The Regional Health Agency (ARS) is therefore calling for heightened vigilance, especially regarding the symptoms and risks associated with mosquito bites.
At least three confirmed cases in Auvergne-Rhône-Alpes
The ARS Auvergne-Rhône-Alpes has been informed in recent days of several reports of human cases of West Nile virus infection, also called West Nile virus. To date, at least three confirmed human cases have been identified in the Rhône, Drôme, and Isère. These first detections in the region demonstrate local circulation of the virus. Several equine cases have also been reported. West Nile virus is mainly present in birds. It is transmitted by Culex mosquitoes, also called common mosquitoes, which become contaminated when they bite infected birds.
A circulation spreading to new territories
The presence of West Nile virus is gradually extending across mainland France. In 2025, 62 cases of locally acquired human infection had been identified in six French regions, notably in Provence-Alpes-Côte d'Azur, Occitanie and Nouvelle-Aquitaine, but also, for the first time, in Île-de-France, Auvergne-Rhône-Alpes and Normandy. Today, there are 120 cases across the country. Worth noting: several cases detected in the same area and during the same period don't necessarily mean that people infected each other. Humans and horses are indeed considered "epidemiological dead ends": they don't allow the virus to be transmitted to a mosquito afterward.
What are the symptoms?
In approximately 80% of cases, the infection causes no symptoms. When it does manifest, it can however resemble flu-like syndrome, notably with fever, achesheadaches, muscle pain, or sometimes a skin rash. More rarely, around 1% of infections can lead to neurological complications such as meningitis or encephalitis. The sudden onset of fever, especially when accompanied by neurological signs or behavioral changes, should prompt you to consult a healthcare professional quickly.
How can you limit the risks?
The Culex mosquito is widely present in mainland France and is mainly active in the evening and at night. To limit bites, several simple steps are recommended: wear covering and loose clothing at the end of the day, install mosquito nets on windows, and use, if necessary, repellents on exposed skin areas. It is also advisable to limit stagnant water around homes by regularly emptying buckets, watering cans, and other containers that could serve as breeding grounds for larvae.
The ARS, for its part, continues to monitor the situation with health authorities and
animal health actors. For the general public, vigilance mainly relies on preventing mosquito bites and consulting a healthcare professional if symptoms appear. Nighttime mosquito control operations have been underway for several days in Lyon and the surrounding area.