West Nile virus (WNV) has been detected in a song thrush (Turdus philomelos) that was captured and sampled on 19 July 2026 at a bird-ringing site in the Utrecht region in the Netherlands. The bird was tested as part of a wild bird surveillance programme conducted by Erasmus MC and the Netherlands Institute of Ecology (NIOO-KNAW). Genetic analysis showed that the virus detected in the song thrush is closely related to the West Nile viruses found in Dutch mosquitoes and dead birds in 2025. Shortly after this detection, a West Nile virus infection was also confirmed in a horse in the province of South Holland (NVWA). Together, these findings indicate that infected mosquitoes are currently active and capable of transmitting the virus to birds, horses and humans.

West Nile virus

West Nile virus is transmitted by the common house mosquito (Culex pipiens). Infected mosquitoes can spread the virus to birds, horses and humans. Infected horses and humans cannot transmit the virus further, but they can become ill as a result of the infection.

Most people (around 80%) do not develop symptoms after infection. Approximately 20% experience mild symptoms such as fever, headache and muscle pain. A small proportion of infected people (around 1%) develop severe disease, including encephalitis or meningitis. The risk of severe illness is higher in older adults and people with underlying medical conditions. Horses can also become (seriously) ill following a West Nile virus infection.

Reducing the risk of mosquito bites

The detection of West Nile virus in a wild bird and a horse shows that the virus is currently circulating. However, the risk for humans becoming infected through a mosquito bite remains low. To reduce this risk even further, it is advisable to take measures to prevent mosquito bites, such as removing standing water around your home and protecting yourself against mosquito bites. More information and practical advice can be found here: Mosquitoes | RIVM.