Italian health authorities report that rising temperatures and extended warm seasons linked to climate change are contributing to the wider spread of West Nile virus across the country. As of 2026, more than 650 cases have been documented in Italy, representing about half of all West Nile infections reported in Europe this year, according to the National Institute of Health (ISS).

Researchers emphasize that higher temperatures create favorable conditions for mosquito reproduction and lengthen the period during which the virus can be transmitted. Antonino Bella, a researcher at the ISS, highlighted that these climatic changes increase the likelihood of infected mosquitoes passing the virus to humans. Since 2020, West Nile virus has become endemic in Italy, with cases emerging every summer and early fall. While approximately 80% of infected individuals show no symptoms, most others develop mild flu-like symptoms. Severe neurological complications are rare but can affect older adults and those with underlying health conditions.

This year’s infection rates are consistent with recent seasonal patterns, yet warmer weather has led to longer transmission periods, sometimes extending the risk into November. Areas previously unaffected are now reporting cases, signaling a gradual geographic expansion of the virus within Italy.

Italy’s experience serves as a reference for other European countries monitoring the disease’s spread. For instance, a Belgian research team visited the ISS to examine Italy’s surveillance methods after Belgium began reporting locally acquired cases. The Netherlands has recorded over two dozen West Nile cases in 2026—its highest since 2020—along with several related deaths, according to its public health institute.

Experts caution that although climate change is not the sole factor driving the increasing virus activity, it plays a significant role by extending the mosquito season. Marc-Alain Widdowson, who leads the World Health Organization’s Europe office division focusing on pandemic threats and communicable diseases, noted that warming weather enlarges the timeframe for both the virus and mosquito replication.

Italy’s comprehensive monitoring infrastructure, which includes surveillance of mosquitoes, birds, blood donors, and human cases, contributes to the country’s relatively high detection rates compared to other regions. Widdowson also pointed to environmental shifts, including biodiversity loss and changes in land use, as factors that may enhance virus transmission. A reduced diversity in bird species, for example, may favor those that serve as efficient virus reservoirs.

The European Center for Disease Prevention and Control (ECDC) has issued warnings about the broader European context, where warming trends are causing more frequent heat waves, flooding, and longer summers. These changes create ideal conditions for invasive mosquito species such as Aedes albopictus and Aedes aegypti, which are capable of transmitting a range of viruses including West Nile, dengue, and Zika. Since its establishment in Cyprus in 2022, Aedes aegypti may spread further across Europe, while Aedes albopictus has expanded from eight countries and 114 regions a decade ago to 13 countries and 337 regions in 2026.

Outside Europe, regions such as Los Angeles County in the United States have also reported increased West Nile activity, with at least 100 cases and five deaths recorded this year, illustrating the global nature of the mosquito-borne disease challenge amid changing environmental conditions.