Dengue and chikungunya interface in South and Southeast Asia: Epidemiology, challenges and future directions.

Dengue and chikungunya are major arboviral diseases imposing an increasing public health burden across South and Southeast Asia. Both viruses are transmitted primarily by Aedes aegypti and Aedes albopictus, vectors that thrive in rapidly urbanizing and climate-sensitive environments. Dengue has become hyperendemic over recent decades, with increasingly severe and frequent outbreaks, while chikungunya has re-emerged since the mid-2000s, driven by viral adaptation and expanded vector competence. Their concurrent circulation presents substantial challenges, including overlapping clinical manifestations, diagnostic uncertainty, documented co-infections, and increased pressure on healthcare systems. Climate change, unplanned urbanization, and population mobility further intensify transmission dynamics and economic costs. This review synthesizes current evidence on epidemiology, geographical distribution, vector ecology, co-circulation, and underlying drivers of dengue and chikungunya in South and Southeast Asia. It highlights key challenges in surveillance, diagnostics, vector control, and health system capacity, and discusses future priorities, including integrated surveillance, vector control strategies, and regional cooperation.