On July 29, 2025, a first indigenous case of infection by the West Nile virus was confirmed in mainland France. The person concerned, identified in the Provence-Alpes-Côte d’Azur region, had presented the first symptoms from July 15. This case is part of an increased circulation dynamic of the virus observed since 2010 in the French Mediterranean. On a European scale, Greece, Italy and Romania have also reported human cases since the beginning of the year, according to the European Center for Disease Prevention and Control (ECDC).
West Nile: Role of mosquitoes and climate change
The West Nile virus is the cause of Western Nile fever, a disease transmitted to humans by mosquitoes of the genre Culexassets in mainland France from May to November. These mosquitoes contract the virus by pricking infected birds, which constitute the main reservoirs of the infection. The evolution of the migratory courses of these birds, influenced by climate change, contributes to the increase in cases observed since 2010 in the French Mediterranean. Human beings, just like some animals – especially horses – is only an accidental host of the virus.
In an opinion published in April 2024, the Sanitarian Risk Monitoring and Anticipation Committee (COVARS) ranked West Nile virus infection, alongside the major health risks for the next five years.
A reinforced surveillance system against the West Nile virus in France
To prevent the serious forms of the disease and secure products from the human body (blood donations, organ donations, etc.), France has set up a multidisciplinary monitoring device. This system combines the sectors of human health, animal health and entomologists (people studying insects). It involves health professionals, regional health agencies (ARS), health agencies, reference laboratories and expert centers.
The human component is based on the compulsory report of all confirmed cases, whether imported or indigenous. This system is reinforced by the automated transfer of the results of the main diagnostic laboratories and by increased awareness of health professionals during the mosquito activity period, from May 1 to November 30.