Netherlands reports first locally acquired infections since 2020, with several deaths

Italy has emerged as the focal point of West Nile virus activity in Europe, with more than 650 infections recorded so far in 2026 — roughly half of the continent’s reported cases — as researchers connect the surge to warmer temperatures and a lengthening mosquito season. The figure underscores Italy’s outsized share of European cases this year, drawing attention from health agencies across the continent.

“Higher temperatures linked to climate change help mosquitoes reproduce and extend the transmission season, increasing the chances that infected mosquitoes will spread the virus to people,” Antonino Bella, a researcher at Italy’s National Institute of Health (ISS), told The Associated Press.

West Nile has been classified as endemic in Italy since 2020, when cases began to surge, and is now reported every summer and early fall. Experts told the AP that this year’s case numbers are broadly in line with recent seasons. About 80 percent of infected people develop no symptoms, while most others experience a mild flu-like illness. Severe neurological complications occur in a small minority of cases, mainly among older adults and people with underlying health conditions.

The spread has been geographically uneven but persistent. Bella explained that warmer temperatures favor mosquito reproduction and can mean the transmission season sometimes lasts as late as November. Areas once largely unaffected are increasingly reporting infections, reflecting a gradual expansion of the virus across the country.

The pattern is no longer confined to Italy. The Netherlands this year has reported more than two dozen West Nile cases — its first since 2020 — as well as several deaths, according to its public health institute. A Belgian research team visited the ISS last May to study Italy’s surveillance system after Belgium began recording locally acquired cases.

Marc-Alain Widdowson, who leads the Pandemic Threats, Communicable Diseases, and AMR Division at the World Health Organization’s Europe office, said warming weather is widening the window for transmission across the continent.

“There’s no doubt that warming weather will expand the period of replication for the virus and the vector in more countries,” Widdowson said. “You’ve got to be careful not to say that climate change is all of it, but certainly a warming climate means that we have a longer mosquito season, so that the vectors can survive for longer. Warm temperatures also mean that the virus itself will survive better,” he added.

“There are definitely trends which we think are contributing to increased activity,” Widdowson said, citing a warming climate, loss of biodiversity and changes in land use. A longer mosquito season creates more opportunities for transmission, he added, while declines in bird diversity may favor species that are efficient reservoirs of the virus.

Experts noted that Italy’s extensive monitoring network — which tracks mosquitoes, birds, blood donors, and human infections — also helps explain why the country detects so many cases. The surveillance system has become a reference point for other European countries confronting their own outbreaks.

In June, the European Centre for Disease Prevention and Control (ECDC) warned that Europe’s warming trend, marked by more frequent and severe heat waves and flooding and longer, hotter summers, is creating conditions more favorable for invasive mosquito species. The agency specifically flagged Aedes albopictus and Aedes aegypti as species of concern.

A decade ago, Aedes albopictus was established in eight European countries, with 114 regions affected. This year, the mosquito is established in 13 countries and 337 regions, according to the ECDC. Aedes aegypti — known to transmit dengue, yellow fever, chikungunya, Zika, and West Nile viruses — has been established in Cyprus since 2022 and may spread to other European countries, the agency said.