Vector competence of European Aedes mosquito species for Japanese encephalitis virus under fluctuating temperature conditions

The Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus endemic to much of Asia and the Western Pacific, both temperate and tropical regions. Globalisation and the expansion of invasive mosquito species raise concerns about their potential establishment in Europe and other currently non-endemic regions. However, limited knowledge exists regarding the vector competence of European mosquitoes, particularly under the region's characteristic fluctuating temperatures. While <i>Culex</i> species are primary JEV vectors, the role of <i>Aedes</i> mosquitoes remains unclear. This study assessed the vector competence of field-caught or low-generation colony-derived <i>Aedes albopictus</i>, <i>Ae. japonicus</i>, and <i>Ae. vexans</i> from Switzerland under a fluctuating temperature regime (16-28 °C), using <i>Culex quinquefasciatus</i> as a reference. Mosquitoes were exposed to JEV genotype I-b and incubated for 7 and 14 days. RT-qPCR was used to analyse mosquito body parts and saliva to determine infection, dissemination, transmission rates and transmission efficiency. <i>Aedes albopictus</i>, <i>Ae. japonicus</i>, and <i>Cx. quinquefasciatus</i> were competent vectors. <i>Aedes japonicus</i> showed the highest infection rate (13.6%, 9/66) compared to <i>Ae. albopictus</i> (3.0%, 3/101) and <i>Cx. quinquefasciatus</i> (6.9%, 7/101), while <i>Ae. vexans</i> was refractory (0/80). Dissemination was observed in <i>Ae. japonicus</i> already 7 days post-exposure, preceding other species. <i>Aedes japonicus</i> had the highest transmission rate (66.7%, 2/3) and efficiency (6.1%, 2/33). This study demonstrates that European <i>Aedes</i> mosquitoes can serve as JEV vectors under fluctuating temperatures and may contribute to virus transmission despite being considered secondary vectors. The findings emphasise that species-specific assessments under realistic temperatures are essential in evaluating the risk of JEV establishment in temperate regions.