Abstract
BackgroundLong-lasting insecticidal nets (LLINs) are a key malaria control intervention, but their effectiveness is threatened by resistance to pyrethroid insecticides. Some new LLINs combine pyrethroids with piperonyl butoxide (PBO), a synergist that can overcome P450-based metabolic resistance to pyrethroids in mosquitoes. In 2017–2018, the Ugandan Ministry of Health distributed LLINs with and without PBO through a national mass-distribution campaign, providing a unique opportunity to rigorously evaluate PBO LLINs across different epidemiological settings.Methods/designTogether with the Ministry of Health, we embedded a cluster-randomised trial to evaluate the impact of LLINs delivered in the 2017–2018 national campaign. A total of 104 clusters (health sub-districts) in Eastern and Western Uganda were involved, covering 48 of 121 (40%) districts. Using adaptive randomisation driven by the number of LLINs available, clusters were assigned to receive one of four types of LLINs, including two brands with PBO: 1) PermaNet 3.0 (n = 32) and 2) Olyset Plus (n = 20); and two without PBO: 3) PermaNet 2.0 (n = 37) and 4) Olyset Net (n = 15). We are conducting cross-sectional community surveys in 50 randomly selected households per cluster (5200 households per survey) and entomological surveillance for insecticide resistance in up to 10 randomly selected households enrolled in the community surveys per cluster (1040 households per survey) at baseline and 6, 12, and 18 months after LLIN distribution. Net durability and bio-efficacy will be assessed in 400 nets withdrawn from households with replacement at 12 months. The primary trial outcome is parasite prevalence as measured by microscopy in children aged 2–10 years in the follow-up surveys.DiscussionPBO LLINs are a promising new tool to reduce the impact of pyrethroid resistance on malaria control. The World Health Organization has issued a preliminary endorsement of PBO LLINs, but additional epidemiological evidence of the effect of PBO LLINs is urgently needed. The results of this innovative, large-scale trial embedded within a routine national distribution campaign will make an important contribution to the malaria control policy in Uganda and throughout Africa, where pyrethroid resistance in malaria vectors has increased dramatically. This model of evaluation could be a paradigm for future assessment of malaria control interventions.Trial registrationISRCTN, ISRCTN17516395. Registered on 14 February 2017.World Health Organization Trial Registration Data SetSee Additional file 1.
Highlights
Long-lasting insecticidal nets (LLINs) are a key malaria control intervention, but their effectiveness is threatened by resistance to pyrethroid insecticides
piperonyl butoxide (PBO) LLINs are a promising new tool to reduce the impact of pyrethroid resistance on malaria control
The World Health Organization has issued a preliminary endorsement of PBO LLINs, but additional epidemiological evidence of the effect of PBO LLINs is urgently needed
Summary
Long-lasting insecticidal nets (LLINs) are a key malaria control intervention, but their effectiveness is threatened by resistance to pyrethroid insecticides. In Uganda, progress on reducing malaria transmission has been slow, despite the scale-up of long-lasting insecticidal nets (LLINs), indoor residual spraying (IRS), and treatment of symptomatic malaria cases with artemisinin-based combination therapies, and control gains have been difficult to sustain [3,4,5,6]. Completed trials suggest that, even in areas of increased insecticide resistance, users of LLINs have lower prevalence and incidence of malaria than non-users, these studies have not quantified the extent to which the community or mass effect may have been lost [14, 15]
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