Scientists Find Chikungunya Spreads at 13°C — 3 to 5 Degrees Colder Than Europe Planned For

By David Ogilvy, Chief Marketing Officer at Mosticare Global | Published 2026-05-13

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. Continental Europe from Paris to Warsaw: 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 southeastern England during July and August, 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 accumulated roughly 450,000 cumulative cases. WHO's rapid risk assessment for the SAGE group counted 32,758 cases and 9 deaths across 18 countries by late 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 160 travel-associated chikungunya cases in 2025 — up from 112 in 2024 and 45 in 2023. Most were linked to travel in Sri Lanka, India and Bangladesh. 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. PACA recorded 809 autochthonous chikungunya cases in 2025, an order-of-magnitude jump from any prior year. 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. ECDC's annual arbovirus surveillance report, expected in autumn 2026, will be the first to incorporate a 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

1. Tegar S et al. "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. Summarised by MedicalXpress: https://medicalxpress.com/news/2026-02-debilitating-tropical-virus-cool-weather.html
2. UK Health Security Agency. "Rise in chikungunya cases in UK travellers returning from abroad." GOV.UK, 2026: https://www.gov.uk/government/news/rise-in-chikungunya-cases-in-uk-travellers-returning-from-abroad
3. 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
4. WHO / SAGE. Chikungunya virus rapid risk assessment, data cut-off 28 February 2026: https://cdn.who.int/media/docs/default-source/_sage-2026/who-rapid-risk-assessment_chikungunya-virus_global_v1.pdf