Entomological outcomes of cluster-randomised, community-driven dengue vector-suppression interventions in Kampong Cham province, Cambodia

Abstract

Cambodia has one of the highest dengue infection rates in Southeast Asia. Here we report quantitative entomological results of a large-scale cluster-randomised trial assessing the impact on vector populations of a package of vector control interventions including larvivorous guppy fish in household water containers, mosquito trapping with gravid-ovitraps, solid waste management, breeding-container coverage through community education and engagement for behavioural change, particularly through the participation of school children. These activities resulted in major reductions in Container Index, House Index, Breteau Index, Pupal Index and Adult Index (all p-values 0.002 or lower) in the Intervention Arm compared with the Control Arm in a series of household surveys conducted over a follow-up period of more than one year, although the project was not able to measure the longer-term sustainability of the interventions. Despite comparative reductions in Adult Index between the study arms, the Adult Index was higher in the Intervention Arm in the final household survey than in the first household survey. This package of biophysical and community engagement interventions was highly effective in reducing entomological indices for dengue compared with the control group, but caution is required in extrapolating the reduction in household Adult Index to a reduction in the overall population of adult Aedes mosquitoes, and in interpreting the relationship between a reduction in entomological indices and a reduction in the number of dengue cases. The package of interventions should be trialled in other locations. Author summary Dengue is a virus transmitted by mosquitoes which causes unpleasant flu-like symptoms and has no specific treatment. In Cambodia, mosquitoes which can carry dengue virus breed in fresh water collected in containers such as the large clay jars used for domestic water storage in the many rural parts of the country which lack piped household water supply. This study examined a package of interventions including putting mosquito larvae-eating guppy fish in household water containers, trapping adult mosquitoes, removing mosquito breeding sites from around houses and providing community education about dengue, particularly to school children. The study found that implementing this package of interventions significantly reduced the number of household water containers which contained mosquito immature stages, the average number of mosquito pupae per house and the average number of adult mosquitoes per house when compared with a control group which did not implement the package. Though these results are promising, it is not certain that these reductions will directly translate to a reduction in the number of people in the study areas becoming infected with dengue and more studies are needed to investigate this link.