Abstract
.A cluster-randomized, double-blinded, placebo-controlled trial was conducted to estimate the protective efficacy (PE) of a spatial repellent (SR) against malaria infection in Sumba, Indonesia. Following radical cure in 1,341 children aged ≥ 6 months to ≤ 5 years in 24 clusters, households were given transfluthrin or placebo passive emanators (devices designed to release vaporized chemical). Monthly blood screening and biweekly human-landing mosquito catches were performed during a 10-month baseline (June 2015–March 2016) and a 24-month intervention period (April 2016–April 2018). Screening detected 164 first-time infections and an accumulative total of 459 infections in 667 subjects in placebo-control households, and 134 first-time and 253 accumulative total infections among 665 subjects in active intervention households. The 24-cluster protective effect of 27.7% and 31.3%, for time to first-event and overall (total new) infections, respectively, was not statistically significant. Purportedly, this was due in part to zero to low incidence in some clusters, undermining the ability to detect a protective effect. Subgroup analysis of 19 clusters where at least one infection occurred during baseline showed 33.3% (P-value = 0.083) and 40.9% (P-value = 0.0236, statistically significant at the one-sided 5% significance level) protective effect to first infection and overall infections, respectively. Among 12 moderate- to high-risk clusters, a statistically significant decrease in infection by intervention was detected (60% PE). Primary entomological analysis of impact was inconclusive. Although this study suggests SRs prevent malaria, additional evidence is required to demonstrate the product class provides an operationally feasible and effective means of reducing malaria transmission.
Highlights
It has been nearly 75 years since the role of spatial repellency was first described as a potentially beneficial attribute in malaria control, showing chemicals could effectively disrupt normal host-seeking mosquito behavior and interrupt contact with humans, preventing disease transmission.[1,2,3] Spatial repellency is used here as a general term to refer to a range of insect behaviors induced by airborne, volatile chemicals that result in a reduction in human–vector contact
The primary objective of this large-scale RCT conducted on Sumba Island, Indonesia, was to demonstrate and quantify the protective efficacy (PE) of a passive emanating spatial repellent (SR) intervention, for reducing malaria incidence in humans
Sumba Island, Indonesia, represents a group of malaria-endemic settings where SRs are intended to be implemented if/when a policy recommendation is endorsed as Sumba does not currently conduct routine IRS, long-lasting insecticidal nets (LLINs) were only recently distributed, and there is a range of anopheline biting habits by local vectors, including early-evening and/or outdoor biting
Summary
It has been nearly 75 years since the role of spatial repellency (deterrence or avoidance) was first described as a potentially beneficial attribute in malaria control, showing chemicals could effectively disrupt normal host-seeking mosquito behavior and interrupt contact with humans, preventing disease transmission.[1,2,3] Spatial repellency is used here as a general term to refer to a range of insect behaviors induced by airborne, volatile chemicals that result in a reduction in human–vector contact. Most commercial spatial repellent (SR) products use either low concentrations of short-duration United States Environmental Protection Agency (USEPA) registered synthetic pyrethroids (pyrethrin, metofluthrin, and more recently transfluthrin)[13] or botanical-based compounds.[14,15]
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