Lessons learned, challenges and outlooks for decision-making after a decade of experience monitoring the impact of indoor residual spraying in Benin, West Africa

Abstract

Background: Since 2008, Indoor Residual Spraying (IRS) has been performed in Benin in 19 districts, including 4 in southern Benin, 9 in Atacora, and 8 in Atacora, Alibori and Donga in northern Benin. However, Benin still struggles with questions about IRS cost-benefit and epidemiological impact. Lessons learned and challenges from 10 years of IRS in Benin to be shared with the stakeholders involved in vector control implementation for decision-making. Methods: Entomological parameters have been assessed entomological parameters in IRS communes since 2008. In all IRS intervention communes, decreases in human biting rate (HBR) of Anopheles gambiae, blood feeding inhibition and entomological inoculation rate (EIR) as compared to control district have been measured. Results: EIR was reduced by 80-90%, which is encouraging, but should be observed with caution because: (i) the reduction may be insufficient to decrease epidemiological indicators given that the residual EIR in IRS districts is still higher than it is in some regions of stable malaria; (ii) the reduction in EIR is based on comparisons with control communes, but it is difficult to select control areas with the same environmental characteristics as intervention areas; (iii) despite the reduction, half of all mosquitoes that entered IRS-treated houses succeeded in taking human blood meals. Further, there are behaviours among Benin's population that limit IRS efficacy, including recent data showing that > 90% of people are not protected by IRS between 7 and 10 p.m. This is due to the fact that they remain outdoors and that most people are not protected from mosquito bites after 10 p.m. because they either sleep outdoors without IRS protection or indoors without an ITN. Moreover, people have large amounts of clothing hanging on walls where mosquitoes can rest instead of IRS-treated walls. Finally, other components are important to consider in implementing IRS among which: (i) Vector resistance management strategies are sometimes poorly understood; this is actually different from the need to replace one insecticide with another after the emergence of resistance; (ii) African countries should prepare to finance IRS themselves. Conclusion: To curtail residual malaria transmission, additional interventions able to target vectors escaping IRS should be prioritized.

Malaria Burden and Associated Risk Factors in an Area of Pyrethroid-Resistant Vectors in Southern Benin

“…3 In Benin, malaria remains a serious public health issue despite the scale-up of LLINs, indoor residual spraying, and malaria case management. 4 , 5 According to the national health statistics, 2,719,608 malaria cases were recorded in 2019 representing 45.5% of the overall outpatient diagnoses with 3,509 deaths attributable to malaria. 6 In 2018, more than 90% of households declared to have at least one insecticide-treated net, and 71% had slept under nets the night before the survey.…”

VECTRON™ T500, a new broflanilide insecticide for indoor residual spraying, provides prolonged control of pyrethroid-resistant malaria vectors

“…This reduction in both biting rate and survival of vectors, considerably lowers indoor malaria transmission risk. Despite the undoubted effectiveness of IRS demonstrated in many transmission settings [ 4 – 7 ], the high prevalence of resistance in Anopheles vectors to the limited number of classes of insecticides available for this intervention [ 8 ], is of serious concern. Pyrethroid resistance is now widespread and increasing in intensity in major malaria vectors across Africa while resistance to the three other insecticide classes commonly used in IRS up to 2016 (organophosphates, carbamates and DDT), has been confirmed across malaria endemic countries in the five World Health Organization (WHO) regions [ 8 ].…”

Six decades of malaria vector control in southern Africa: a review of the entomological evidence-base

“…For sustainability of the currently implemented strategies (IRS and LLINs), there is a need to assess the cost-effectiveness as well as the timely deployment. One of the setbacks in IRS implementation in the SAR is logistics involving delays in shipments thus receiving insecticides when the spraying season is over or when the insecticides have expired [ 195 , 212 ]. The financial and technical cost needs a thorough assessment to drive malaria transmission down to zero while these approaches should be judiciously considered and supported by both government and donors to achieve the goal of malaria elimination.…”