Key Points

• In 2025, during the enhanced surveillance period (May 1 to November 30), the following were identified in mainland France:
  • 809 locally acquired cases of chikungunya, including 790 cases spread across 79 transmission episodes (1 to 144 cases per episode) and 19 isolated cases for which the place of infection could not be determined. The onset dates of symptoms ranged from May 27 to November 13.
  • 30 locally acquired cases of dengue, including 29 distributed across 11 transmission episodes (1 to 10 cases per episode) and 1 isolated case for which the site of infection could not be identified. The onset dates of symptoms ranged from June 25 to September 14. 
• Episodes of local transmission occurred in the Provence-Alpes-Côte d'Azur, Occitanie, Auvergne-Rhône-Alpes, Corsica, and Île-de-France regions, which had already been affected in previous years, and, for the first time, in Nouvelle-Aquitaine, Grand Est, and Bourgogne-Franche-Comté.
• The high number of chikungunya cases reported in 2025, as well as their early onset in the season, can be attributed to the epidemic that occurred in the Indian Ocean, particularly in Réunion. This epidemic was caused by a viral strain particularly well-suited to the Aedes albopictus mosquito.