Estimating the impact of transfluthrin-treated eave ribbons, Suna traps and their combination on malaria case incidence, based on semi-field and field data

Global malaria incidence has been reduced drastically since the year 2000, primarily due to the widespread use of insecticide-treated nets (ITNs), which kill the bloodfeeding Anopheles mosquitoes vectoring the disease in addition to protecting individuals sleeping under them from bites. However, progress has stalled since the mid-2010s and malaria continues to kill more than half a million people globally each year. New, complementary vector control tools are needed to further reduce the residual malaria transmission and face a potential decline in ITN effectiveness due to insecticide resistance. Transfluthrin-treated eave ribbons are a promising spatial repellent to protect people when they are in or around the house but not under an ITN, while the odour-baited Suna trap may present an insecticide-free means of killing mosquitoes. In previous semi-field and field studies, we assessed the effect of the eave ribbon, the Suna trap and the combined push-pull system on mosquito-human contact and mosquito mortality. Here, we combine this evidence and predict the malaria case incidence reduction if these interventions were deployed at a large scale in two East African transmission settings under full uncertainty quantification by use of a stochastic, individual-based simulation platform of malaria epidemiology. Our simulations suggest that the transfluthrin-treated eave ribbon may substantially reduce malaria case incidence in settings with low-transmission or with low ITN use, especially in regions where Anopheles funestus dominates among malaria vectors and primarily uses human hosts. However, by diverting mosquitoes from indoor to outdoor host-search, the eave ribbon may reduce the community-protective killing effect of ITNs. In addition, people neither protected by an ITN nor the eave ribbon may experience an increase in malaria incidence at high but imperfect coverage with the eave ribbon. The Suna trap only showed a marginal effect on case incidence and the effect of the combined push-pull system was similar to the effect of the eave ribbon alone. Hence, the eave ribbon appears to be a promising tool in settings difficult to reach with ITNs, such as migrant agricultural workers, but deployment alongside ITNs needs to be planned with care, and ensuring the highest possible use of ITNs remains crucial.