A time-to-event analysis in The Lancet Regional Health, Europe finds the median delay from Aedes albopictus establishment to first locally transmitted dengue or chikungunya outbreak has fallen from 25 years to under five. The interval between successive outbreaks has fallen from 12 years to under one. The study covers European invasions from 1990 to 2024. European surveillance design assumed much longer intervals, and several national programmes have already adjusted.
Published 2026-05-13 · Mosticare Editorial
When the Asian tiger mosquito (Aedes albopictus) was first reported in Belgium in 2000, European health authorities had no immediate cause for alarm. History suggested the lag before any locally transmitted disease would be long. In Italy, where the mosquito was first found in 1990 and established through the 1990s, the first autochthonous chikungunya outbreak did not arrive until 2007, more than a decade later. That gap, roughly 25 years on average across early European invasions, was reassuring. It seemed to suggest that newly colonised countries had time to prepare.
Recent European invasions have followed a much shorter pattern.
A time-to-event analysis published in The Lancet Regional Health, Europe covers European tiger mosquito invasions from 1990 to 2024. It tracked how long a newly established Aedes albopictus population takes to produce its first locally transmitted dengue or chikungunya outbreak. The finding: the median delay has fallen from 25 years in early invasions to under 5 years in recent ones. The interval between successive outbreaks in countries already affected has fallen from roughly 12 years to under one.
Four Numbers That Describe European Vector Risk
The analysis yields two pairs of figures.
The first pair describes the time to initial outbreak: 25 years, then less than 5. The second pair describes recurrence: approximately 12 years between outbreaks, now less than 1.
These are medians across diverse national contexts. They do not mean every new invasion will produce an outbreak within five years. They mean that European surveillance for two decades assumed a long incubation period between arrival and impact. The data show that assumption is now false.
The mechanism behind the acceleration is not mysterious. Aedes albopictus populations are larger, denser, and more widely distributed than in previous decades. The climate envelope that allows viral replication within the mosquito, the extrinsic incubation period, now opens earlier in spring and closes later in autumn. Travel volumes have recovered fully from the pandemic, maintaining a steady flow of viraemic passengers into cities where competent vectors are present. And in regions where the mosquito has been present for years, local adaptation may have produced populations better suited to temperate conditions.
Each factor compounds the others. Together they shorten the interval between establishment and outbreak.
France's PACA Region in 2025
France's PACA region offers a case study that the Lancet data would have predicted.
Aedes albopictus has been established in southern France for years. PACA, which includes Marseille, Nice, and the Côte d'Azur, is not a recent invasion zone. It is a mature, densely established population. In 2025, mainland France recorded 809 autochthonous chikungunya cases. That is an order-of-magnitude jump from earlier French clusters. ECDC records 2 cases in 2010, 12 in 2014, 17 in 2017 and 1 in 2024.
The virus arrived the way it almost always does in Europe: via travellers returning from endemic regions. The mosquito, present in density across the region, amplified it. The 12-year recurrence interval that once separated successive outbreaks did not apply. PACA recorded its next outbreak within a single year.
This is the Lancet paper's "under one year between outbreaks" in practice: a season of 809 cases, following the previous outbreak within a single year.
The Surveillance Assumption the Data Challenge
European vector surveillance was largely designed around the assumption of long lead times. These measures are reasonable when there are years between mosquito establishment and outbreak risk. They include activating response plans when a cluster is confirmed, deploying larval source management in affected communes, and alerting clinicians during peak season.
With a five-year median establishment-to-outbreak interval, that approach requires revision. Surveillance must be continuous and proactive from the moment the mosquito arrives, not reactive once cases appear. Clinicians in regions where Aedes albopictus has recently been confirmed need to consider chikungunya and dengue for fever and joint pain. They should not limit that assessment to August, or to patients who have recently returned from the tropics.
France has already adjusted its programme. ARS Île-de-France activated enhanced tiger mosquito surveillance on 1 May 2026. It runs through 30 November across all eight Île-de-France départements, with 435 egg traps including at three Paris airports. That is a near-year-round posture, consistent with a transmission window that can start in spring and produce an outbreak within a single season.
Where Europe Stands Now
Aedes albopictus is present in 83 of 96 French metropolitan départements as of 1 January 2026. Italy's ISS reports the mosquito in virtually every region. By 30 April 2026 it had recorded 133 imported dengue cases and 13 imported chikungunya cases, all travel-associated.
Germany is at an earlier stage. The mosquito is established in specific districts of Wiesbaden: Südost, Kostheim, and parts of Kastel. Germany's RKI says it has not yet observed any local transmission of dengue, chikungunya or Zika by mosquitoes in Germany, though it notes that conditions for autochthonous transmission exist locally in summer where the tiger mosquito is present. The Mückenatlas citizen-science portal continues to anchor national surveillance.
That present-tense framing is accurate for the present. It is also, in the light of the Lancet analysis, a statement about the present rather than the near future. The mosquito's establishment in Wiesbaden is recent, and the five-year median interval may already apply.
Slovakia provides the most recent datapoint. A 2026 study published in Parasitology Research confirmed Aedes koreicus in Slovakia by molecular evidence. The related invasive species from East Asia has 15 additional European countries identified by climate modelling as suitable for permanent establishment. Aedes koreicus has demonstrated experimental vector competence for chikungunya. It is less widespread than albopictus. Its establishment trajectory in Central and Eastern Europe follows the same logic: arrival, then a compressing lag to first outbreak risk.
The Forward View
The Lancet Regional Health Europe finding pairs with a separate result from the same body of European climate-health research. The Lancet Countdown on Health and Climate Change estimated that the average risk of dengue outbreaks across Europe increased by 297% between 2015 and 2024, against the 1981-2010 baseline, driven by changing Aedes albopictus suitability. The Regional Health Europe analysis provides the mechanistic explanation for why that risk is rising. More places are now climatically suitable for the mosquito, and newly colonised places are reaching outbreak conditions faster than they used to.
In southern Europe, the surveillance calendar now runs through the year.
For countries where Aedes albopictus established recently, the Lancet data indicate an elevated probability of a first autochthonous outbreak before 2030. These include Slovakia, Hungary, Slovenia and parts of Austria. That is a near-term planning horizon.
The establishment-to-outbreak interval is now short enough to be a planning assumption rather than a distant possibility.
What we know
Sources Cited
- The Lancet Regional Health, Europe. Impact of climate and Aedes albopictus establishment on dengue and chikungunya outbreaks in Europe (late 2025; widely cited April, May 2026): https://doi.org/10.1016/S2542-5196(25)00059-2 (paywalled)
- ARS Île-de-France. Tiger-mosquito surveillance activated 1 May 2026: https://www.iledefrance.ars.sante.fr/lutte-antivectorielle-lars-ile-de-france-lance-sa-campagne-de-surveillance-renforcee-partir-du-1er
- Istituto Superiore di Sanità. Dengue and chikungunya surveillance update, 30 April 2026: https://www.epicentro.iss.it/febbre-dengue/aggiornamenti
- Wiesbadenaktuell. Tiger mosquito seasonal update, March 2026: https://wiesbadenaktuell.de/2026/03/26/tigermuecken-saisonbeginn-jetzt-brutstaetten-pruefen-und-vorbeugen/
- Parasitology Research. Aedes koreicus confirmed in Slovakia; 15 further EU countries climatically suitable (2026 online first): https://link.springer.com/article/10.1007/s00436-026-08628-y
- Santé publique France. Chikungunya, dengue et Zika en France hexagonale, bilan 2025: https://www.santepubliquefrance.fr/maladies-a-transmission-vectorielle/chikungunya/bulletin-national/chikungunya-dengue-et-zika-en-france-hexagonale-bilan-2025
- Santé publique France. Face aux moustiques et aux maladies qu'ils transmettent, protégeons-nous, national press release, 6 May 2026: https://www.santepubliquefrance.fr/presse/face-aux-moustiques-et-aux-maladies-quils-transmettent-protegeons-nous
- Robert Koch Institute. FAQ zu durch Stechmücken übertragenen Krankheiten: https://www.rki.de/SharedDocs/FAQs/DE/Muecken/FAQ-Liste.html
- Lancet Countdown on Health and Climate Change Europe. 2026 Report: https://lancetcountdown.org/europe/2026-report/