The impact of treated eave ribbons in reducing malaria transmission; A mathematical modelling perspective

Abstract Background Despite significant progress against malaria, the use of two core interventions, namely insecticide-treated nets (ITNs) and indoor residual spraying (IRS), are becoming increasingly vulnerable due to insecticide resistance and outdoor biting by mosquitoes. One representative example is Kilombero Valley in Tanzania where transmission continues despite over 80% of the population using ITNs. Further progress in this and similar African settings will require identifying which supplementary tools combine most effectively with ITNs to reduce mosquito exposure. Methods Using the Kilombero Valley as a case study, the Vector Control Optimization Model (VCOM) was adapted and extended to simulate the impact of adding eave ribbons treated with spatial repellent (ER) as supplementary intervention in an area of high ITN coverage. Simulation was conducted to assess the impact of varying coverage of this supplementary intervention on the entomological inoculation rates (EIR) generated by two common vectors in Kilombero, Anopheles arabiensis and Anopheles funestus . Finally, the impact of introducing this intervention on the combined EIR from An. arabiensis and An. funestus was assessed to identify scenarios in which values fell below 1; the likely threshold required for malaria interruption. Results ER was predicted to substantially reduce the EIR in Kilombero valley when combined with 80% ITN coverage. However, the nature of the impact varied notably between vector species. ER was predicted to have a much larger effect on transmission mediated by An. funestus than An. arabiensis . Additionally, in the situation where EIR from both An. arabiensis and An. funestus was combined, substantial coverage of this supplementary intervention was predicted to lower EIR to below one. Conclusion Despite the significant impact of ER in combination with ITNs on one of the two vectors ( An. funestus or An. arabiensis ), this intervention is insufficient when combined with ITNs to reduce the EIR to below one in settings like Kilombero Valley where both species contribute to malaria transmission.