Italy sees mosquitoes spread West Nile virus farther and longer as Europe warms

Mosquitoes in Italy are spreading West Nile virus to more people, in more places, and during more months of the year. Italian health officials say warmer temperatures caused by climate change are a big reason why. So far this year, Italy has reported more than 650 cases of the virus — about half of all cases recorded across Europe. Scientists are watching this trend closely because it could affect many other countries too.

West Nile virus has been common in Italy every summer since around 2020. Most people who get infected — about 80 percent — never feel sick at all. Others might feel like they have a mild flu. A small number of people, mostly older adults or those with serious health problems, can develop dangerous brain-related illnesses. Experts say this year's numbers are similar to recent years, but the pattern of the disease spreading wider and later in the year is a growing concern.

Warmer weather helps mosquitoes reproduce faster and stay active longer into the fall. Antonino Bella, a researcher at Italy's National Institute of Health, said that higher temperatures linked to climate change give mosquitoes more time to bite people and spread the virus. In some years, the transmission season has stretched all the way into November. Areas of Italy that rarely dealt with West Nile before are now seeing cases every year.

Other European countries are paying close attention to what is happening in Italy. A research team from Belgium visited Italy in May to learn how Italian scientists track and study the virus. The Netherlands reported more than two dozen West Nile cases this year, along with several deaths — its first cases since 2020. Italy's strong monitoring system, which watches mosquitoes, birds, blood donors, and human infections, helps it catch more cases than countries without such networks.

The World Health Organization's Europe office is also watching the situation. Marc-Alain Widdowson, a top official there, said warmer weather will allow the virus and the mosquitoes that carry it to spread to more countries over time. He noted that climate change is not the only reason for the rise in cases, but it is a major factor. Changes in land use and a loss of different animal species also play a role.

European health officials have warned that certain invasive mosquito species are spreading because of warming temperatures. One species, called Aedes albopictus, was found in 8 European countries and 114 regions just ten years ago. Today, it is established in 13 countries and 337 regions. Another species, Aedes aegypti, has already settled in Cyprus and could move into more European countries as temperatures keep rising.

West Nile virus is not only a problem in Europe. In Los Angeles County, health officials reported at least 100 cases and five deaths linked to mosquitoes this year. Experts around the world agree that longer, hotter summers create better conditions for mosquitoes to thrive and spread diseases. Understanding how climate change drives these patterns is becoming an important part of public health planning everywhere.