Simultaneous Coinfections with West Nile Virus and Usutu Virus in and Mosquitoes.

The mosquito-borne zoonotic flaviviruses West Nile virus (WNV) and Usutu virus (USUV) are endemic in many European countries and emerged in Germany in recent years. Due to the increasing overlap of their distribution areas and their similar epidemiology, coinfections of WNV and USUV are possible. Indeed, coinfections in vertebrate hosts as a rare event have already been reported from some countries including Germany. However, it is largely unknown whether and to what extent coinfections could affect the vector competence of mosquitoes for WNV and USUV. For this purpose, the mosquito species biotype , biotype , and were orally infected in mono- and simultaneous coinfections with German strains of WNV and USUV. Mosquitoes were incubated for 14 days at 26°C, 85% relative humidity, and a 16 : 8 light-dark photocycle, before they were dissected and forced to salivate. The results showed a decrease in USUV susceptibility in biotype , an increase in USUV susceptibility in , and no obvious interaction between both viruses in biotype . Vector competence for WNV appeared to be unaffected by a simultaneous occurrence of USUV in all tested mosquito species. Coinfections with both viruses were only found in mosquitoes, and cotransmission of WNV and USUV was observed in biotype . Overall, our results show that viral interactions between WNV and USUV vary between mosquito species, and that the interaction mainly occurs during infection and replication in the mosquito midgut. The results of this study confirm that to fully understand the interaction between WNV and USUV, studies with various mosquito species are necessary. In addition, we found that even mosquito species with a low susceptibility to both viruses, such as , can play a role in their transmission in areas with cocirculation.