Species-specific susceptibility and low transmission of the historical Japanese encephalitis virus Nakayama strain in North American Culex mosquitoes

Japanese encephalitis virus (JEV) is an emerging mosquito-borne flavivirus with potential for geographic expansion, yet the risk of establishment in North America remains poorly characterized. We assessed vector competence of three North American Culex species ( Cx. pipiens, Cx. quinquefasciatus, and Cx. tarsalis ) for the JEV Nakayama strain, isolated from human brain in 1934 in Japan, across five constant temperatures (15, 20, 25, 30, and 33°C) at 4, 7, and 14 days post-feeding, quantifying infection, dissemination, and transmission rates. Vector competence was low but non-zero across all species. Cx. pipiens showed higher infection rates than the other species, whereas Cx. quinquefasciatus and Cx. tarsalis were minimally susceptible under these experimental conditions. Temperature had limited effects on infection and no detectable effects on dissemination or transmission. These findings suggest limited transmission potential of JEV Nakayama in North America, with Cx. pipiens as a relatively permissive vector.