First whole-genome detection of dengue virus in urban Aedes aegypti from Southern Brazil.

Dengue virus (DENV) is a major global health threat whose expansion into temperate regions has been facilitated by climate change and vector adaptation. Despite recurrent epidemics in Brazil, genomic surveillance in mosquito vectors remains limited, particularly in southern regions, constraining our understanding of local transmission dynamics and viral evolution. Here, we aimed to investigate dengue virus circulation, serotype co-circulation, and genomic signals of viral adaptation through vector-based genomic surveillance in southern Brazil. Using this approach, we provide genomic evidence of dengue virus circulation in southern Brazil during 2023. Whole-genome sequencing revealed active circulation of both DENV-1 (Genotype V) and DENV-2 (Genotype II), with the detection of mosquito pools harboring both serotypes, indicating their simultaneous circulation and raising concerns about increased transmission complexity and sequential infection risk in humans. Phylogenetic analyses supported sustained local transmission alongside multiple viral introductions. Moreover, recurrent mutations, particularly in non-structural proteins (NS1, NS2A, and NS5), suggest ongoing viral adaptation. These findings represent the first vector-derived genomic data for dengue in southern Brazil and highlight the critical role of mosquito-based genomic surveillance in detecting co-circulating serotypes, monitoring viral evolution, and strengthening preparedness in emerging transmission settings.