Aargau
Swiss canton in the north of the country.
Aargau, a canton on Switzerland's northern border with Germany, is where the country's first locally acquired West Nile virus infection was found: a horse in Kaisten, reported on 26 August 2026.
Last refreshed: 4 October 2026
Timeline for Aargau
Mentioned in: Europe's West Nile cases reach 1,765
Pandemics and BiosecurityBackground
Aargau recorded Switzerland's first locally acquired West Nile virus infection in 2026. The Institute of Virology and Immunology reported on 26 August that a horse on a farm in Kaisten, which had never been abroad, had the virus. The horse recovered.
The case came in a European season running well above average. On 3 September the count of locally acquired human infections stood at 1,086 against a ten-year average of 736, and by 30 September 16 European countries had reported 1,765, ECDC said. Mosquito-borne viruses reached further north that year, and the Netherlands had its first human West Nile cases since 2020.
Aargau is a canton in northern Switzerland. Kaisten lies on the Rhine, on the border with Germany.