Low risk of transmission of prototype and newly emerged Oropouche virus strains by European Culex pipiens, Aedes albopictus, and Anopheles atroparvus mosquitoes

Abstract
Oropouche virus (OROV) is an emerging arbovirus of growing public health concern, with increasing incidence and geographic spread. Since its discovery in 1955, OROV has caused multiple outbreaks in South and Central America, with a new introduction in Cuba since May 2024. Recent travel-related cases in Europe and the Americas underscore its potential for global dissemination. Assessing vector competence outside endemic regions is critical in the context of global travel and climate change. We evaluated the vector competence of three mosquito species commonly found in Europe—Culex (Cx.) pipiens, Aedes (Ae.) albopictus, and Anopheles (An.) atroparvus—using two OROV strains: the prototype TRVL9760 (1955, Trinidad and Tobago) and a recent isolate OROV-IRCCS-SCDC_1/2024 (2024, imported from Cuba to Italy). Mosquitoes were orally infected and examined at 7- and 14-days post-infection. We assessed infection (body), dissemination (peripheral tissues), and transmission potential (saliva) by measuring infectious virus particles using the gold standard focus-forming assays. Our findings show that Cx. pipiens and An. atroparvus were not susceptible to infection or did not allow transmission with OROV. In Ae. albopictus, low infection rates were observed: 6.7% of mosquitoes showed infection at day 7 with the prototype strain, and 3.1% at day 14 with OROV-IRCCS-SCDC_1/2024. All infected mosquitoes showed viral dissemination, but none had infectious virus in their saliva, indicating low risk for transmission. These results confirm limited vector competence of European mosquito species for OROV and emphasize the importance of continued entomological surveillance to inform future risk assessments.

Author summary
Mosquitoes found in Europe could potentially spread new viruses that are not established here yet, such as Oropouche virus. We studied whether European mosquitoes could carry and transmit two different strains of Oropouche virus: an old and well-known strain and another that has only recently emerged. Two common European mosquito species (Culex pipiens and Anopheles atroparvus) could not carry or spread Oropouche virus, no matter which strain was tested. The invasive Asian tiger mosquito (Aedes albopictus), which is already present in parts of Europe, was able to pick up both strains of the virus but did not pass them on. This study aims to generate data to support risk assessments of a currently circulating OROV strain in non-endemic regions of Europe. It also contributes to preparedness efforts in light of ongoing environmental and epidemiological changes and helps assess potential health risks for travelers to and from affected areas.