West Nile virus (WNV) transmission is accelerating across Europe as the continent enters the peak period of the mosquito season. By 21 August, 625 locally acquired human cases had been reported in 12 European countries. This represents a substantial increase from the 245 cases reported at the beginning of August.

The increase is not only a matter of case numbers. WNV is also appearing in new areas. Six European regions have reported locally acquired WNV infections for the first time ever in 2026, highlighting the continued geographical expansion of the virus.

Why is August important?

August and early September are typically the peak period for WNV transmission in Europe, as warmer temperatures favour the mosquitoes that transmit the virus.

The current situation also reflects a broader challenge for Europe: mosquito-borne diseases are becoming increasingly important as environmental conditions change and mosquito populations expand.

With the peak transmission period still underway, further cases and newly affected areas can be expected in the coming weeks. The evolution of transmission through late August and September will be key to understanding the overall impact of the 2026 WNV season.