First mosquito-based molecular evidence of tembusu virus in Vietnam

BACKGROUND: Mosquito-borne flavivirus diversity in Vietnam remains incompletely characterized. Tembusu virus (TMUV), an emerging flavivirus associated with ducks and other avian hosts, has been reported in poultry in Vietnam, but molecular evidence from field-caught mosquitoes has been lacking. METHODS: We screened 10,658 mosquitoes representing four major arbovirus vector species, including Aedes aegypti, Ae. albopictus, Culex quinquefaciatus, Cx. tritarniorhynchus, collected across multiple ecological settings in Vietnam. Mosquitoes were grouped into 586 pools and tested using broad-range reverse transcription polymerase chain reaction assays targeting flaviviruses and alphaviruses. Positive flavivirus amplicons were subjected to sequencing, and one TMUV-positive pool underwent deeper sequencing and phylogenetic analysis. RESULTS: The Cx. tritaeniorhynchus pool (25 specimens) collected in rural southern Vietnam yielded a TMUV draft genome. In the complete genome phylogeny, the Vietnamese mosquito-derived sequence clustered within a distinct monophyletic clade comprising strains from China, Thailand, Taiwan, and Vietnam. CONCLUSIONS: These findings provide the first mosquito-based molecular evidence of a TMUV-related virus in Vietnam and suggest that mosquito surveillance can reveal previously unrecognized viral diversity and transmission patterns.