West Nile Virus Spreads in Italy Amid Warming Climate

Italian health authorities are observing a notable expansion in the reach and duration of West Nile virus transmission, attributing the trend to rising temperatures and prolonged warm seasons. This year, Italy has reported over 650 infections, representing approximately half of the cases documented across Europe, according to national health data.

Antonino Bella, a researcher at Italy's National Institute of Health (ISS), explained that elevated temperatures, which are increasingly linked to climate change, accelerate mosquito reproduction and extend the period during which the virus can be transmitted. This heightened activity increases the likelihood of infected mosquitoes spreading the virus to humans.

West Nile virus has been considered endemic in Italy since 2020, with cases consistently appearing during the summer and early autumn months. The majority of infected individuals, around 80%, experience no symptoms. Most others develop a mild, flu-like illness, while severe neurological complications are rare and primarily affect older adults or those with pre-existing health conditions. Current case numbers this year are comparable to recent seasons.

However, Bella noted that warmer weather facilitates mosquito breeding and can extend the transmission season into November. Regions previously less affected are now reporting infections, indicating a gradual geographic expansion of the virus within Italy. The country's experience has drawn international attention, with a Belgian research team visiting the ISS to study Italy's surveillance systems following the emergence of locally acquired West Nile cases in their own country.

Elsewhere in Europe, the Netherlands has recorded more than two dozen West Nile cases this year, along with several fatalities, marking its first cases since 2020. Marc-Alain Widdowson, who leads the World Health Organization's Europe office division for pandemic threats, stated that warming weather undeniably prolongs the virus's and its vector's replication periods in more nations.

"A warming climate means 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 commented, cautioning against attributing the phenomenon solely to climate change while acknowledging its significant role.

Experts suggest that Italy's comprehensive monitoring network, which includes tracking mosquitoes, birds, blood donors, and human infections, contributes to its high detection rates. Widdowson pointed to a warming climate, biodiversity loss, and land-use changes as contributing factors to increased virus activity. A longer mosquito season offers more opportunities for transmission, while a decrease in bird diversity may favor species that are effective reservoirs for the virus.

In June, the European Centre for Disease Prevention and Control (ECDC) issued a warning that Europe's warming trend, characterized by more frequent and severe heat waves, flooding, and longer, warmer summers, creates more favorable conditions for invasive mosquito species like Aedes albopictus and Aedes aegypti. The Aedes aegypti mosquito, capable of transmitting dengue, yellow fever, chikungunya, Zika, and West Nile viruses, is now established in Cyprus and poses a potential risk of spreading to other European countries. The ECDC reported that the Aedes albopictus mosquito has expanded its presence from eight European countries and 114 regions a decade ago to 13 countries and 337 regions currently.