Chikungunya cases have continued to increase in mainland France in recent days, Public Health France observed on Wednesday, in a summer marked by the increase, early onset and geographic expansion of cases of viral diseases transmitted by mosquitoes.
As of August 26, 30 outbreaks of indigenous chikungunya transmission, totaling 228 cases, have been identified in mainland France, the health agency summarized in a weekly report, i.e. "3 new episodes of chikungunya transmission (in Occitanie, Paca and Nouvelle-Aquitaine)."
While several episodes are now over, the summer of 2025 is of unprecedented scale in mainland France for indigenous cases of chikungunya, the virus of which is transmitted from one human to another via tiger mosquito bites.
"The significant number of chikungunya outbreaks observed this year and their early occurrence are linked to the epidemic that has raged in Réunion and the Indian Ocean region, caused by a viral strain well adapted to the Aedes albopictus mosquito," the health agency recalled. The major epidemic in Réunion facilitated the arrival of imported cases, which then favored contamination in mainland France.
Another disease transmitted by the tiger mosquito and on the rise, dengue fever does not currently have as many indigenous cases as in 2024 – with a record of 66 in mainland France – but outbreaks have been regularly identified since July.
However, there has been no further weekly increase and, of the seven outbreaks identified in mainland France at this stage, four are closed.
The cases of chikungunya and dengue fever identified so far are located in the Provence-Alpes-Côte d'Azur, Corsica, Occitanie, Auvergne-Rhône-Alpes regions, already affected in previous years, and for the first time in Grand Est, Nouvelle-Aquitaine and Bourgogne-Franche Comté.
The latest disease under increased surveillance: West Nile fever, which is not transmitted by the tiger mosquito but by the Culex variety, more common in mainland France.
With 15 indigenous cases identified so far, there has certainly been no record broken this summer in mainland France, but their location confirms a growing transmission outside the historical Mediterranean arc. In addition to those in Paca and Occitanie, several cases have been identified in Île-de-France for the first time.
Europe has recorded a record number of cases of mosquito-borne diseases such as chikungunya and West Nile virus this year, a "new normal" created by climate change, the European Union's health agency announced last Wednesday, urging greater prevention than ever.
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