West Nile virus surveillance efforts further enhanced in 2025

Luxembourg remains free of West Nile virus for the moment, but the virus is getting closer and closer

• Clinical and Applied Virology
• Department of Infection and Immunity
• OH4Surveillance

In recent years, West Nile virus infections have emerged as an increasing public health concern across Europe. The virus is transmitted primarily between birds through bites from endemic mosquito species. Mosquitoes that feed on both birds and mammals can facilitate spillover to other hosts such as horses and humans. Most infections in humans are asymptomatic or mild, but in rare cases the virus can cause severe disease, including encephalitis or meningitis.

In 2025, West Nile virus has continued its geographic expansion in Europe. Indigenous human cases were detected in departments near Paris, indicating local transmission in the Île-de-France region. The virus was recorded for the first time in wild birds in Belgium. Also in 2025, the Netherlands reported their first West Nile outbreak in equids, adding to previous detections of the virus in mosquitoes, birds and humans documented since 2020.

While effective vaccines are available to protect horses against clinical disease, there are currently no licensed human vaccines; therefore, prevention is key. Systematic surveillance in animals remains an essential early warning tool to trigger appropriate preventive actions, such as awareness campaigns to minimize mosquito bites and screening of some blood product or organ donations.

The LIH, in partnership with the Luxembourg Veterinary and Food Administration (ALVA) and the Centre de Soins pour la Faune Sauvage in Dudelange, the Parc Merveilleux and the Nature and Forest Agency, has further expanded its West Nile virus surveillance program in wild birds in 2025. The number of samples tested more than doubled compared to the year before, highlighting the successful collaboration and the commitment of the partners to support animal and public health.

West Nile virus was not detected in Luxembourg in 2025, but Usutu virus – that shares epidemiological features with West Nile virus – was again identified. Its maintenance in the country is an indication that suitable conditions are present to support West Nile virus circulation upon introduction. It reiterates the necessity and operational reliability of the ongoing sentinel surveillance.

Disclaimer

West Nile virus surveillance is supported by co-funding from the European Union’s EU4Health programme under Grant Agreement Nr 101132473 OH4Surveillance.

Views and opinions expressed do not necessarily reflect those of the European Union or HaDEA. Neither the European Union nor the granting authority can be held responsible for them.