Five New Suspected West Nile Cases in Belgium
Belgian regional health authorities reported five new suspected human cases of West Nile virus (WNV) infection on Thursday — three in Flanders and two in Brussels — bringing the total number of (highly) probable cases in the two regions to ten. Officials stressed that none of those affected is seriously ill.
According to VRT NWS, the Flemish health department Departement Zorg now counts eight (very) probable human cases, while the Brussels health authority Vivalis reports two. The announcement follows the first-ever locally acquired human infections in Flanders, confirmed on 11 September, and comes amid an unusually active West Nile season across Europe.
A First for Belgium
The new suspected cases mark a significant shift for a country that, until this year, had recorded the virus only in animals. “In total we now count 10 reported West Nile virus infections in Flanders and Brussels,” Joris Moonens of Departement Zorg said. “They are all people who have recovered, or are recovering. Nobody is seriously ill.”
In Flanders, the five probable cases announced late last week were followed by three further suspected infections, again in the provinces of Antwerp and Flemish Brabant. One person was hospitalised with neurological symptoms but is now recovering, and the virus was also detected in a horse in Limburg.
In Brussels, one of the two cases is a resident who is now in good health and no longer showing symptoms. The second is an Italian tourist who has since returned to Italy and displayed no acute symptoms.
No human cases have been reported in Wallonia, according to the regional agency AVIQ, or in the German-speaking Community. However, two birds tested positive in Wallonia between May and August.
An Expected Escalation
The cluster is not a surprise to health officials. When the first human cases were confirmed on 11 September, Anneleen De Sadeleer, a spokesperson for Departement Zorg, noted that “the fact that there are several infections at once can possibly be explained by the fact that the virus is circulating more strongly throughout Europe.”
That broader European picture is stark. By 26 August, 877 locally acquired human infections had been reported across 15 countries, most of them in Italy and Greece but also in France, Spain and Germany, according to European surveillance data cited by VRT NWS.
The most affected neighbouring country is the Netherlands. By 10 September, Dutch authorities had recorded 18 human infections and three deaths, with cases spread across Utrecht, North Brabant, North Holland, South Holland, Overijssel and Gelderland. The RIVM, the Dutch national institute for public health, reported that the number of infections had doubled in a single week, from nine to 18. The virus also infected 58 horses and 39 birds there, killing 23 of the birds.
In Belgium, the animal toll has been building since early August. As of 10 September, the Federal Agency for the Safety of the Food Chain (FAVV) had recorded 25 horse cases, with two animals euthanised, and several infected birds. FAVV spokesperson Hélène Bonte told Belga that the animal figures are expected to rise further as samples — including from birds in rescue centres — are still being tested.
How the Virus Spreads
West Nile virus circulates between birds and mosquitoes. A mosquito becomes a carrier after biting an infected bird and can then transmit the virus to humans and horses. Humans are an “epidemiological dead-end host” — they cannot pass the virus on through ordinary contact.
The clinical picture is reassuring for most people. Roughly 80 percent of those infected show no symptoms at all. About 19 percent develop a mild, flu-like illness with fever, headache, muscle pain and fatigue, sometimes accompanied by a rash or swollen lymph nodes. In fewer than 1 percent of cases — typically among the elderly and immunocompromised — the virus attacks the nervous system, causing encephalitis or meningitis. There is no specific treatment and no vaccine; care focuses on managing symptoms with painkillers.
Belgian officials have been quick to stress that the risk to the general public remains low. Virologist Steven Van Gucht of Sciensano told De Standaard and Het Belang van Limburg that while the appearance of the virus in Belgium is new, “there is no reason for panic.” He warned, however, that “the time when mosquitoes were merely annoying is over.”
The Climate Signal
Scientists place the Belgian outbreak within a broader, climate-driven expansion of the disease. Research by the VUB and ULB in Brussels has demonstrated a robust link between climate change and the spread of West Nile virus in south-eastern Europe, with high spring and summer temperatures, summer droughts and warm winters all favouring transmission.
“Unlike corona, this is a virus where climate factors are very important for possible infections,” VUB climate scientist Wim Thiery told VRT NWS. “Currently we mainly see the Mediterranean region and the Balkans emerging as red zones, but it is quite possible that in the future this will advance further north toward our regions.”
Diana Erazo, lead author of the VUB-ULB study, said the findings also point to “a recent and dramatic increase in the number of people at risk of exposure,” driven partly by rising population density but with climate change remaining “a crucial factor.”
Thiery framed the trend bluntly: “This is the face of climate change. Alongside escalating climate extremes, the emergence of tropical diseases in Europe is unfortunately one of the many logical consequences of our addiction to oil, coal and gas.”
Adding to the concern, virologist Leen Delang of KU Leuven has shown that Belgian mosquitoes — specifically the common house mosquito, Culex pipiens — are capable of becoming infected and transmitting the virus. That finding confirms that local transmission is not merely a theoretical risk.
What to Watch
Health authorities are urging vigilance rather than alarm. Doctors have been asked to stay alert for symptoms, and residents in affected provinces — along with care homes — have been informed. Sciensano and provincial authorities are monitoring the situation.
The public is advised to avoid mosquito bites by wearing long sleeves and trousers at dusk, using repellent and screens, and removing standing water from gardens and terraces every week. The measures are recommended until the end of the Belgian mosquito season, expected to run until the end of October. The federal health authority has published a dedicated FAQ on the virus.
Several questions remain open. Because confirmation tests on the latest suspected cases are still running, the final tally may shift. The bigger uncertainty is whether this summer represents a permanent northward shift of the virus into Belgian territory — a scenario scientists say is plausible — or a transient spike in an exceptionally warm year. With the season not yet over, the coming weeks will show whether the caseload stabilises or continues to climb.