UK mosquitoes are competent to transmit Usutu virus at native temperatures

Usutu virus (USUV) is an emerging zoonotic virus transmitted primarily by <i>Culex</i> mosquitoes. Since its introduction into Europe from Africa during the late 20th century, it has caused mortality within populations of passerine birds and captive owls, and can on occasion lead to disease in humans. USUV was first detected in the UK in 2020 and has become endemic, having been detected in either birds and/or mosquitoes every subsequent year. Importantly, the vector competence of indigenous mosquitoes for the circulating UK (London) USUV strain at representative regional temperatures is still to be elucidated. This study assessed the vector competence of five field-collected mosquito species/biotypes, <i>Culex pipiens</i> biotype <i>molestus</i>, <i>Culex pipiens</i> biotype <i>pipiens</i>, <i>Culex torrentium</i>, <i>Culiseta annulata</i> and <i>Aedes detritus</i> for the London USUV strain, with infection rates (IR) and transmission rates (TR) evaluated between 7 and 28 days post-infection. Infection and transmission were observed in all species/biotypes aside from <i>Ae. detritus</i> and <i>Cx. torrentium</i>. For <i>Cx. pipiens</i> biotype <i>molestus</i>, transmission potential suggests these populations should be monitored further for their role in transmission to humans. Furthermore, both <i>Cx. pipiens</i> biotype <i>pipiens</i> and <i>Cs. annulata</i> were shown to be competent vectors at 19 °C indicating the potential for geographical spread of the virus to other UK regions.