West Nile Virus Cases Rise Across Europe as Warmer Weather Extends Mosquito Season

West Nile virus infections are being detected across a growing number of European regions this year, with health authorities monitoring an increase in mosquito-borne disease activity during the 2026 transmission season.

Italy has recorded the largest number of locally acquired cases so far, while infections have also been reported in countries including Greece, Spain, Romania, France, the Netherlands and Belgium. European health officials say the situation highlights the importance of mosquito surveillance, public awareness and preventive measures as warmer conditions create more favourable environments for mosquito activity.

According to the European Centre for Disease Prevention and Control (ECDC), 1,482 locally acquired human cases of West Nile virus had been reported across 16 European countries by 17 September 2026. Italy accounted for 652 of those cases. The figures are based on cases reported to European surveillance systems and may be updated as national authorities revise their data.

What is West Nile virus?

West Nile virus is an infection mainly transmitted through the bite of an infected mosquito. Mosquitoes acquire the virus when they feed on infected birds and can subsequently transmit it to humans and other animals.

The virus has been present in different parts of Europe for many years, but its geographical distribution and seasonal activity can vary considerably from one year to another.

Most people infected with West Nile virus do not develop noticeable symptoms. When symptoms do occur, they can include fever, headache, tiredness, muscle aches, nausea and, sometimes, a skin rash.

In a small proportion of infections, however, the virus can affect the central nervous system. This can result in conditions such as encephalitis or meningitis, which require urgent medical attention.

The ECDC's September 2026 surveillance report said there was no indication at that point of increased disease severity among human cases in Europe, despite the substantial level of virus circulation.

Italy remains at the centre of the outbreak

Italy has reported more West Nile virus infections than any other European country during the 2026 season.

The Italian National Institute of Health, known as the Istituto Superiore di Sanità, reported 657 confirmed human infections in its 10 September update. Of these, 345 were classified as neuro-invasive infections, while 224 were cases of West Nile fever. The report also recorded 51 deaths among confirmed cases at that point.

The Italian figures are not necessarily identical to those published by European surveillance authorities because national and European reporting systems can have different update schedules and case classifications. Authorities also revise figures as new information becomes available.

Italy has developed an extensive surveillance system that monitors human infections as well as virus circulation in mosquitoes, birds and other animals. This helps authorities identify areas where transmission is occurring and respond to new infections.

West Nile virus has become an established seasonal health concern in parts of Italy. Cases can appear during the warmer months and continue into the autumn, depending on local weather conditions and mosquito activity.

Why are warmer temperatures important?

Researchers and public health officials have been examining the connection between changing environmental conditions and mosquito-borne diseases.

Antonino Bella of Italy's National Institute of Health told the Associated Press that higher temperatures associated with climate change can help mosquitoes reproduce and extend the period during which virus transmission can occur. He also stressed that climate change is not the only factor responsible for the spread of West Nile virus.

Other factors include rainfall, flooding, suitable habitats, the availability of mosquito species capable of carrying the virus, bird populations and human movement.

The ECDC has similarly warned that changing environmental conditions are influencing the landscape of mosquito-borne diseases in Europe. The agency said in August that West Nile virus was continuing to spread into new regions and that invasive mosquito species were becoming established in additional parts of Europe.

This does not mean that every warm summer will automatically result in a major outbreak. Instead, warmer conditions can create circumstances in which mosquitoes survive, reproduce and remain active for longer periods.

More countries are reporting infections

The expansion of West Nile virus activity is not limited to Italy.

The ECDC reported locally acquired infections in 16 European countries by 17 September. Greece had recorded 355 cases, followed by Spain with 114, Romania with 91 and France with 81.

The Netherlands had reported 29 cases, while Croatia, Cyprus, Belgium, Austria, Germany, Hungary, Albania and Kosovo had also reported locally acquired infections.

The Netherlands is particularly notable because its 2026 infections represent the country's first reported human West Nile virus cases since 2020, according to the joint ECDC and European Food Safety Authority surveillance report.

Health authorities are therefore paying close attention to areas where the virus has previously been uncommon or absent.

What symptoms should people know about?

Many people infected with West Nile virus have no symptoms at all. Others may experience a mild illness resembling flu.

Possible symptoms include:

• Fever
• Headache
• Muscle aches
• Tiredness
• Nausea
• Vomiting
• Occasionally, a skin rash

In rare cases, the infection can become more serious and affect the brain or nervous system.

Warning signs of serious neurological illness can include confusion, severe weakness, seizures, difficulty speaking, loss of consciousness or other sudden neurological changes. The NHS advises that serious symptoms associated with encephalitis require urgent hospital assessment.

Anyone who develops concerning symptoms after spending time in an area where West Nile virus is circulating should seek medical advice and mention their recent travel or mosquito exposure.

How can people reduce the risk?

There is no need for the public to panic, but sensible mosquito precautions can reduce exposure.

Health authorities generally recommend using insect repellent when appropriate, wearing clothing that covers the arms and legs, and using window screens or air conditioning where available.

People should also avoid leaving standing water around homes and gardens where mosquitoes can breed. Items such as buckets, plant containers and other outdoor objects can collect water and provide breeding sites.

Extra care can be useful during periods of high mosquito activity, particularly around dawn and dusk when some mosquito species are more active.

What happens next?

European surveillance authorities are continuing to monitor West Nile virus activity as the 2026 season progresses.

The ECDC reported that transmission usually peaks during August and early September, but cases can continue to appear later in the year. Earlier ECDC surveillance has shown that the timing of the transmission season can vary between countries and years.

The latest figures demonstrate that West Nile virus is an established mosquito-borne infection in several parts of Europe, while also showing why surveillance remains important in areas where local transmission has only recently appeared.

For travellers, the message is relatively straightforward: be aware of mosquito activity, take practical precautions and seek medical advice if significant symptoms develop after possible exposure.

Sources

• European Centre for Disease Prevention and Control, West Nile virus surveillance, 2026.
• European Centre for Disease Prevention and Control and European Food Safety Authority, September 2026 West Nile virus surveillance report.
• Istituto Superiore di Sanità, Italy, 2026 West Nile virus surveillance data.
• NHS, information on encephalitis and serious neurological symptoms.

Disclaimer: This article is for general information only and is not medical advice. West Nile virus risk varies by location and circumstances, and official case numbers can change as surveillance data are updated. If you develop concerning symptoms or are worried about a possible infection, contact a qualified healthcare professional or the appropriate local health service.