Invasive mosquito surveillance in the United Kingdom 2020 to 2024: First detection of Aedes aegypti eggs in the UK and further detection of Aedes albopictus.

Here, we provide an update on invasive mosquito surveillance activities coordinated by the UK Health Security Agency (UKHSA) between May 2020 and November 2024. Aedes albopictus and Aedes aegypti are invasive mosquitoes and not currently established in the UK. Both are vectors of various arboviruses including emerging pathogens such as dengue. Therefore, their introduction into the UK poses a threat to public health. In 2024, vector surveillance to detect and limit the establishment of invasive mosquito species involved 1070 ovitraps at 117 localities across England, Wales and Northern Ireland, expanding from 58 in 2019. Ovitraps at seaports, airports, and highway transport hubs were examined every two weeks, between May and October, each year. In 2020, 2021 and 2022, no Ae. albopictus specimens were detected. In September 2023, Aedes aegypti eggs were detected in a freight storage facility near Heathrow Airport. Identification of these eggs was confirmed morphologically and molecularly. Targeted enhanced surveillance yielded no further detections, suggesting an isolated incursion. In August 2024, Ae. albopictus was detected for the first time since 2019. Four eggs were found in an ovitrap at a service station along the M20 motorway in Kent, in South East England. In accordance with existing national contingency planning, the local authority collaborated with the landowner and UKHSA to conduct larval source reduction, and UKHSA conducted enhanced surveillance. There were no further detections of eggs or adult Ae. albopictus mosquitoes during the enhanced surveillance period. This project is complemented by UKHSA's broader mosquito surveillance efforts, including deploying adult mosquito traps in 307 localities across England and Wales, and a mosquito recording scheme that accepts submissions from the public. Combined, our findings suggest that future incursions of invasive mosquitoes in the UK are likely and undertaking enhanced surveillance is key to identifying and reducing the likelihood of their establishment.