Defining Aedes aegypti density thresholds for preventing human arboviral infections

Effective control of local dengue virus transmission requires reducing the population of mosquitoes below a critical density threshold. Aedes aegypti density thresholds can serve as targets for intervention effectiveness. Most thresholds have been identified by correlating vector densities with pathogen transmission events. However, despite previous descriptive research there is a need for rigorously controlled field studies to clarify the interactions between Ae. aegypti density and human infections. We report on a multi-arm cluster randomized field trial aimed at determining the number of female Ae. aegypti mosquitoes below which dengue outbreaks are limited. We implemented four mosquito control treatments in a dose-response trial, using zero to three Autocidal Gravid Ovitraps (AGO traps) per house across study neighborhoods in Caguas, Puerto Rico from January 2021 to June 2024. We anticipated that significant reductions in Ae. aegypti populations would indicate a threshold density if low or no prevalence of dengue viruses was observed in mosquitoes or antibodies in residents through IgM and IgG serological testing. Results showed that female Ae. aegypti densities decreased by 44 %, 60 %, and 80 % in clusters with one, two, and three traps/house, respectively. The expected number of dengue-infected mosquitoes per thousand were 2.01, 1.70, 0.60, and 0.36 in clusters with zero, one, two, and three traps/house, respectively. Increases in dengue IgG antibody prevalence from 2022 to 2023 were noted only among residents aged 1-10 years, with rates of 25 %, 18 %, 6 %, and 5.9 % corresponding to the number of traps used. To reduce dengue incidence, local populations of Ae. aegypti should be kept below 4 females per AGO trap per week.