Why dengue is expanding beyond the tropics

For decades, dengue was something travelers brought back from the tropics. Increasingly, it is being transmitted locally in temperate regions — including southern France, Italy, Spain, and Croatia — where the tiger mosquito Aedes albopictus is now established.

What changed

• Vector range. Aedes albopictus has spread across much of southern and central Europe, establishing the conditions for local transmission once the virus is introduced by a viremic traveler.
• Warmer, longer seasons. Higher temperatures shorten the virus's extrinsic incubation period in the mosquito and lengthen the transmission window.
• More introductions. Record global dengue activity — 2024 was the largest year on record — means more viremic travelers seeding local outbreaks.

The numbers

Europe has moved from a handful of autochthonous cases a decade ago to hundreds in recent peak years, clustered in late summer and early autumn. These remain small, localized clusters — not endemic transmission — but the trend line is clear and consistent.

Implications for travelers

• Dengue is now a summer consideration for parts of Europe, not only tropical itineraries.
• Risk is seasonal and focal: late summer, in specific affected areas, after wet weather.
• The practical advice is unchanged but newly relevant closer to home: daytime bite prevention in affected regions during the warm months.

Bottom line: "Dengue is tropical" is now an outdated mental model. Trip-planning should weigh local transmission risk by season, not just by latitude.