Italian health officials report that increasing temperatures and extended warm seasons are facilitating the spread of West Nile virus across the country. To date, Italy has documented more than 650 infections this year, representing approximately half of all cases identified throughout Europe.
“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).
Since the virus became endemic in Italy in 2020, it has been reported annually during the summer and early autumn months. While roughly 80% of infected individuals remain asymptomatic and most others experience only mild flu-like symptoms, severe neurological complications can arise in a small subset of patients, particularly among older adults and those with preexisting health conditions.
Experts note that current case numbers are consistent with recent years, yet warmer conditions are lengthening the transmission window, sometimes into November. Regions previously unaffected by the virus are increasingly reporting infections, indicating a gradual geographic expansion within the country.
Italy’s extensive surveillance network, which monitors mosquitoes, bird populations, blood donors, and human cases, contributes significantly to its high detection rates. This comprehensive approach has attracted international interest; a Belgian research team visited the ISS last May to study Italy’s monitoring systems.
Neighboring nations are witnessing similar shifts. The Netherlands reported more than two dozen cases and several deaths this year, marking its first locally acquired infections since 2020. Marc-Alain Widdowson, who leads the Pandemic Threats and Communicable Diseases division at the WHO Europe office, emphasized that warming weather is undeniably expanding the replication period for both the virus and its vectors.
“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,” Widdowson said.
The European Center for Disease Prevention and Control (ECDC) highlighted in June that changing land use, biodiversity loss, and a warming climate are creating favorable conditions for invasive mosquito species. Notably, the Aedes aegypti mosquito, which transmits dengue, yellow fever, Zika, and West Nile viruses, has been established in Cyprus since 2022 and poses a potential risk to other European countries.
Similarly, the range of the Aedes albopictus mosquito has expanded significantly. Ten years ago, it was present in eight European countries across 114 regions; this year, the ECDC reports it is established in 13 countries and 337 regions.
I wonder if travel insurance will soon exclude West Nile infections acquired in Southern Europe during extended summer trips.
Six hundred fifty cases and people are still complaining about heatwaves instead of taking this seriously. Wake up call if you will.
The surveillance data from Italy is impressive, but let’s not ignore that 80% asymptomatic rate masks the true scale of exposure in the population.
Does anyone know if the UK is seeing similar trends? The news focuses on Italy, but I heard cases are creeping north too.
It’s terrifying to see the mosquito season last until November now. My grandmother is high risk, and we are staying indoors more every year.