Global source-sink dynamics of dengue viruses and epidemic establishment in areas on the fringe of endemic transmission.

The global expansion of dengue virus (DENV) poses a major public health threat, yet its circulation dynamics remain poorly understood. By integrating global genetic, epidemiological, and mobility data within a phylodynamic framework, we show that DENV circulation follows a source-sink model, with tropical endemic regions acting as persistent viral reservoirs ('sources') that seed epidemics in temperate areas ('sinks'). Most areas at the fringe of endemic transmission exhibit sink-like characteristics with exception of South China. We identify a low-intensity dispersal route from South China to endemic Asia compared with the high-intensity source-to-sink direction, along with occasional DENV1 overwintering events in South China. Together, these findings suggest that South China occupies an intermediate state between endemic and non-endemic areas. These global DENV pathways were primarily driven by air travel and were reshaped by COVID-19 pandemic-related perturbations. Our findings highlight that dengue circulates within a fully interconnected global system that requires a shift from localized control to globally coordinated intervention efforts, as well as emphasize the importance of year-round genomic surveillance at the human-vector interface in fringe areas.