By 30 September 16 European countries had reported 1,765 locally acquired cases of West Nile virus, a mosquito-borne infection carried by wild birds, according to ECDC, the EU's disease-control agency1. On 3 September the count stood at 1,086 against a ten-year average of 736 for that date, which put the season nearly 48% above the decade's norm2. The Netherlands recorded its first human cases since 2020, one of them fatal, and Greece its highest count for the time of year, 284 cases and 24 deaths by 3 September.
A locally acquired case means a mosquito in Europe bit an infected host and then a person, so the whole cycle ran on the continent rather than on a trip abroad. France has 124 locally acquired cases of Chikungunya, a mosquito-borne virus that causes fever and long-lasting joint pain, in 19 clusters, 34 of them added in the last week of September3. Italy has 59 local cases of Dengue, a mosquito-borne fever that can turn severe. France also carries local mosquito-borne transmission beyond the mainland: in Mayotte, its Indian Ocean department, ECDC counted 63 locally acquired malaria cases by late May.
In east London, the UK Health Security Agency (UKHSA) found a breeding population of Aedes aegypti, the main carrier of Dengue, Chikungunya, Zika and yellow fever, in August4. A member of the public reported it through UKHSA's Mosquito Watch scheme. The agency is treating the site with larvicide, insecticide that kills mosquito larvae in standing water, and aims to eradicate it. ECDC says it is unclear whether the species could establish in the current UK climate.
