Effectiveness of a transfluthrin emanator and insecticide-treated barrier screen in reducing Anopheles biting in a temporary shelter in Sumatra, Indonesia.

Background: The World Health Organization-approved Anopheles interventions target indoor biting and resting behaviour, but are impractical or inapplicable in some settings. In Jambi Province, Sumatra, Indonesia, local indigenous populations sleep under temporary tarpaulin-roofed shelters, complicating the use of bed nets and preventing the application of indoor residual spraying. Two pyrethroid-based interventions were tested alongside a no-intervention control in the field using a Latin-square design. A volatile pyrethroid spatial emanator (SE) offers an easily deployable, simple to use intervention utilizing transfluthrin, while deltamethrin-impregnated barrier screens represents a more permanent intervention.

Methods: Human landing collection was used for mosquito collections throughout the study. Collections occurred near Bukit Duabelas National Park in central Sumatra, Indonesia, an area characterized by secondary forest undergoing widespread conversion to palm and rubber plantations. Collections occurred in three sites located roughly 150 m from each other, with a Latin-square rotational design to account for location and collector effects between experimental replicates. Three complete rotations were achieved over 27 collection nights (a total of 81 trap-nights). Results were analysed with a series of generalized linear models to analyse overall efficacy and the influence of location and device age.

Results: Anopheles host-seeking activity was reduced in the presence of the SE (RR: 0.30 [0.21-0.43], p < 0.001) and barrier screen (RR: 0.39 [0.28-0.54], p < 0.001) interventions compared to control shelters over the course of the study. Similar efficacy was observed among non-Anopheles species. Hourly differences in behaviour were observed, and device age and location were both significant predictors of efficacy in univariate analyses, with efficacy appearing to decrease with device age. However, it was not possible to differentiate between the device age and location effects, since they were correlated due to an error in the rotational design.

Conclusions: Both interventions appeared to reduce Anopheles and non-Anopheles mosquito host-seeking behaviour, highlighting the potential of these forms of outdoor mosquito control. Considerable variation was observed between collection locations, highlighting a difficulty in study design and entomological forecasting. Due to the rotational design where the device age correlated with location, it was difficult to disentangle the relative contributions of these factors. Passive SEs and insecticide-impregnated barrier screens represent interventions that may reduce exposure and hence transmission outdoors.