European subtype of tick-borne encephalitis virus. Literature review

Abstract

This review is devoted to the European subtype of tick-borne encephalitis virus (TBEV). It summarizes and analyzes the information available at the scientific literature on the genetic and biological properties of strains of this virus subtype. A comparative analysis of the complete coding sequences of all currently recognized tick-borne flaviviruses was carried out. It was noted that the differences in TBEV strains included in the European subtype are minimal, which indicates a higher degree of their genetic homogeneity than in strains of the Far Eastern and Siberian subtypes. The level of differences in the genome of strains of the European subtype, depending on the region and the source of isolation, was analyzed. No relationship was found between the level of homology of nucleotide sequences of TBEV strains of the European subtype and the source of isolation. The proposed models for the evolution of TBE are described. The area of TBE of the European subtype in Eurasia is analyzed. The maps of the geographical distribution of the European subtype are presented. It shows the European subtype TBE is found in 14 regions of Russia. TBE of this subtype, as a rule, causes a disease with a milder course in comparison with TBE caused by a virus of the Far Eastern or Siberian subtypes. An analysis of the main vectors and reservoir hosts of the European subtype TBEV in Europe and in Siberia has been carried out. It is emphasized that in Eurasia the European TBEV circulates in territories that differ significantly in climatic conditions, relief, landscape, and characteristics of biotopes. However, analysis of scientific literature data showed that, despite these differences, it has a high degree of genome stability.