West Nile virus is circulating in Belgium: should residents be worried?

West Nile virus normally circulates between birds and mosquitoes, especially common Culex mosquitoes. An infected mosquito can occasionally pass it to a person or horse. Humans and horses are considered dead-end hosts: they generally do not carry enough virus in their blood to infect another mosquito and do not spread the disease through ordinary contact, the European Food Safety Authority explains.

The detections therefore show that infected mosquitoes have been active locally; they do not show that Belgium is experiencing a human outbreak. About 80% of infected people develop no symptoms, according to EFSA. Roughly one in five may experience West Nile fever, with complaints such as fever, headache, muscle pain, tiredness or a rash. Fewer than 1% develop disease affecting the nervous system, including meningitis or encephalitis. Older adults and people with weakened immune systems face the greatest risk of severe illness.

There is no human vaccine or virus-specific treatment. Most mild illness is managed with rest and symptom relief, while serious neurological disease requires hospital care. A person who develops fever after heavy mosquito exposure can contact a huisarts in Dutch-speaking services or a médecin généraliste in French-speaking services. Sudden confusion, marked muscle weakness, seizures, neck stiffness or loss of consciousness warrants urgent medical assessment. Residents should not try to diagnose West Nile fever from flu-like symptoms alone: many more common infections can look similar, and laboratory testing is needed.

The useful precautions are familiar and inexpensive. Departement Zorg advises covering exposed skin when mosquitoes are numerous, using an effective repellent such as one containing DEET, fitting insect screens and sleeping under a mosquito net where necessary. Repellent instructions matter, particularly for children, pregnant people and anyone combining repellent with sunscreen.

Householders can also interrupt mosquito breeding by emptying water from buckets, plant saucers, toys, tarpaulins and blocked gutters at least weekly. Rain barrels should be covered. In an apartment building, water collecting on a shared roof terrace or courtyard should be reported to the syndic; persistent nuisance or neglected public-space breeding sites can be raised with the local gemeente or commune. The relevant health information may appear under westnijlkoorts on Dutch-language portals and fièvre du Nil occidental on French-language ones.

These measures are worthwhile beyond West Nile virus because they also reduce bites from other mosquitoes. They should nevertheless remain proportionate: ordinary contact with birds, horses, neighbours or pets does not transmit the virus, and there is no public-health case for avoiding the Mechelen, Antwerp, Namur or Vilvoorde areas.

The federal response includes a precaution that may be more visible than the illness itself. Following the infected horse near Vilvoorde, FAMHP/AFMPS instructed Belgian blood establishments to ask whether donors live in, or recently spent a night in, Vilvoorde, Steenokkerzeel, Machelen, Zemst or Grimbergen. Relevant donations are screened because an asymptomatic infection can, rarely, be transmitted through blood products. The agency stressed that the measure protects recipients and is not evidence of a detected human case.

Anyone planning to donate should answer the blood service’s travel and residence questions accurately and consult the current rules of Rode Kruis-Vlaanderen, the Croix-Rouge de Belgique, La Transfusion du Sang or CHU UCL Namur. Screening arrangements can change as surveillance maps are updated, so the blood establishment’s instructions take precedence over older online advice.

Belgium’s experience fits a broader change in Europe rather than an isolated event. ECDC and EFSA recorded 245 locally acquired human cases and 12 deaths in Europe by 5 August 2026, mainly in Italy and Greece, while Belgium had reported an animal outbreak in Namur. The agencies expected further detections during August and September, the usual seasonal peak, although the number of reported human cases at that point remained below the ten-year average for the same period.

Warmer conditions can make mosquito transmission more favourable, but surveillance also changes what authorities find. Belgium’s targeted monitoring of wild birds revealed infections that would probably have passed unnoticed when no person became seriously ill. That distinction is important: more detections can reflect both genuine geographical spread and better observation.

The next questions are whether surveillance identifies human infection, whether infected animals appear in additional municipalities and whether the virus persists beyond a single season. Sciensano, the regional health administrations, FAVV/AFSCA and FAMHP/AFMPS are monitoring different parts of that picture. For now, Belgium has crossed from preparing for West Nile virus to documenting its local circulation, but not into a confirmed human outbreak. A little more attention to mosquitoes is justified; fear is not.