West Nile Virus: Why Cases Are Rising in Europe
The transmission season began earlier in several European countries. The virus circulates between birds and mosquitoes, while warmer conditions lengthen the period of risk.
West Nile virus is advancing in several parts of Europe as the mosquito season enters its most active phase. On 24 July 2026, the World Health Organization called on countries to strengthen surveillance and public information.
By 22 July, Greece had recorded 21 confirmed human cases, including 14 reported in the previous week alone. Italy had reported the same number across 17 separate areas. Locally acquired infections were also reported in North Macedonia, Romania and Spain.
These figures remain modest at continental scale. Their main significance is that transmission is already established and can evolve quickly during summer.
A cycle that does not rely on humans
- A mosquito, often of the Culex genus, bites a wild bird carrying the virus.
- It then transmits the virus to another bird, a horse or a human.
- In humans, the amount of virus in the blood is generally too low to infect another mosquito.
- The cycle therefore stops: the disease does not spread through ordinary person-to-person contact.
Humans are an incidental host. Rare transmission has nevertheless been documented through blood transfusion, organ transplantation, pregnancy or breastfeeding, which is why blood donations are secured in affected areas.
About 70% to 80% of infected people develop no symptoms. Others experience fever, headache, fatigue, muscle pain, nausea or a rash.
About one infection in 150 progresses to severe disease affecting the central nervous system, such as meningitis or encephalitis, with risk increasing with age and certain chronic conditions.
It changes the context but does not explain it alone. Temperature affects mosquito activity, reproduction and the time the virus needs to multiply inside the insect. Hotter summers and longer mild seasons create more favourable days. But infected birds, rainfall, standing water and land use also matter. An apparent increase can also reflect better detection or faster reporting.
Monitor birds to protect people
The European Centre for Disease Prevention and Control publishes a weekly update on virus circulation. Authorities combine several signals: human cases, equine infections, unusual bird mortality, mosquito trapping and laboratory analysis. This approach can detect local circulation before many severe cases appear.
There is currently no licensed human vaccine and no specific antiviral treatment. Care focuses on relieving symptoms and supporting vital functions in severe cases.
Wear covering clothing, use suitable insect repellent, install mosquito screens and, above all, remove standing water around the home. Plant saucers, buckets, gutters and uncovered tanks are breeding sites. High fever accompanied by a stiff neck, confusion, tremors or muscle weakness warrants prompt medical attention.