A study published in the Journal of the Royal Society Interface has revised the minimum temperature at which chikungunya can spread from the long-cited 16-18°C down to 13.8°C. For risk planners across Northern and Central Europe, that is not a refinement. It is a season extension of several months and a geography expansion of hundreds of kilometres.
Published 2026-05-13 · Mosticare Editorial
The received wisdom went something like this: chikungunya is a tropical disease. The mosquito that carries it, Aedes albopictus, needs sustained warmth to transmit the virus. Europe has cool nights, rainy springs, and autumns that begin early. That temperature floor, conventionally cited as 16 to 18°C, gave health planners in Northern Europe a comfortable margin of safety.
A paper published in the Journal of the Royal Society Interface in early 2026 has revised that floor downward by 3 to 5 degrees. The new threshold: 13 to 14°C. For risk maps across the continent, that is not a small adjustment. It is the difference between a narrow summer window and a season that begins in April and ends in October.
The Study and What It Found
Researchers at the UK Centre for Ecology & Hydrology (UKCEH), led by epidemiological modeller Sandeep Tegar and senior author Dr Steven White, set out to build more accurate temperature-dependent transmission models for chikungunya in Aedes albopictus. The published result (Journal of the Royal Society Interface, vol 23, DOI: 10.1098/rsif.2025.0707) specifies a full transmission-competence window of 13.8°C to 31.8°C, peaking at 25.6°C.
That lower bound of 13.8°C is the number that matters. It is a realistic midsummer temperature across much of Northern and Central Europe. Southeastern England reaches it for much of July and August. Northern France, Belgium, the Netherlands, and Germany regularly see temperatures in this range from late spring through early autumn. The old 16-18°C figure was not careless guesswork, it was derived from earlier biological data on viral replication rates within the mosquito. The UKCEH team updated those biological inputs and found the transmission-competence range had been underestimated at the lower end.
"The lower temperature threshold that we have identified will therefore result in more areas, and more months of the year, becoming potentially suitable for transmission," Tegar said.
That sentence is worth reading with care. Not more areas in some distant warming scenario. More areas now, under present conditions, when the revised model is applied to current European temperature data.
How Exposed Is Europe, Country by Country?
The UKCEH study mapped transmission risk duration across Europe after applying the corrected threshold. The picture varies starkly by latitude.
Southern Spain and Portugal: 4 to 6 months of potential transmission per year. Malta: March through November, virtually the entire outdoor season. Much of the continent: typically 2 to 3 months, which represents a meaningful widening of the window that existing surveillance calendars account for.
For the United Kingdom, risk remains low. Transmission would only be possible in East Anglia and the south-eastern corner of England during July and August, with scattered pockets elsewhere in the south for about a month, and that assumes the tiger mosquito has established locally, which it has not yet done. Dr White was explicit about why that last caveat matters: "Existing maps do not highlight these UK risk zones. It is important that there is continued action to try to prevent the tiger mosquito from establishing in this country because this highly invasive species is capable of transmitting several infections."
He is not saying transmission is happening in Britain. He is saying the maps do not yet show the zones where it could happen if the mosquito arrives. And the mosquito's European range is expanding year on year.
In France, Aedes albopictus is now established in 83 of 96 metropolitan départements. Italy, where autochthonous chikungunya clusters appeared in recent summers, has the tiger mosquito in virtually every region. The gap between "the mosquito is here" and "the temperature allows transmission" has become, in much of Southern and Central Europe, effectively zero.
Why This Revision Matters Right Now
The 2025 chikungunya season in the Indian Ocean gave Europe a preview of scale. Réunion recorded more than 54,000 confirmed cases. The ECDC counted 32,758 cases and nine deaths across 18 countries by the end of February 2026. Mauritius is the active hotspot as of May 2026, with case counts rising month on month since January.
In the United Kingdom, UKHSA recorded 73 travel-associated chikungunya cases between January and June 2025, up from 27 in the same period of 2024. Most were linked to travel in Sri Lanka, India and Mauritius. The numbers are not alarming in absolute terms. But each returning case is a potential index patient for local transmission, provided a biting mosquito is present.
In France's PACA region, where Aedes albopictus bites humans in nearly every commune, that chain proved more than theoretical. Mainland France recorded 809 autochthonous chikungunya cases in 2025, nearly 60 per cent of them in the PACA region, an unprecedented count for the region. The chikungunya virus arrived from travellers. The tiger mosquito, present in density, did the rest. The UKCEH model would now predict that PACA has the temperature profile to support that kind of outbreak from late spring through mid-autumn.
What the Model Does Not Yet Capture
One important caveat in Tegar's work: the analysis describes vectorial capacity at given temperatures. It does not predict where the tiger mosquito will spread next, or model the interaction of temperature variability, urban heat islands, and land-use change. What it provides is a lower boundary, a threshold below which transmission should not, in principle, occur.
That threshold is now 13°C. Any risk model calibrated to the old 16°C floor will understate the problem. Any surveillance programme designed around a June-to-September window will miss the shoulder seasons that the revised number implies are now relevant.
What to Watch Next
The 2026 European transmission season opens properly in June. This will be the first full season of data under conditions shaped by both the expanded tiger mosquito range and the corrected temperature parameters.
France's ARS Île-de-France activated enhanced tiger mosquito surveillance on 1 May 2026, running through 30 November across all eight départements, including egg traps at three Paris airports. That is the posture of an authority that no longer expects a narrow summer window. Whether other European health agencies follow that lead, or keep running their programmes on the old thermal calendar, is the question this year's season will begin to answer.
What we know
Sources Cited
- Tegar S, Brass DP, Purse BV, Cobbold CA, White SM. "Temperature-sensitive incubation, transmissibility and risk of Aedes albopictus-borne chikungunya virus in Europe." Journal of the Royal Society Interface, vol 23, 2026. DOI: 10.1098/rsif.2025.0707. https://eprints.gla.ac.uk/373335/
- UK Health Security Agency. "Rise in chikungunya cases in UK travellers returning from abroad." GOV.UK, 14 August 2025: https://www.gov.uk/government/news/rise-in-chikungunya-cases-in-uk-travellers-returning-from-abroad
- ARS Île-de-France. "Lutte antivectorielle: l'ARS Île-de-France lance sa campagne de surveillance renforcée." 1 May 2026: https://www.iledefrance.ars.sante.fr/lutte-antivectorielle-lars-ile-de-france-lance-sa-campagne-de-surveillance-renforcee-partir-du-1er
- ECDC. Chikungunya virus disease worldwide overview, situation update March 2026 (web archive, 6 June 2026): https://web.archive.org/web/20260606085119/https://www.ecdc.europa.eu/en/chikungunya-monthly
- UK Centre for Ecology & Hydrology. "Debilitating virus can spread in cool weather, increasing health risk in Europe." 18 February 2026: https://www.ceh.ac.uk/press/debilitating-virus-can-spread-cool-weather-increasing-health-risk-europe
- Santé publique France. "Chikungunya, dengue et Zika en France hexagonale. Bilan 2025." 6 May 2026: https://www.santepubliquefrance.fr/maladies-a-transmission-vectorielle/chikungunya/bulletin-national/chikungunya-dengue-et-zika-en-france-hexagonale-bilan-2025
- Santé publique France / ARS Provence-Alpes-Côte d'Azur. "In 2026: Stepped-up efforts to combat the tiger mosquito!" 7 May 2026: https://www.santepubliquefrance.fr/en/press/2026-stepped-efforts-combat-tiger-mosquito-activation-surveillance-and-control-system
- Santé publique France. "Face aux moustiques et aux maladies qu'ils transmettent, protégeons-nous!" 6 May 2026: https://www.santepubliquefrance.fr/presse/face-aux-moustiques-et-aux-maladies-quils-transmettent-protegeons-nous
- ARS La Réunion. "Chikungunya à La Réunion: point au 5 décembre." 5 December 2025: https://www.lareunion.ars.sante.fr/chikungunya-la-reunion-point-de-situation