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West Nile Virus: High Transmission Rate in North-Western European Mosquitoes Indicates Its Epidemic Potential and Warrants Increased Surveillance

Abstract : Background West Nile virus (WNV) is a highly pathogenic flavivirus transmitted by Culex spp. mosqui- toes. In North America (NA), lineage 1 WNV caused the largest outbreak of neuroinvasive disease to date, while a novel pathogenic lineage 2 strain circulates in southern Europe. To estimate WNV lineage 2 epidemic potential it is paramount to know if mosquitoes from cur- rently WNV-free areas can support further spread of this epidemic. Methodology/Principal Findings We assessed WNV vector competence of Culex pipiens mosquitoes originating from north-western Europe (NWE) in direct comparison with those from NA. We exposed mos- quitoes to infectious blood meals of lineage 1 or 2 WNV and determined the infection and transmission rates. We explored reasons for vector competence differences by comparing intrathoracic injection versus blood meal infection, and we investigated the influence of temperature. We found that NWE mosquitoes are highly competent for both WNV lineages, with transmission rates up to 25%. Compared to NA mosquitoes, transmission rates for line- age 2 WNV were significantly elevated in NWE mosquitoes due to better virus dissemina- tion from the midgut and a shorter extrinsic incubation time. WNV infection rates further increased with temperature increase. Conclusions/Significance Our study provides experimental evidence to indicate markedly different risk levels between both continents for lineage 2 WNV transmission and suggests a degree of genotype-geno- type specificity in the interaction between virus and vector. Our experiments with varying temperatures explain the current localized WNV activity in southern Europe, yet imply fur- ther epidemic spread throughout NWE during periods with favourable climatic conditions. This emphasizes the need for intensified surveillance of virus activity in current WNV dis- ease-free regions and warrants increased awareness in clinics throughout Europe.
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Jelke Fros, Corinne Geertsema, Chantal Vogels, Peter Roosjen, Anna-Bella Failloux, et al.. West Nile Virus: High Transmission Rate in North-Western European Mosquitoes Indicates Its Epidemic Potential and Warrants Increased Surveillance. PLoS Neglected Tropical Diseases, Public Library of Science, 2015, 9 (7), pp.e0003956. ⟨10.1371/journal.pntd.0003956⟩. ⟨pasteur-01680186⟩

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