Experimental infection of Oropouche virus in Japanese populations of Aedes albopictus and Culex mosquitoes.

The recent geographical expansion of Oropouche virus (OROV) highlights the critical need to evaluate vector competence in non-endemic regions. This study aimed to evaluate the susceptibility of major Japanese mosquito populations (Culex quinquefasciatus, Cx. pipiens pallens, and Aedes albopictus) and a South African reference strain of Cx. quinquefasciatus to the OROV prototype strain (TRVL9760) by intrathoracic injection (ITI) and oral exposure (OE) experiments. Following ITI, 100% of the tested mosquitoes developed infections with high viral replication, particularly Ae. albopictus, demonstrating its robust cellular permissiveness. Conversely, OE yielded low infection rates in the thorax and abdomen (0-18.9%) and failed to cause systemic dissemination to secondary tissues (head, wings, and legs). These results demonstrate that the stringent midgut barriers that prevent OROV dissemination are maintained in both Japanese and reference mosquito strains. However, the robust viral replication observed upon bypassing these barriers reveals a significant latent susceptibility. By elucidating these dynamics, this study provides the first scientific evidence of the intrinsic susceptibility of Japanese mosquitoes to OROV. This foundational knowledge is not only critical for assessing current transmission risks but also serves as an essential baseline to determine whether contemporary epidemic lineages might overcome these physiological constraints in the future.