Vector Competence of Northern European Culex pipiens Biotype pipiens and Culex torrentium to West Nile Virus and Sindbis Virus

The West Nile Virus (WNV) and Sindbis virus (SINV) are avian-hosted mosquito-borne zoonotic viruses that co-circulate in some geographical areas and share vector species such as Culex pipiens and Culex torrentium. These are widespread in Europe, including northern parts and Finland, where SINV is endemic, but WNV is currently not. As WNV is spreading northwards in Europe, we wanted to assess the experimental vector competence of Finnish Culex pipiens and Culex torrentium mosquitoes to WNV and SINV in different temperature profiles. Both mosquito species were found susceptible to both viruses and got infected via infectious blood meal at a mean temperature of 18 degrees C. WNV-positive saliva was detected at a mean temperature of 24 degrees C, whereas SINV-positive saliva was detected already at a mean temperature of 18 degrees C. Cx. torrentium was found to be a more efficient vector for WNV and SINV over Cx. pipiens. Overall, the results were in line with the previous studies performed with more southern vector populations. The current climate does not seem optimal for WNV circulation in Finland, but temporary summertime transmission could occur in the future if all other essential factors are in place. More field data would be needed for monitoring and understanding the northward spreading of WNV in Europe.

Automated summary

The West Nile and Sindbis viruses are mosquito-borne zoonotic viruses that are widespread in Europe. Finnish Culex pipiens and Culex torrentium mosquitoes were found to be susceptible to both viruses and could transmit them at temperatures ranging from 18 to 24 degrees Celsius. Cx. torrentium was a more efficient vector than Cx. pipiens for both viruses. The current climate in Finland may not be optimal for WNV circulation, but if all other factors are in place, summertime transmission could occur in the future. More field data is needed to monitor the northward spreading of WNV in Europe.