Italy sees mosquitos spread the West Nile virus further and longer as Europe warms

Italian health authorities see evidence that rising temperatures and longer warm seasons are helping mosquitoes spread West Nile virus across a wider area during more months of the year.

More than 650 infections have been reported in Italy so far this year, accounting for about half of all cases recorded in Europe, according to local health authorities.

“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,” said Antonino Bella, a researcher at Italy’s National Institute of Health (ISS).

Experts say this year’s case numbers are broadly in line with recent seasons.

But warmer temperatures favour mosquito reproduction and can mean the transmission season sometimes lasts as late as November, Bella explained. Areas once largely unaffected are increasingly reporting infections, reflecting a gradual expansion of the virus across the country.

The Netherlands this year has reported more than two dozen West Nile cases, the first since 2020, as well as several deaths, according to its public health institute.

“There’s no doubt that warming weather will expand the period of replication for the virus and the vector in more countries,” said Marc-Alain Widdowson, who leads the Pandemic Threats, Communicable Diseases, and AMR Division at the World Health Organisation’s Europe office.

Experts note 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.

“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.

In June, the European Centre for Disease Prevention and Control (ECDC) warned that because Europe is experiencing a warming trend — with heatwaves and flooding becoming more frequent and severe, and summers getting longer and warmer — the conditions are more favourable for invasive mosquito species such as Aedes albopictus and Aedes aegypti.

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.

A decade ago, the Aedes albopictus mosquito was established in eight European countries, with 114 regions affected. This year, the mosquito is established in 13 countries and 337 regions, the ECDC said.