Indoor spray and windows screens effects on dengue vector density after space spraying in a field trial

Objective: To demonstrate the effect of indoor spraying and window screens on Aedes aegypti mosquito density after space spraying. Methods: A total of 141 households (the study houses) in six communities of Songkhla City, located in Songkhla Province of southern Thailand, were randomly selected and the adult Ae. aegypti populations were assessed pre- and post-insecticide spraying from March to October, 2014. Houses close to (within a 20 m radius) the study houses were analyzed using spatial analysis tools. The Aedes aegypti density in the study houses and house density index were compared with the density in the neighbouring houses, based on three spraying conditions: (i) unsprayed (ii) only outdoor sprayed and (iii) indoor plus outdoor sprayed. Results: Only spraying houses indoors was the most effective (P<0.05). There was insufficient evidence that the source of the increase in the number of mosquitoes in unsprayed houses was due to their migration from neighbouring houses which had been sprayed. However, the study houses without screens on their windows were found to have a likely higher dengue vector population after spraying, but the difference was not significant. Conclusions: In dengue endemic areas, all houses should be fully screened and the number of houses ultra-low volume sprayed indoor plus outdoor should be increased with the cooperation of householders and communities during epidemics.