The significance of the entomological surveillance in the prevention of vector-borne diseases

Abstract

Purpose: The aim of this presentation is to highlight the role of the entomological surveillance in the prevention of mosquito-borne diseases (MBD), using mainly, but not only, the long term mosquito-West Nile virus (WNV) monitoring in north-eastern Italy as a paradigmatic example. Going through the objectives of the entomological surveillance and using other targeted surveys we show how the results obtained were used to better target surveillance, to drive methods of mosquito control and risk communication and to prevent human transmission by modulating the screening of blood donors. Methods & Materials: Since 2010 an entomological monitoring was set up using CDC-CO2 traps and screening of mosquitoes by RT-PCR and sequencing for Flaviviruses. Other surveys included captures of mosquitoes every 2 hrs for 24 hrs, pre- and post-disinfestation captures, PCR blood meal analysis of fed Culex pipiens, retrospective analysis for other MBDs using stored mosquito DNA, and WNV complete genome. Results: Over 1 million of mosquitoes were collected in 158 sites, with Cx.pipiens the most abundant (88%) and the only vector of WNV and USUV. Tahyna, Marisma and mosquito-only Flaviviruses were isolated for the first time. The retrospective analysis on zoonotic filariae indicated the presence and distribution of Dirofilaria immitis and D.repens. Cx.pipiens fed preferentially on birds, mainly blackbird, magpie, sparrow and collared dove. Cx.pipiens changed its host searching activity according to the season, showing a night/evening peak in early/late summer, respectively. The disinfestation in rural areas did not reduce Cx.pipiens density. The entomological monitoring proved to early detect the viral circulation, before human cases. Conclusion: The entomological monitoring defined the risk areas for WNV. New viruses could also be detected. The blood-meal analyses indicated possible bird targets for surveillance. The determination of Cx.pipiens peak of activity defined the highest risk of human bite and WNV transmission. The control of the efficacy of disinfestations highlighted its poor efficacy in rural areas. The early detection of WNV in mosquitoes is now one of the triggers for the starting of WNV human blood screening, as stated by the National Integrated Surveillance and Control Plan for WNV and USUV, in a perfect One Health perspective.