Monitoring of mosquito breeding sites in the municipality of Cascais, Portugal

Abstract Culex pipiens is the primary West Nile Virus vector in Portugal. Additionally, in 2017, Aedes albopictus, vector of various arboviruses, was detected in Northern Portugal. To mitigate viral transmission risks, effective surveillance is crucial, including monitoring egg, larva, and pupa stages. Located on the west of Lisbon, Cascais implemented a surveillance based on monitoring invasive species at Points of Entry and, complementarily, on detecting and intervening in breeding sites. Active searches for new breeding sites and monitoring those that were already identified are conducted weekly during the peak mosquito season (May to October) and biweekly during the colder season (November to April), following the methodology outlined below: • Upon detection, samples of immature stages are collected for submission to the National Institute of Health (INSA); • Corrective measures are requested to the managing entities of the locations where the sites are found; • Date of action, location, collection point, date of report, and status (pending or intervened) are recorded on a database; • Locations with pending status undergo continuous monitoring. In 2023, 16 artificial breeding sites were identified. These findings resulted from 23 actions conducted across 8 locations. 35 samples of immatures were collected, followed by their submission and notification to the respective managing entities. Recurrent detections were noted in 9 breeding sites. The managing entities implemented measures at 13 of the identified sites, leaving 3 with pending intervention. The identification of breeding sites demands continuous monitoring efforts and requires an effective coordination between the Public Health services and the management entities. Based on the achieved outcomes, it is evident that the implementation of corrective measures has been successful, making a significant contribution to reducing mosquito density. Key messages • Effective surveillance and intervention strategies are crucial in mitigating West Nile Virus and arbovirus transmission risks in Portugal. • Continuous monitoring and coordination between public health services and management entities are key for maintaining effective vector control measures.