background. During the study of the genetic variability of the tick-borne encephalitis virus (TBEV) in Eastern Siberia, a group of 22 strains with a unique genetic structure significantly different from all known TBEV subtypes was identified. This TBEV variant was tentatively called “group 886”. Therefore, for this original TBEV variant it was necessary to study the genetic, biological properties of the “group 886” strains, clarify its TBEV taxonomic status, its range, evolutionary history, etc.Aim. The generalization of the currently available data on genetic and biological properties of TBEV “886” group.Materials and methods. The genetic structure of “group 886” strains was studied by the complex of molecular-genetic methods (MHNA, sequencing of fragments or the complete genome).Results. It was shown that “group 886” strains form a separate cluster on phylogenetic tree, and the level of genetic differences from other genotypes is more than 12 %. It was defined that this TBEV variant has its own area (Irkutsk region, Republic of Buryatia, Trans-Baikal region, Northern Mongolia). Its ecological connection with all links of the transmissive chain (ixodid ticks, small mammals, human), participation in human pathology, stability and duration of circulation in the Baikal region, individual evolutionary history were proved. Some phenotypic characteristics of the “group 886” strains were considered.Conclusion. The presented data testify to the validity of the “886 group” isolation as an independent genetic type. Taking into account the geographical distribution of this TBEV genotype, we propose to assign it the name “Baikal genotype/subtype”.

Tick-borne encephalitis virus (TBEV) is the most important tick-transmitted arbovirus causing human disease in Europe and Asia. Over the past decades, the incidence of TBEV infection has significantly increased, with over 13,000 annual hospital referrals in endemic countries and cases emerging in previously unaffected regions. Specific detection of TBEV is required to diagnose suspected human cases or during surveillance of tick vectors and/or susceptible animal species. Widely used techniques for diagnosis comprise serological methods to detect viral antigens or antibodies and nucleic acid tests to detect viral RNA in target specimens. Moreover, virus isolation using susceptible cell lines or vertebrates, electron microscopy, or immunohistochemistry can also be employed on specific occasions. The purpose of this review is to compile and outline various approaches and techniques for detecting TBEV infection in ticks, wild animals, and humans. Specific sections for specimen collection and storage, nucleic acid testing, and serological assays cover various aspects of dynamics, performance characteristics, and utility in the diagnostic workup of suspected cases. Impact of immunoglobulin M testing and quantification, immunoglobulin G avidity, and real-time and quantitative polymerase chain reaction methods were overviewed with assay comparisons. Recent advances in serological assays to mitigate the impact of cross-reactions were further discussed along with the detailed interpretation of laboratory test results in human infections.