Implementation of a cluster randomized trial to reveal Aedes aegypti's (Diptera: Culicidae) density threshold for dengue virus transmission in Puerto Rico

The main objective is establishing the minimum numbers of Aedes aegypti mosquitoes required to prevent rampant outbreaks of arboviruses such as dengue (threshold density). Mass trapping with three Autocidal Gravid Traps (AGO traps) per home in most homes within neighborhoods reduced Ae. aegypti densities below levels that protected people against outbreaks of novel arboviruses such as chikungunya. In this investigation we intend to cause steady, decreasing levels of Ae. aegypti densities by increasing the number of AGO traps per home for three years (2021-2024) of observations in Puerto Rico. The experimental design included randomly selecting 12 replicate clusters (300 houses each) with similar historical densities of Ae. aegypti, and applying the following treatments: 0, 1, 2, or 3 traps per house. Mosquito abundance is monitored weekly and collected females of Ae. aegypti are pooled and analyzed for RNA of dengue, chikungunya, and Zika viruses. Human infections will be monitored using annual serosurveys. Preliminary results showed the establishment of four separate, decreasing levels of Ae. aegypti in clusters with increased number of traps/house. There were 53, 68, and 82% reductions in average females of Ae. aegypti/trap/week in clusters with 1, 2, or 3 traps per house in comparison with non-treated clusters. These preliminary results indicate that it is possible to establish varying levels of mosquito densities in nature that could be related to local arbovirus transmission.