Selection of Monitoring points for the Number and Infectivity of the Main Vectors of West Nile Virus in the Volgograd Region

Abstract

Relevance. Since 1999, the incidence of West Nile fever has been recorded in the Volgograd region. The main vectors of West Nile virus in Russia are Cx mosquitoes. pipiens L. and Cx. modestus Fic. An objective assessment of the entomological situation and infection rate of these species within the framework of epidemiological surveillance of West Nile fever is possible only in biotopes with sufficiently high numbers of mosquitoes; therefore, the choice of sampling points is an urgent task. Purpose of the study. Analysis of the West Nile virus main vectors - mosquitoes Cx. pipiens L. and Cx. modestus Fic. average number, occurrence and infection rate at the various open biotopes of the Volgograd region to justify the choice of optimal points for entomological monitoring. Materials and methods. The catching and accounting of the mosquitoes’ number was carried out in 2015–2019 from May to August in the third decade of each month in a floodplain forest, at a personal plot, a summer cottage and on bank of water body. To catch mosquitoes, automatic traps Mosquito Magnet Executive and LovKom-1 were used. The accounting unit was the number of mosquitoes collected in both traps per trap-night. The average number, the index of occurrence and infection rate were determined by generally accepted methods. Detection of West Nile virus RNA in samples of mosquito pool suspensions was performed by RT-PCR using the AmpliSense WNV-FL reagent kit. The results were statistically processed using Microsoft Excel 2016 (Microsoft Corporation, USA). Results. In the 2015-2019 period, 17468 mosquitoes of the genus Culex: 8258 species – Cx. pipiens L., 9210 species – Cx. modestus Fic. were collected in over than 80 trap nights at the selected stationary points of the Volgograd region. Average number of Cx. pipiens L. was: in the floodplain forest – 4.6 individuals per 1 trap-night; at the personal plot – 183.9; at the summer cottage – 30.2; on the bank of water body – 194.3. Average number of Cx. modestus Fic. was: in the floodplain forest – 5.2 individuals per 1 trapnight; at the personal plot – 8.3; at the summer cottage – 2.5;on the bank of water body – 444.6. Occurrence index Cx. pipiens L. was highon the bank of water body and at the personal plot (47.1% and 44.5%, respectively), much lower – at the summer cottage (7.3%) and in the floodplain forest (1.1%). Level of WNV infection among Cx. pipiens L.on a personal plot was 5.4%, on a summer cottage – 3.6%,on the bank of water body – 2.2%. No infected samples were found among Cx. pipiens L. collected from the floodplain forest. WNV RNA in samples from mosquitoes Cx. modestus Fic. found only in individuals caughton the bank of water body. Their infection rate was 1.2%. Discussion. Ecological plasticity of Cx. pipiens L. mosquitoes allows them to live in settlements and near water bodies. Mosquitoes of the species Cx. modestus Fic. do not fly away from ponds, breeding places. Conclusion. High numbers and occurrence of the Cx. pipiens L. mosquitoes were observed at a personal plot within the city andon the bank of water body, Cx. modestus Fic. –on the bank of water body. WNV RNA positive samples were detected from mosquitoes collected at the personal plot, the summer cottage andon the bank of water body. To monitor the number and infection rate among Cx. pipiens L., points of registration and sampling should be placed in open stationson personal plots in settlements, banks of water bodies and summer cottages. We recommend to carry entomological monitoring for Cx. modestus Fic. out onlyon the banks of water bodies along the water's edge in reed thickets. The placement of the main WNV vectors number and infection rate monitoring points in the floodplain forest is not advisable.