Dengue fever: the first episode of indigenous transmission of the year has been identified in mainland France, in Auvergne-Rhône-Alpes

A first episode of indigenous dengue transmission this year in mainland France has been identified in the Auvergne-Rhône-Alpes region and nine cases of chikungunya have now been recorded, Public Health France (SPF) announced on Wednesday, stressing a significant risk of epidemic transmission.

"The first episode of dengue fever for this year 2025 has been identified in Auvergne-Rhône-Alpes, with a start date of symptoms on July ¹ for the only case" detected so far, notes the health agency in its weekly report on the reinforced surveillance of diseases transmitted by tiger mosquitoes.

No episodes of indigenous transmission have been identified in Europe outside of France, the SPF specifies. For chikungunya, the nine outbreaks are located in the regions of Provence-Alpes-Côte d'Azur, Corsica, Occitanie, Auvergne-Rhône-Alpes and, for the first time this year, Grand-Est and Nouvelle-Aquitaine.

This year, indigenous cases of chikungunya are the earliest ever identified in mainland France during the mosquito's active season, and their number is the highest recorded to date. One factor is the epidemic in Réunion and the Indian Ocean.

"Despite a drop in the number of imported cases of chikungunya, particularly from Réunion and the Indian Ocean, their level contributes to the appearance of indigenous transmissions in mainland France," recalls Public Health France.

The risk of epidemic transmission of these viruses in mainland France is also increased by high temperatures: high temperatures contribute to the circulation of the tiger mosquito, a phenomenon accentuated by global warming.

Having appeared in France in 2004, the tiger mosquito continues its rapid expansion there: by the start of 2025, it was present in 81 departments, or 84% of metropolitan departments.

"From 2010, the year of the first indigenous cases of dengue and chikungunya in France, to 2024, 53 episodes of transmission of the dengue, chikungunya and Zika viruses were identified: 48 of dengue, 4 of chikungunya and 1 of Zika" and totaled 277 cases, reports the health agency.

Imported cases are also increasing. Public Health France has counted 1,680 cases of chikungunya, 1,651 of dengue, and 6 of Zika since the beginning of 2025, after 4,683 of dengue, 34 of chikungunya, 8 of Zika, and one dengue-chikungunya coinfection in 2024.