The West Nile virus affects several European regions every year. In France, it is regularly detected along the Mediterranean coast but has now also been identified in many other regions. Its epidemiology is evolving, influenced by various factors, particularly environmental and climatic ones.

Surveillance of the West Nile virus

The West Nile virus surveillance system is multidisciplinary, based on a “One Health” approach. It comprises four components: human surveillance, equine veterinary surveillance, avian surveillance (carried out primarily by the Directorate General for Food, the National Agency for Food, Environmental and Occupational Health Safety, and the French Office for Biodiversity), and entomological surveillance (activated in the event of viral circulation). Healthcare professionals, the Regional Health Agencies (ARS), and the National Reference Center for Arboviruses participate in this effort.

Human Surveillance of the West Nile Virus

Surveillance of the West Nile virus is based on mandatory reporting, effective as of 2021. In its opinion dated February 7, 2020, the HCSP recommended that West Nile virus infection be added to the list of notifiable diseases.

The National Reference Center for Arboviruses also contributes to surveillance by providing expertise to microbiologists and clinicians for diagnosis and by immediately reporting any confirmed case in mainland France or the overseas departments to the ARS and Santé publique France.

Mandatory reporting applies to all cases of West Nile virus infection that are biologically documented (probable or confirmed; definitions below). The report must be sent immediately to the ARS surveillance and alert unit by any appropriate means (phone, fax, email) and then submitted using the mandatory reporting form.

Reporting criteria: any biologically confirmed case, regardless of symptoms.

Definition of cases to be reported and notified

• Confirmed case:
  • Detection of the viral genome in a biological sample
  • Isolation of WNV by culture in a biological sample
  • Detection of anti-WNV IgM in cerebrospinal fluid (CSF)
  • Seroconversion or a fourfold increase in IgG levels confirmed by seroneutralization
• Probable case:
  • Detection of IgM in serum (ELISA)
  • Seroconversion or a fourfold increase in IgG levels in two consecutive samples

Although all biologically confirmed infections must be reported, monitoring neuroinvasive cases is the most effective way to identify epidemiological trends of the virus. This surveillance relies on clinicians and hospital laboratories, who are trained in diagnosis and reporting at the start of the season. Surveillance data from all relevant sources—including humans, horses, birds, and mosquito vectors—help monitor the virus’s spread throughout the country.

Learn more about West Nile virus surveillance in animals:

• List of the latest equine disease alerts | Respe
• Interactive map from ESA (Animal Health Epidemiological Surveillance)

Surveillance partners

National Reference Center for Arboviruses

• CNR Metropolitan Coordinator | Contacts
  • INSERM
  • Scientific Director: Prof. X. de Lamballerie
  • Scientific Directors: N. Ayhan, L. Pezzi, R. Klitting
  • IRBA Marseille
  • Director: G. Grard
  • Deputy Director: G. Durand
  • Address: IHU Méditerranée-Infection, 1st Floor – Laboratory 114, 19-21 Boulevard Jean Moulin, 13005 MARSEILLE
  • Secretariat: +33 (0)4 13 73 21 81 - Secretariat Fax: +33 (0)4 13 73 21 82
• CNR Affiliated Laboratory, Antilles-Guyana Region
  • Pasteur Institute of French Guiana
  • Director: D. Rousset
  • Address: Pasteur Institute of French Guiana, Virology Laboratory, 23 Pasteur Avenue - P.O. Box 6010 - 97 306 Cayenne Cedex - French Guiana
  • Lab: 05 94 29 58 27 - Office: 05 94 29 58 16 - Fax: 05 94 29 58 09
• CNR Affiliated Laboratory, Indian Ocean Region
  • Saint Denis University Hospital, Réunion
  • Director: N. Traversier
  • Address: Saint-Denis University Hospital, Réunion (Félix Guyon), Microbiology Laboratory, Allée des Topazes - CS11021 - 97405 Saint-Denis Cedex
  • Secretariat: 02 62 90 62 60 - Fax: 02 62 90 53 38 or 02 62 90 50 54

Preventive Measures Against the West Nile Virus

Santé publique France provides information to healthcare professionals, local authorities, and the general public on measures to prevent mosquito-borne transmission.