Combining next-generation indoor residual spraying and drug-based malaria control strategies: observational evidence of a combined effect in Mali

Abstract

Background: Ségou Region in central Mali is an area of high malaria burden with seasonal transmission. The region reports high access to and use of long-lasting insecticidal nets (LLINs), though the principal vector, Anopheles gambiae, is resistant to pyrethroids. From 2011 until 2016, several high-burden districts of Ségou also received indoor residual spraying (IRS), though in 2014 concerns about pyrethroid resistance prompted a shift in IRS products to a micro-encapsulated formulation of the organophosphate insecticide pirimiphos-methyl. Also in 2014, the region expanded a pilot programme to provide seasonal malaria chemoprevention (SMC) to children aged 3-59 months in two districts. The timing of these decisions presented an opportunity to estimate the impact of both interventions, deployed individually and in combination, using quality-assured passive surveillance data. Methods: A non-randomized, quasi-experimental time series approach was used to analyse monthly trends in malaria case incidence at the district level. Districts were stratified by intervention status: an SMC district, an IRS district, an IRS + SMC district, and control districts that received neither IRS nor SMC in 2014. The numbers of positive rapid diagnostic test (RDT +) results reported at community health facilities were aggregated and epidemiological curves showing the incidence of RDT-confirmed malaria cases per 10,000 person-months were plotted for the total all-ages and for the under 5 year old (u5) population. The cumulative incidence of RDT + malaria cases observed from September 2014 to February 2015 was calculated in each intervention district and compared to the cumulative incidence reported from the same period in the control districts. Results: Cumulative peak-transmission all-ages incidence was lower in each of the intervention districts compared to the control districts: 16% lower in the SMC district; 28% lower in the IRS district; and 39% lower in the IRS + SMC district. The same trends were observed in the u5 population: incidence was 15% lower with SMC, 48% lower with IRS, and 53% lower with IRS + SMC. The SMC-only intervention had a more moderate effect on incidence reduction initially, which increased over time. The IRS-only intervention had a rapid, comparatively large impact initially that waned over time. The impact of the combined interventions was both rapid and longer lasting.

Pirikool® 300 CS, a new long-lasting capsule suspension formulation of the organophosphate insecticide pirimiphos-methyl for indoor residual spraying against pyrethroid-resistant malaria vectors

“…A new microencapsulated formulation of pirimiphos-methyl (Actellic® 300CS) which demonstrated vastly improved residual duration up to 12 months after application in experimental hut trials in Benin and Tanzania [ 8 , 9 ] was eventually recommended by WHO [ 10 ]. Largescale application of this formulation for IRS in sub-Saharan Africa [ 5 ] provided substantial control of mosquito vectors and malaria in many settings [ 11 – 18 ].…”

Stratification At The Health District Level And Targeting of Malaria Control Interventions In Mali

“…They carry out clinical, parasitological, and entomological surveillance. Resistance to insecticides [51][52][53] has been observed in the majority of A. gambiae vectors, with the exception of two which are pyrimiphos-methyl in Koulikoro [44] and Clothianidins (Neoticotinoid) [54]. This resistance appears to be widespread in Mali and could compromise the effectiveness of vector control.…”

Stratification at the Health District Level for Targeting Malaria Control Interventions in Mali

“…They carry out clinical, parasitological, and entomological surveillance. Resistance to insecticides has been observed in the majority of A. gambiae vectors, with the exception of two which are pyrimiphos-methyl in Koulikoro 35,36 and Clothianidins (Neoticotinoid) 37 . This resistance appears to be widespread in Mali and could compromise the effectiveness of vector control.…”

“…The prevention strategies, IPT, IRS and SMC should be continued, and the extension of SMC to children aged from 5 to years is being considered. IG2-LLIN distributions should be developed, due to the spread of insecticide resistance [57][58][59] .…”