Secretory NS1’ protein of orthoflavivirus promotes viral transmission to mosquitoes by suppressing the RNAi pathway

Orthoflaviviruses are recognized as significant emerging mosquito-borne pathogens globally. Members of the Japanese encephalitis (JE) serogroup can be distinguished from other orthoflaviviruses by the presence of an additional non-structural protein (NS1’). However, the role of the NS1’ protein in the virus’s life cycle and transmission remains incompletely understood. This study demonstrates that the acquisition of the secretory NS1’ protein from JE serogroup viruses by mosquitoes from infected hosts significantly suppresses the antiviral effect of the RNA interference pathway, thereby facilitating viral infection in mosquitoes. Furthermore, immunization of mice with the NS1’ protein showed considerable efficacy in preventing the transmission of orthoflaviviruses from mice to mosquitoes. These findings indicate that targeting the NS1’ protein may represent a promising strategy for controlling the spread of JE serogroup viruses and other orthoflaviviruses between vertebrate hosts and mosquitoes.