Dengue is settling into Europe, and models put much of France in range by 2085

Locally acquired dengue is no longer only a tropical souvenir carried home by travellers in Europe: in 2024, Italy recorded 296 autochthonous cases across four regions, the largest number of locally transmitted cases ever documented on the European mainland [s2]. A mechanistic model published this month projects that by 2085, under a high-emissions scenario, 89% to 96% of France would be climatically suitable for Aedes albopictus, the tiger mosquito that spreads the virus, with local transmission theoretically possible across 71% to 95% of the country [s1]. The direction of travel is what surveillance teams have been warning about, quantified.

What Italy's 2024 outbreak showed

The Italian analysis is the closest thing Europe has to a controlled look at how autochthonous dengue actually spreads on the continent. Researchers examined 296 locally acquired cases of dengue virus serotype 2 with symptom onset between 31 July and 31 October 2024, reconstructing transmission chains in three major foci with a Bayesian framework [s2]. Peak reproduction numbers ranged from 1.35 to 3.33, and the mean generation time — the interval between one person's infection and the next in the chain — was 18.0 days (95% credible interval 15.5–20.0) [s2].

Two findings matter for control. Transmission was overwhelmingly local: among cases with an identified source, fewer than 1% of infections occurred beyond 400 metres, and household transmission accounted for 15.4% of events (95% CrI 12.6–17.4%) [s2]. And it responded to intervention: after outbreaks were detected, the average number of secondary cases per infection fell from 1.4 to 0.4, and vector-control measures were associated with a 41.0% reduction in transmission (95% CI 6.6–63.3%) [s2]. The catch is speed — a short-range, fast-cycling outbreak rewards early detection and punishes a slow one.

Temperature is doing measurable work

The same study put a number on the climate link that usually stays qualitative. Each 1°C rise in temperature was associated with a 19.8% increase in transmission (95% CI 11.3–29.0%) [s2]. That is not a projection or a model output; it is an association measured inside a real European outbreak, which is why it carries weight the long-range forecasts cannot.

The long-range forecasts then extend it. The French modelling study, calibrated against records of recent autochthonous cases in France, simulated mosquito establishment and dengue transmission risk to 2085 under three regional climate models [s1]. Under the high-pressure scenario — high greenhouse-gas emissions and high population growth — most of France (89%–96%) becomes climatically suitable for Ae. albopictus, sparing mainly the mountain ranges, and autochthonous transmission becomes possible across 71% to 95% of the territory, excluding the northern lowlands [s1]. Under a median scenario of moderate emissions and demographic stagnation, the picture is far more uncertain: suitability for establishment spans 49% to 89%, and transmission risk 31% to 82%, depending on the climate model [s1]. The wide spread is itself the message — the outcome is not fixed, and the emissions path moves it substantially.

Why this counts as range expansion, not a one-off

A single hot summer producing local cases could be noise. What the record now shows is repetition. Dengue has historically been viewed in Europe primarily as a travel-associated infection, but recurrent autochthonous outbreaks in Italy, Spain and France indicate an evolving epidemiology of repeated seasonal transmission in areas where competent Aedes vectors are already established [s3]. Globally, dengue is the most rapidly expanding arboviral infection, and Europe now sits at the leading edge of that expansion rather than outside it [s3]. The convergence of established vectors, imported viraemic cases and warming seasons is the mechanism, and none of those three ingredients is retreating.

What it does not establish

The French projections are scenario-dependent and reach to 2085; they describe climatic suitability, not a forecast of case counts, which also depend on mosquito abundance, imported infections, housing, surveillance and control that models handle only crudely [s1]. The 19.8%-per-degree figure comes from one outbreak season in one country and should not be treated as a universal constant [s2]. And these are studies of transmission risk and spread, not of clinical severity — most autochthonous European dengue to date has been comparatively mild, though serotype and prior exposure can change that.

What to watch

Whether 2024's Italian record holds or is beaten; whether autochthonous transmission appears in countries and latitudes that have not seen it; and whether Europe's surveillance and vector-control systems can consistently hit the early-detection window the Italian outbreak showed is decisive. The biology is now permissive across much of the continent for part of the year. What determines the public-health outcome is how fast the response moves once the first local case is confirmed.

Sources

1. [s1] Aedes albopictus and Dengue Transmission Risk in France Over the 21st Century. Global Change Biology, August 10, 2026. https://doi.org/10.1111/gcb.71017
2. [s2] Autochthonous transmission patterns of dengue virus serotype 2 in Italy: evidence from outbreaks in 2024. Eurosurveillance, July 10, 2026. https://doi.org/10.2807/1560-7917.es.2026.31.27.2600035
3. [s3] Preparing Europe for Recurrent Autochthonous Dengue Transmission: Public Health Implications and Preparedness Priorities. The Lancet Regional Health – Europe, June 24, 2026. https://doi.org/10.1016/j.lanepe.2026.101758