West Nile virus confirmed in a horse in the Netherlands
West Nile virus (WNV) has been confirmed in a horse in the Netherlands. The investigation into WNV in a horse located in the province of Zuid-Holland was initiated following a report of clinical signs consistent with West Nile fever submitted to Royal GD. After Royal GD confirmed the viral infection, the Netherlands Food and Consumer Product Safety Authority (NVWA) collected an official sample. Wageningen Bioveterinary Research, the National Reference Laboratory for WNV, confirmed the presence of the virus. The sample has been sent to the European Reference Laboratory, ANSES, for confirmation. The results of this analysis are not yet available.
Symptoms in horses
In most horses, infection with WNV does not result in visible clinical signs associated with West Nile fever. When symptoms do occur, they are often mild, such as fever, lethargy or reduced appetite. In some cases, neurological signs may develop, for example impaired coordination. In a small number of cases, these symptoms become so severe – ranging from stiffness to paralysis – that euthanasia is required.
Infection with West Nile virus is a notifiable disease (Category E). Notification has no direct consequences for the horse or its owner. Horses can be protected against WNV infection through annual vaccination.
WNV detected in a song thrush
In addition to the WNV infection in the horse, the virus has also been detected in a song thrush captured and sampled in the province of Utrecht at the end of July. The bird was caught as part of the wild bird surveillance programme carried out by Erasmus MC. It was a young bird that could not have become infected through migration. Genetic analysis showed that the virus is closely related to the West Nile virus detected in mosquitoes and dead birds in the Netherlands in 2025.
Virus transmission
West Nile virus circulates in birds, in which the virus can multiply. Mosquitoes can then transmit the virus from birds to horses and humans. Horses and humans are considered dead-end hosts, meaning they do not transmit the virus further. As a result, horses and humans cannot infect each other with WNV.
