More than 650 West Nile virus cases have been recorded nationwide this year — around half of all infections logged across Europe — as health authorities link the trend to longer, hotter summers.
Italian health officials say rising temperatures are helping mosquitoes carry West Nile virus into new areas and across a longer stretch of the year. More than 650 infections have been recorded nationally so far in 2026, roughly half of all cases reported across Europe.
Antonino Bella, a researcher at Italy’s National Institute of Health (ISS), said warmer conditions linked to climate change help mosquitoes breed and extend the period during which the virus can spread, raising the odds that an infected mosquito passes it on to a person. West Nile has been considered endemic in Italy since 2020, when case numbers first began to climb, and is now expected as a seasonal presence each summer and into autumn. Around 80% of those infected show no symptoms at all, most others experience a mild flu-like illness, and only a small proportion — mainly older adults and people with existing health conditions — go on to develop serious neurological complications.
A longer season and a wider spread
Experts say this year’s overall case count is broadly in line with recent seasons, but the pattern is shifting: warmer weather can push the transmission season as late as November, and regions that had previously seen little or no activity are now reporting infections, pointing to a gradual spread of the virus across the country. Officials also credit Italy’s extensive surveillance network — which monitors mosquito populations, wild birds, blood donors and confirmed human cases — with why the country picks up so many infections relative to its neighbours.
Italy’s experience is now being studied further north. A Belgian research team visited the ISS in May to learn from the country’s surveillance model, after Belgium recorded its own locally-acquired cases. The Netherlands, meanwhile, has reported more than two dozen West Nile infections and several deaths this year, its first cases since 2020.
A wider European pattern
Marc-Alain Widdowson, who leads work on pandemic threats and communicable disease at the World Health Organisation’s Europe office, said a warming climate is extending the mosquito season across the continent, allowing both the insects and the virus itself to survive for longer, alongside factors such as biodiversity loss and land-use change.
The European Centre for Disease Prevention and Control warned in June that longer, hotter summers and more frequent heatwaves and flooding are creating more favourable conditions for invasive mosquito species, including Aedes albopictus and Aedes aegypti — the latter a carrier of dengue, yellow fever, chikungunya, zika and West Nile virus. The ECDC says Aedes albopictus, established in just eight European countries a decade ago, is now present in 13 countries and 337 regions.
