By Zheng Qi 2021-02-17

Dengue, once considered a geographically contained tropical disease, has dramatically expanded its global footprint over recent decades and is now firmly established as a year-round threat across virtually all tropical regions worldwide. Its primary mosquito vector, Aedes aegypti, is perfectly adapted to urban and semi-urban environments in these climates, thriving in densely populated cities where abundant artificial water containers—from discarded plastic bottles and old tires to uncovered water storage jars and flowerpot saucers—provide endless breeding sites. This mosquito’s close cousin, Aedes albopictus (commonly known as the Asian tiger mosquito), has further extended the disease’s potential range due to its remarkable ecological adaptability; it can survive in slightly cooler temperate zones, withstand longer transportation in cargo shipments, and breed in both natural and man-made water collections. Together, these two highly adaptive species have pushed dengue transmission into subtropical and even some temperate regions during warmer months, with established local outbreaks now documented as far north as southern Europe, the southeastern United States, and parts of East Asia previously considered low-risk.

The global distribution of dengue is fundamentally shaped by a combination of climatic, environmental, and human factors. High humidity and consistently warm temperatures—typically above 20°C—are essential for mosquito survival, egg development, and viral replication within the mosquito, which is why transmission peaks during and after rainy seasons in endemic countries. However, contrary to popular belief, dengue outbreaks can occur at any time of year as long as local Aedes mosquito populations remain active, meaning even brief warm spells in otherwise cooler regions can trigger localized transmission if infected mosquitoes or travelers introduce the virus. Urbanization, international travel, and climate change are accelerating this spread: densely packed cities with unreliable water supplies encourage residents to store water in open containers, creating ideal mosquito breeding habitats, while global trade and tourism constantly move infected individuals and mosquito eggs across borders.

International travelers play a significant yet often overlooked role in dengue geography. A person infected abroad can return home during the virus’s incubation period—before showing any symptoms—and if bitten by local Aedes mosquitoes in a non-endemic area, they can spark a chain of local transmission, turning a single imported case into a community outbreak. This “travel-associated dengue” has been responsible for introducing the virus into regions like southern France, Croatia, Florida, and southern China, where seasonal mosquito activity aligns with the return of tourists or business travelers from endemic zones. Once introduced, the virus can circulate locally until colder temperatures reduce mosquito activity, creating a recurring seasonal transmission risk in these areas.

While Southeast Asia and the Americas currently report the highest number of annual dengue cases, nearly half of the world’s population now lives in countries where dengue is endemic, and climate projections suggest that rising global temperatures will expose an additional 2–3 billion people to Aedes mosquito habitats by the end of this century. This expanding geographic reach means that dengue is no longer just a “tropical problem”—it is a growing global health challenge that demands coordinated surveillance, climate-resilient vector control, and increased public awareness in both endemic and emerging at-risk regions.

Edited by: Secretariat of the Asia-Pacific Network for Drug and Diagnostics Innovation
Produced by: Zheng Qi
Reviewed by: Zhang Haobing
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