West Nile Virus Spreading to New Regions as Warmer Climates Expand Mosquito Range

West Nile virus, transmitted primarily by Culex mosquitoes, is being detected in geographic areas of Europe and North America where it was either absent or very rare a decade ago. Public health authorities in several European countries and multiple US states have issued alerts this summer as case counts climb above recent historical norms.

Shifting Geographic Range

The expansion is being driven primarily by rising temperatures and changes in rainfall patterns consistent with climate change. Culex mosquitoes, which carry the virus from infected birds to humans, thrive in warm, stagnant water environments. As average temperatures rise across central and northern Europe and parts of Canada, habitat suitable for these mosquitoes has extended northward and to higher altitudes.

Current Outbreak Situation

Italy, Greece, and parts of France and Germany have reported elevated case numbers this season. In the United States, states in the upper Midwest and Pacific Northwest — historically less affected — have recorded an uptick in infections. Most West Nile infections cause no symptoms or mild flu-like illness, but roughly one in 150 cases develops into serious neurological disease, including encephalitis and meningitis, which can be fatal.

Public Health Response

Authorities have intensified mosquito surveillance and control programmes, including aerial larvicide spraying near standing water and increased testing of dead birds, which serve as an early indicator of virus circulation. Residents in affected areas have been advised to use insect repellent, wear long sleeves at dawn and dusk when mosquito activity peaks, and eliminate standing water around homes.

Climate Link

Epidemiologists studying vector-borne diseases say West Nile is among several pathogens whose geographic range is expanding as a direct consequence of climate change. Dengue, chikungunya, and Usutu virus — the latter causing bird die-offs and occasionally human infections in Europe — show similar northward shifts. Experts warn that existing public health infrastructure in newly affected areas may be unprepared for sustained seasonal transmission.