In 2026, France reported a record number of infections from the West Nile virus, affecting both humans and horses. By September 21, 2026, the country had recorded 117 human cases and more than 250 cases in horses, according to the bulletin from Santé publique France. Across Europe, over 1,500 cases had been identified, with nearly 80 deaths reported. The virus, which is spread by mosquitoes, has been a growing concern in recent years due to its ability to cause severe illness, particularly in vulnerable populations. The West Nile virus was first identified in 1937 in Uganda and is primarily transmitted by the common mosquito Culex pipiens. Birds are the main reservoir of the virus, and it was first recorded in Europe in the Camargue region of southern France in 1962-1963. A major outbreak occurred in Romania in 1996, and the virus later reached the United States in 1999, where it caused significant outbreaks in birds, horses, and humans. In 2018, the virus spread widely across western Europe, marking the largest epidemic in the region to date. The 2026 outbreak has seen the virus expand its geographic reach, with Italy and Greece accounting for more than half of the cases identified by early September. In France, 16 departments are affected, including several that reported their first cases this year, such as Aude, Seine-et-Marne, Drôme, and Rhône. The PACA region, which includes parts of the south of France, has been the most affected, with 39 human cases recorded. The virus typically remains active until November, and current weather conditions, which are favorable for mosquito activity, suggest the situation may worsen in the coming weeks. The West Nile virus is an arbovirus, meaning it is transmitted by arthropods such as mosquitoes. Unlike other arboviruses like dengue or chikungunya, it cannot be spread directly from person to person through mosquitoes. However, it can be transmitted through blood transfusions or organ transplants, as seen in two cases in France in 2025. The virus can lead to serious neurological complications, sometimes fatal, with less than 1% of infected individuals developing severe, neuro-invasive forms. These severe cases mainly affect the elderly and people with chronic illnesses. In 2025, France recorded its first five deaths linked to the virus, and by early September 2026, nearly 80 deaths had been recorded, with Italy bearing the heaviest toll, reporting more than 50 deaths. The spread of the virus is expected to increase further due to climate change, which extends the mosquito season, increases their lifespan, and alters their metabolism. Warmer temperatures and more frequent heatwaves and thunderstorms create conditions that are ideal for mosquito breeding, such as stagnant water. These factors contribute to the virus's increased transmission potential. To combat the spread, efforts are focused on monitoring the virus through the One Health approach, which involves tracking birds, horses, and mosquitoes. Until a human vaccine is developed, preventive measures such as eliminating stagnant water and using repellents are recommended to reduce the risk of infection.