West Nile virus cases in France are rising rapidly, with 117 confirmed infections reported in Metropolitan France as of September 21, according to a report by Santé publique France. This number marks a significant increase of 25 cases from the previous week and is expected to set a new record for the year. In 2025, the country saw a total of 62 cases from early May to late November, with five deaths attributed to the virus. The virus, which is typically found in the Mediterranean region, is now spreading beyond its traditional range. This year, outbreaks have been reported in several regions, including Provence-Alpes-Côte d'Azur, Occitanie, Île-de-France, and others, some of which are experiencing the virus for the first time. Human infections have also been detected in several departments that previously had no reported cases, indicating a broader geographic spread. West Nile virus is transmitted to humans through the bite of Culex mosquitoes that have previously fed on infected birds. Most people infected with the virus either show no symptoms or experience mild flu-like illness. However, in about 1% of cases, the virus can cause severe neurological complications, such as encephalitis or meningitis, which can be life-threatening, particularly for the elderly or those with weakened immune systems. There is currently no vaccine or specific treatment available for human infections. Across Europe, nearly 1,500 cases of West Nile virus have been reported since the start of the mosquito season, with Italy and Greece recording the highest numbers, according to the European Centre for Disease Prevention and Control. Experts suggest that the spread of the virus is being driven by factors such as changes in wetland areas, migratory bird movements, climate change, and the increasing presence of vector mosquitoes in northern regions. In addition to West Nile virus, France has also seen a rise in cases of chikungunya and dengue, both transmitted by tiger mosquitoes. These diseases have resulted in 96 autochthonous cases in Metropolitan France since early May, in addition to 562 imported cases. The spread of tiger mosquitoes outside their traditional tropical and subtropical habitats is linked to climate change and urbanization, which have created new environments conducive to their survival and proliferation.