West Nile virus (WNV) is primarily transmitted by mosquitoes and can infect both animals and humans. Symptoms range from mild fever to severe, often fatal, neurological complications. In the Netherlands, it has claimed one life—an autochthonous human case, meaning the individual contracted the infectious disease locally without having traveled to an affected area.
We spoke with Steven Van Gucht, Head of the Viral Diseases Service at Sciensano, the Belgian scientific institute for human, animal, and environmental health.
Are these the first autochthonous human cases in the Netherlands?
An initial autochthonous human case had already been detected in the Netherlands in 2020. Unfortunately, there has now been a fatality. The patient was an elderly man—I believe 80 or older. So, the virus has been circulating there for a bit longer than here. We also anticipated the emergence of this virus in Belgium, as it was already appearing in all our neighbouring countries.
What is the risk of mosquito-to-human transmission in Belgium?
The risk is real, particularly at this time of year, given the usual peak in human cases across several European regions during August and early September. Evidence of the virus circulating among birds indicates its presence in our environment, making transmission to humans possible. While the vast majority of infections are asymptomatic or mild, approximately 1% can lead to a severe neurological form of the disease.
Would you be surprised if an autochthonous (locally acquired) human case appeared in Belgium?
No, I wouldn’t be surprised. I hope the cases won’t be too severe, but I don’t expect large numbers. In my view, these will remain isolated, sporadic cases rather than the major outbreaks sometimes seen with other viruses.
How does the virus circulate and how is it transmitted?
West Nile virus is not transmitted between people.
It is primarily transmitted by *Culex* mosquitoes, which are found here. Birds serve as the virus’s main reservoir. Mosquitoes become infected by biting infected birds and can subsequently transmit the virus to humans or horses. Humans are accidental hosts and play no significant role in transmission.
So, several factors come into play regarding the virus’s ecology. In that sense, it is less contagious than diseases like measles or influenza, which spread rapidly between humans; that is not the case here.
What are the symptoms? Is there a treatment or vaccine?
Most infections go unnoticed (in 80% of cases) or cause a flu-like illness characterised by fever, headaches, and muscle pain. In about 1% of infections, severe neurological complications—such as meningitis or encephalitis—can occur. This happens when the virus invades the brain or spinal cord. Naturally, this leads to more serious symptoms, such as paralysis, tremors, or a reduced level of consciousness.
To date, there is no specific antiviral treatment or vaccine available for humans. While a highly effective vaccine exists for horses, it has unfortunately never been developed for human use.
This virus is spreading northward. Is there a link to global warming?
It is highly likely that global warming is contributing to the virus’s spread into Northern Europe. Higher temperatures foster mosquito development and activity, and also allow the virus to multiply more rapidly within the mosquito. More virus means more transmission.
What are your recommendations for people in Belgium?
It is recommended to minimise mosquito bites, especially in the late afternoon and evening: wear protective clothing, use an appropriate repellent, and—whenever possible—sleep in a room protected by mosquito nets or windows fitted with screens.
Hospitals need to be on high alert to the possibility of West Nile virus infection in patients presenting with compatible neurological symptoms. A year ago, most doctors wouldn’t have even heard of the virus, let alone thought it.
A comms memo has been issued to all general practitioners and hospitals in Belgium.