France reports more locally acquired dengue and chikungunya cases this season, with outbreaks in several regions. Here is what the latest surveillance data shows.
The disease risk has moved closer to home
Each year, from May to November, public health agencies in France run enhanced surveillance for chikungunya, dengue and Zika. The reason is simple. The mosquito that carries these viruses, Aedes albopictus, is now established in large parts of the country. When a traveller returns with one of these viruses, a local mosquito can bite that person and then pass the virus to someone else. This is how locally acquired cases begin. In 2024, such cases were very rare. By 2025, the picture had changed. The latest data for 2026 show continued activity, with more episodes than in the previous weeks. Understanding these numbers matters for anyone planning travel or living in affected areas. The figures come directly from the national surveillance bulletins and from European monitoring reports.
Eleven local episodes, and most are chikungunya
As of 24 August 2026, Santé publique France had identified 11 episodes of autochthonous vector-borne transmission in mainland France. That is five more than the week before. Seven of these episodes were chikungunya, adding up to 33 cases. Each episode involved between 1 and 19 people. The affected areas included the Tarn and Lot in Occitanie, Gironde in Nouvelle-Aquitaine, and Val-de-Marne in Ile-de-France. The remaining four episodes were dengue, with five cases in total. These occurred in the Tarn and Hérault in Occitanie, Dordogne in Nouvelle-Aquitaine, and Bouches-du-Rhône in Provence-Alpes-Côte d'Azur. For every episode, the agency said that investigations were under way and that prevention and control measures had been launched. This pattern shows that local spread is no longer confined to the south. It has reached regions farther north.
Europe is watching these figures closely
The European Centre for Disease Prevention and Control, known as ECDC, also tracks this situation. In its report for week 35 of 2026, which covers the end of August, ECDC confirmed that France was the only country in Europe to report locally acquired chikungunya cases this year. It counted 33 cases and noted eight additional cases since the previous update, as well as four new clusters. For dengue, France reported five locally acquired cases. Four clusters were recorded, two of them still active. One new cluster had appeared since the last report. ECDC said it would keep publishing weekly updates until November 2026. The purpose is to give public health authorities the information they need to respond. This European perspective confirms that the situation in France is exceptional for the region and deserves close attention.
Why this season is different from earlier years
To see why this season stands out, look back at the recent past. Between 2004 and 2024, locally transmitted chikungunya in mainland France was almost unknown, with only three recorded episodes. Those were two cases in Fréjus in 2010, 12 in Montpellier in 2014 and 17 in Le Cannet-des-Maures in 2017. Then, in 2025, the numbers rose sharply. That year, 809 locally acquired chikungunya cases were identified in mainland France. The Santé publique France data page calls this the highest number since enhanced surveillance began in 2006. The rise was linked to a large outbreak on Réunion Island, which produced many imported cases. The 2025 season also started earlier than usual, and some local outbreaks appeared in May. The current 2026 figures continue this trend but with fewer cases than the previous year.
Imported cases are a key part of the story
No local transmission can begin without a source of the virus. In France, that source is usually a traveller returning from a region where dengue or chikungunya is already circulating. The surveillance data show how important these imports are. Between 1 May and 23 August 2026, Santé publique France counted 117 imported chikungunya cases, 328 imported dengue cases and 11 imported Zika cases in mainland France. In 2025, a similar pattern appeared. By 10 July of that year, 1,911 imported chikungunya cases had been notified, and 89 percent of them were linked to travel to Réunion Island. These imported cases can seed new local outbreaks when the right mosquito is present. This is why health agencies ask travellers to protect themselves from bites and to report any symptoms after returning home.
West Nile virus is also appearing
Dengue and chikungunya are not the only mosquito-borne viruses to watch this year. The national bulletin also recorded 30 autochthonous West Nile virus infections as of 24 August 2026. That is 12 more than the previous week. These cases were spread across Provence-Alpes-Côte d'Azur, Occitanie, Ile-de-France and Auvergne-Rhône-Alpes. For the first time, human West Nile cases were detected in the Aude, Seine-et-Marne and Drôme departments. West Nile virus is normally carried by different mosquitoes, often Culex species, and has a different cycle involving birds. Most people who become infected have no symptoms, but a small number can develop a serious neurological illness. The appearance of this virus in new areas shows that the range of mosquito-borne diseases is expanding. It also highlights the value of comprehensive surveillance across France.
The outlook for the rest of the season
What can we expect in the coming weeks? The enhanced surveillance period lasts until the end of November, when cooler weather reduces mosquito activity. In the past, outbreaks have continued into the autumn, so public health agencies will not stop monitoring yet. They are already running investigations for each new episode and applying control measures to limit further spread. These measures may include insecticide treatment, removing standing water and informing local communities. For residents and visitors, the most effective steps are simple: use repellent, cover skin at dawn and dusk, and empty any containers that collect water. No vaccine for chikungunya is widely available in Europe, and dengue vaccines have limitations. So prevention still depends on avoiding mosquito bites. By keeping an eye on the weekly bulletins, you can stay informed about where the risk is highest.
Sources
- Chikungunya, dengue, Zika et West Nile en France hexagonale. Bulletin de la surveillance renforcée du 26 août 2026.: Santé publique France
- Weekly Communicable Disease Threats Report, Week 35, 22 - 28 August 2026: European Centre for Disease Prevention and Control
- Data for mainland France: Santé publique France
- Multiple early local transmissions of chikungunya virus, Mainland France, from May 2025: Eurosurveillance