Results of reconnaissance epizootiological monitoring for West Nile fever in certain regions of European Russia and the Urals in 2024

Introduction. Climate warming contributes to the intensification of epizootic and epidemic processes of West Nile fever (WNF). In southern Russia, the activity of the epizootic process is recorded annually, but in the central region of the European part of the country and in the Urals, the enzootic circulation of the West Nile virus (WNV) has not been confirmed in the territory of 20 subjects. The aim of the study is to investigate zoological and entomological material for WNV infection to confirm the ongoing epizootic process in old WNV foci and in previously non-endemic areas. Materials and methods. Field samples were collected in 2024 in 19 subjects in accordance with the methods regulated in normative documents. The material was studied using the reverse transcription polymerase chain reaction method. Results. In total, during the 2024 field season, 5,419 samples of field samples were examined: 684 samples of birds from 74 species, 455 samples of small mammals from 13 species, 45 samples of frogs from 1 species, 3,665 samples of blood-sucking mosquitoes from 33 species (93,438 specimens), and 570 samples of ixodid ticks from 17 species (4,809 specimens). Markers of WNV in field samples were detected in 7 subjects from 3 federal districts. In the Kirov and Chelyabinsk regions and the Republic of Mordovia, evidence of the ongoing epizootic process of WNF has been obtained for the first time. WNV RNA was detected in 6 (0.5%) out of 1184 tested samples of vertebrate animals and in 27 (0.6%) out of 4235 samples of arthropods. The level of individual infection was 0.03% in blood-sucking mosquitoes, 0.06% in ixodid ticks, and 0.9% in birds. Conclusion. The results of the studies confirm the enzootic circulation of WNV in the territories of the Southern, Volga and Ural Federal Districts.