Vector competence of northern European Culex pipiens biotypes and hybrids for West Nile virus is differentially affected by temperature

Abstract

BackgroundOutbreaks of West Nile virus (WNV) have not occurred in northern Europe despite nearby circulation of WNV in the southern part of the continent. The main vector for WNV, the mosquito Culex (Cx.) pipiens, consists of two behaviorally distinct biotypes, pipiens and molestus, which can form hybrids. Although temperature has been shown to influence vector competence of Cx. pipiens for WNV and biotypes are differentially susceptible towards infection, the interaction between the two has not been elucidated.MethodsWe determined vector competence of the Cx. pipiens biotypes and hybrids, after 14 days of incubation at 18, 23 and 28 °C. Mosquitoes were orally infected by providing an infectious blood meal or by injecting WNV directly in the thorax. Infection and transmission rates were determined by testing the bodies and saliva for WNV presence. In addition, titers of mosquitoes with WNV-positive bodies and saliva samples were determined.ResultsOrally infected biotype pipiens and hybrids showed significantly increased transmission rates with higher temperatures, up to 32 and 14 %, respectively. In contrast, the molestus biotype had an overall transmission rate of 10 %, which did not increase with temperature. All mosquitoes that were infected via WNV injections had (close to) 100 % infection and transmission rates, suggesting an important role of the mosquito midgut barrier. We found no effect of increasing temperature on viral titers.ConclusionsTemperature differentially affected vector competence of the Cx. pipiens biotypes. This shows the importance of accounting for biotype-by-temperature interactions, which influence the outcomes of vector competence studies. Vector competence studies with Cx. pipiens mosquitoes differentiated to the biotype level are essential for proper WNV risk assessments.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1677-0) contains supplementary material, which is available to authorized users.

The role of Culex pipiens mosquitoes in transmission of West Nile virus in Europe

“…However, other factors such as vector competence and climate determine whether transmission cycles can get established. Such factors are most likely limiting the transmission of WNV in northern Europe (Fros et al 2015a, Vogels et al 2016a. Future studies on vector competence of the Cx.…”

“…In this study, the same protocols were used as described before (Vogels et al 2016a). In order to test for the effect of population and temperature on WNV infection and transmission rates, mosquitoes were orally exposed to WNV.…”

“…The F4-6 offspring of both populations were used in experiments. Mosquitoes were reared as described before (Vogels et al 2016a). In short, larvae and adults from both colonies were maintained at 23 °C with a 16:8 L:D cycle and 60 % relative humidity.…”

“…Culex pipiens mosquitoes originating from The Netherlands and Germany have been found to be competent vectors for WNV (Fros et al 2015a, Leggewie et al 2016, Vogels et al 2016a). However, studies in both Europe and North America have not only shown spatial and temporal variation in vector competence among different mosquito populations (Kilpatrick et al 2010, Leggewie et al 2016, Vaidyanathan & Scott 2007, but also variation in vector competence due to environmental factors (Fros et al 2015a, Kilpatrick et al 2008, Vogels et al 2016a).…”

“…However, studies in both Europe and North America have not only shown spatial and temporal variation in vector competence among different mosquito populations (Kilpatrick et al 2010, Leggewie et al 2016, Vaidyanathan & Scott 2007, but also variation in vector competence due to environmental factors (Fros et al 2015a, Kilpatrick et al 2008, Vogels et al 2016a). This suggests that both genetic and environmental factors play an important role in vector competence, which may explain the differences in WNV transmission across Europe.…”