West Nile Emergence unit

Activation of a Level 1 Emergency unit

On 21 August 2025, in response to the epidemiologic situation regarding WNV in mainland France, ANRS MIE activated a Level 1 Emergency Unit as part of a dedicated multi-level procedure providing a proportionate response to health crises. Several actions have been taken:

– online issue of a monthly scientific literature review,

– the organisation of a research meeting dedicated to WNV with the Arbo-France network.

It includes (soon):

• a brief overview of the epidemiology, virology, clinical features and risk assessment of the disease,
• recommendations for diagnosis, prevention and care,
• recent scientific articles published in peer-reviewed journals,
• an update on the current pipeline of drug development, clinical trials and technologies aimed at preventing and treating the disease,
• an overview of current clinical trials,
• official reports from health agencies and press releases from reliable sources.

Epidemiological situation of WNV infection

Epidemiological situation in Europe

In 2024, 19 European countries reported 1,436 human locally-aquired cases of WNV infection, including 235 deaths, mainly reported in Italy (455 cases and 21 deaths) and Greece (217 cases and 34 deaths).¹

From the beginning of the year to 22 August 2025, nine European countries reported human cases of WNV infection: 2 in Albania, 1 in Bulgaria, 2 in Hungary, 5 in Romania, 15 in France, 37 in Greece, 9 in Serbia, 1 in Spain and 267 in Italy.²

Epidemiological situation in mainland France

In 2024, 38 cases of loqually-acquired WNV infection were reported in the Provence-Alpes-Côtes d’Azur, Occitanie and Nouvelle-Aquitaine regions: 24 cases in Var, 9 in Hérault, 3 in Gard, 1 in Gironde and 1 in Pyrénées-Atlantiques. With 39 cases, the toll for 2024 was one of the highest, close to that of 2023, and significantly higher than those of 2022 (6 cases) and 2021 (no cases). Since 2021, WNV infection is a notifiable human disease at the EU level, thereby strengthening its surveillance.³

As of 27 August 2025, 15 cases of locally-acquired WNV infection have been reported in mainland France, including 10 cases in Provence-Alpes-Côte d’Azur, 2 in Île-de-France, 1 in Corsica and 2 in Occitanie.⁴

The Île-de-France episode affected two patients with no history or risk factors, both of whom developed a neurological form of the disease. Neither of these individuals received any treatment. They were discharged unharmed and without sequelae after a few days in hospital. While neurological forms are generally rare (< 1% of cases) in WNV infection, they affected nearly 40% of patients (6/15) in 2025.

Bibliography

1. Historical data by year – West Nile virus seasonal surveillance, 2024. https://www.ecdc.europa.eu/en/west-nile-fever/surveillance-and-disease-data/historical  (accessed on28/08/2025)
2. Weekly updates: 2025 West Nile virus transmission season. https://www.ecdc.europa.eu/en/west-nile-fever/surveillance-and-disease-data/disease-data-ecdc  (accessed on 28/08/2025)
3. Bilan de la surveillance humaine du virus West Nile (ou virus du Nil Occidental) en France hexagonale en 2024. Saint-Maurice : Santé publique France, 7 p. Mai 2025.
4. Santé publique France : Chikungunya, dengue, zika et West Nile en France hexagonale. Bulletin de la surveillance renforcée du 20 août 2025. https://www.santepubliquefrance.fr/maladies-et-traumatismes/maladies-a-transmission-vectorielle/chikungunya/documents/bulletin-national/chikungunya-dengue-zika-et-westènile-en-france-hexagonale.-bulletin-de-la-surveillance-renforcee-du-20-aout-2025 (accessed on  28/08/2025)