Study of the circulation and properties of the West Nile virus in Russia in 2022

Abstract

Introduction. The relevance of the study is due to the need to assess the real expansion of West Nile fever (WNF) in Russia, analyze the manifestations of epizootic and epidemic processes and study the population structure of West Nile virus (WNV). Aim. To obtain objective data on the intensity of WNV circulation in certain territories of Russia and study the properties of the isolated strains of the pathogen. Materials and methods. 4564 samples of field material from 23 subjects of the Russian Federation and 1547 samples of clinical material from 12 subjects of the Russian Federation were examined. A set of laboratory diagnostic methods was used: ELISA, RT-PCR, virological, sequencing. Results. In 20 out of 1331 (1.5%) examined febrile patients, IgM antibodies to WNV were detected, including positive cases identified for the first time in the Karachay-Cherkess Republic, Tver and Vladimir regions. The presence of immunity to WNV was found on average in 8.6% of 11 federal subjects' population with high seroprevalence rates in Zaporozhye (24,5%), Tula (15,4%) and Kursk (11,1%) regions. Low-avidity IgG antibodies were detected in 44 (33,1%) samples from a population of 9 federal subjects. Intensive circulation of WNV lineage 2 in the epizootic cycle in the southern part of European Russia was confirmed. 12 WNV isolates were obtained, including those isolated for the first time in the Republic of Crimea, the Karachay-Cherkess Republic and the Stavropol Territory. The heterogeneity of circulating WNF causative agent's strains related to the two clades of the WNV lineage 2 formed in 2021 and 2022 was established. Conclusion. In the course of comprehensive monitoring studies, a new northern border of the WNF range was established, which as of 2022 passes through the territory of the Tver region. Data from seroepidemiological studies, including the detection of low-avidity IgG antibodies, confirm fairly intense, but undiagnosed contact of the population of the European part of Russia with the WNF pathogen. In the southern region of the European part of Russia, WNV genotype 2 predominantly circulates, belonging to at least two clades formed in 2021 and 2022.