Addressing The West Nile Virus Health Crisis: Surveillance And Integrated Vector Management In Spain

We conducted a comprehensive study to target both adult and immature stages across six municipalities (around 270.00 inhabitants) in southern Spain, where ca. 1/3 of all Spanish WNV cases were reported. A total of 729 sampling sites were identified and regularly visited over four months, involving a total sampling effort of 4,026 visits. Adult mosquitoes were monitored using suction traps, while immature stages were sampled using dipping techniques. Eleven mosquito species were identified, with high abundance of two primary urban WNV vectors: Culex perexiguus and Culex pipiens. The former was the most abundant based on adult collection (47.1%) and the latter by examination of larvae (90.8%). These mosquitoes were found breeding in 136 sites (18.6% of the total sites) with diverse waterlogged habitats, particularly rice fields, ditches, and canals near urban zones. A total of 190 blood-fed Culex mosquitoes were collected and analyzed to determine their host-feeding preferences. Our multi-strategy control approach targeted immature mosquitoes using Bacillus thuringiensis var. israelensis (Bti) and adult mosquitoes using cypermethrin-based adulticides at 138 positive points resulting in 266 control interventions. We assessed the effectiveness of the control measures by comparing the number of larvae before and after larviciding, and we found that Bti successfully eliminated and/or reduced immature stages in 80% of the treated sites; however, mosquito populations quickly rebounded if the interventions were not maintained constantly.