Combining Organophosphate Treated Wall Linings and Long-lasting Insecticidal Nets for Improved Control of Pyrethroid Resistant Anopheles gambiae

Abstract

BackgroundNew approaches to delivering insecticides need to be developed to improve malaria vector control. Insecticidal durable wall lining (DL) and net wall hangings (NWH) are novel alternatives to indoor residual spraying which can be produced in a long-lasting format. Non-pyrethroid versions could be used in combination with long-lasting insecticidal nets for improved control and management of insecticide resistant vector populations.MethodsExperimental hut trials were carried out in Valley du Kou, Burkina Faso to evaluate the efficacy of pirimiphos methyl treated DL and NWH either alone or in combination with LLINs against pyrethroid resistant Anopheles gambiae ss. Comparison was made with pyrethroid DL. Mosquitoes were genotyped for kdr and ace-1R resistant genes to investigate the insecticide resistance management potential of the combination.ResultsThe overall kdr and ace-1R allele frequencies were 0.95 and 0.01 respectively. Mortality with p-methyl DL and NWH alone was higher than with pyrethroid DL alone (>95% vs 40%; P<0.001). Combining pyrethroid DL with LLINs did not show improvement in mortality (48%) compared to the LLIN alone (44%) (P>0.1). Combining p-methyl DL or NWH with LLINs reduced biting rates significantly (8–9%) compared to p-methyl DL and NWH alone (>40%) and killed all An gambiae that entered the huts. Mosquitoes bearing the ace-1R gene were more likely to survive in huts with p-methyl DL alone (p<0.03) whereas all resistant and susceptible genotypes were killed by the combination.ConclusionP-methyl DL and NWH outperformed pyrethroid DL. Combining p-methyl DL and NWH with LLINs could provide significant epidemiological benefits against a vector population which is resistant to pyrethroids but susceptible to organophosphates. There was evidence that the single intervention would select kdr and ace-1R resistance genes and the combination intervention might select less strongly. Technology to bind organophosphates to plastic wall lining would be worth developing.

Chlorfenapyr (A Pyrrole Insecticide) Applied Alone or as a Mixture with Alpha-Cypermethrin for Indoor Residual Spraying against Pyrethroid Resistant Anopheles gambiae sl: An Experimental Hut Study in Cove, Benin

“…While chlorfenapyr IRS was clearly superior to alpha-cypermethrin IRS against the Cove vector population, the mortality rate achieved was (63%) less than what has been reported with some currently used non-pyrethroid IRS insecticides (>75% mortality) [14, 15]. Similar mortality rates have been achieved with chlorfenapyr IRS at much higher application rates (500mg/m 2 ) [7] showing that the maximum impact of the insecticide for IRS will not require doses higher than 250mg/m 2 as used in the current study.…”

Trends in the selection of insecticide resistance in Anopheles gambiae s.l. mosquitoes in northwest Tanzania during a community randomized trial of longlasting insecticidal nets and indoor residual spraying

“…Elsewhere in West Africa, new alternative insecticides such as chlorfenapyr are being tested for the control of pyrethroid‐resistant mosquitoes in experimental huts (N'Guessan et al ., ; Ngufor et al ., ). Experimental hut studies provide some empirical data in support of interventions which combine the use of LLINs and IRS and indicate that these constitute a potential tool for the management of vector resistance (Djènontin et al ., ; Ngufor et al ., , ), but data on the differential survival of alleles or resistance and susceptibility in these small‐scale hut studies are too limited to be conclusive.…”

Insecticide-treated durable wall lining (ITWL): future prospects for control of malaria and other vector-borne diseases

“…gambiae s.s. r Significantly higher mortality with p -methyl WL than pyrethroid WL (66% vs. 32%, respectively)Significant reductions in mosquito entry for p-methyl WL/NHW only when combined with LLIN (59%/65% vs. 28%/3%, respectively)Significantly increased exiting rates for p-methyl WL (53%) and p-methyl NWH + LLIN (59%), relative to untreated control (29%)Limited effect on blood feeding rates (82–94%) relative to untreated control (95%), unless combined with LLIN (9–13%)Limited personal protection for p-methyl WL/NWH relative to untreated control (4%/0%), unless combined with LLIN (93%/92%)Significantly higher numbers of ace - 1 R heterozygote ( RS ) and homozygote ( RR ) survivors compared to susceptible homozygotes ( SS ) following exposure to p-methyl WLs/NHWs[47]Four walls + ceilingHoled untreated mosquito netNo improvement in mosquito mortality when p-methyl WL/NWH coverage increased from walls only (66%/49%) to walls + ceilings (56%/69%)Combined WL and LLIN did not limit the selection of ace - 1 R compared to WL aloneNylon NHWPirimiphos methyl (1 g/m 2 )Four wallsFour walls + ceilingUntreated plastic sheetingNo increase in mosquito mortality when WL/NHW combined with LLINs (72%/61% vs. 61%/53%, respectively)Polyethylene WL (ZeroVector ® )Deltamethrin (175 mg/m 2 )Four wallsBobo Dioulasso, Burkina Faso, experimental West African hutsPolyethylene WLPirimiphos methyl (1 g/m 2 )Four wallsHoled deltamethrin LLIN (PermaNet ® 2.0; 55 mg/m 2 ) An. gambiae s.s. s/r (c) Significantly higher mortality with p-methyl WL than pyrethroid WL (>95% vs. 40%, respectively)Largest reductions in mosquito entry for pyrethroid WL and p-methyl WL when used in combination with LLIN (74 and 62%, respectively)Significantly increased exiting rates for p-methyl WL (53%), relative to untreated control (33%)Blood feeding significantly reduced when p-methyl WL/NWHs combined with LLIN (91%/90% vs. 50/50%, respectively) Personal protection for p-methyl WL/NWH relative to untreated control (56%/72%), increased when combined with LLIN (95%/94%)Significantly higher numbers of ace - 1 R survivors (100%) following exposure to p-methyl WL alone, compared to susceptible vectors (32%)[48]Four walls + ceiling…”