Italian health authorities have documented evidence that rising temperatures and extended warm seasons are facilitating the geographic expansion of West Nile virus transmission across the country, with cases occurring during increasingly longer periods throughout the year.
Italy has recorded more than 650 West Nile infections so far this year, representing approximately half of all cases reported across Europe during the same timeframe. Antonino Bella, a researcher at Italy’s National Institute of Health, noted that elevated temperatures associated with climate change enable mosquitoes to reproduce more rapidly and lengthen the period of virus transmission, thereby increasing the likelihood that infected mosquitoes will transmit the virus to human populations. The virus became endemic in Italy starting in 2020, when case numbers began rising significantly, and is now detected routinely during summer and early fall months. While approximately 80 percent of infected individuals display no symptoms and most others experience mild flu-like illness, severe neurological complications can develop in a small proportion of cases, particularly among elderly individuals and those with pre-existing medical conditions.
The current year’s case totals align with patterns observed in recent seasons, though the potential for transmission to extend into November due to warmer conditions represents a notable development. Regions previously spared from significant West Nile activity are increasingly documenting infections, indicating gradual territorial expansion of the virus throughout Italy. The Netherlands reported more than two dozen cases this year, marking the country’s first recorded transmissions since 2020, along with several deaths according to its public health institute.
Experts from northern European countries are examining Italy’s surveillance and research infrastructure to prepare for potential virus establishment in their own regions. Marc-Alain Widdowson, head of the Pandemic Threats, Communicable Diseases, and AMR Division at the World Health Organization’s Europe office, acknowledged that extended mosquito seasons resulting from warming temperatures will likely facilitate virus expansion into additional countries, while noting that climate change represents one factor among multiple contributing elements including biodiversity loss and land-use modifications.
The European Center for Disease Prevention and Control warned in June that Europe’s warming trend, characterized by more frequent and severe heat waves, flooding, and lengthened summers, creates increasingly favorable conditions for invasive mosquito species including Aedes albopictus and Aedes aegypti, the latter known to transmit multiple arboviruses. Aedes albopictus established populations have expanded from eight European countries affecting 114 regions one decade ago to 13 countries encompassing 337 regions currently.
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