Combining organophosphate-treated wall linings and long-lasting insecticidal nets fails to provide additional control over long-lasting insecticidal nets alone against multiple insecticide-resistant Anopheles gambiae in Côte d’Ivoire: an experimental hut trial

Abstract

BackgroundInsecticide-treated wall lining (ITWL) is a new concept in malaria vector control. Some Anopheles gambiae populations in West Africa have developed resistance to all the main classes of insecticides. It needs to be demonstrated whether vector control can be improved or resistance managed when non-pyrethroid ITWL is used alone or together with long-lasting insecticidal nets (LLINs) against multiple insecticide-resistant vector populations.MethodsTwo experimental hut trials were carried out as proofs of concept to evaluate pirimiphos methyl (p-methyl)-treated plastic wall lining (WL) and net wall hangings (NWH) used alone and in combination with LLINs against multiple insecticide-resistant An. gambiae in Tiassalé, Côte d’Ivoire. Comparison was made to commercial deltamethrin WL and genotypes for kdr and ace-1R resistance were monitored.ResultsThe kdr and ace-1R allele frequencies were 0.83 and 0.44, respectively. Anopheles gambiae surviving discriminating concentrations of deltamethrin and p-methyl in WHO resistance tests were 57 and 96%, respectively. Mortality of free-flying An. gambiae in huts with p-methyl WL and NWH (66 and 50%, respectively) was higher than with pyrethroid WL (32%; P < 0.001). Mortality with LLIN was 63%. Mortality with the combination of LLIN plus p-methyl NWH (61%) or LLIN plus p-methyl WL (73%) did not significantly improve upon the LLIN alone or p-methyl WL or NWH alone. Mosquitoes bearing the ace-1R were more likely to survive exposure to p-methyl WL and NWH. Selection of heterozygote and homozygote ace-1R or kdr genotypes was not less likely after exposure to combined LLIN and p-methyl treatments than to single p-methyl treatment. Blood-feeding rates were lower in huts with the pyrethroid LLIN (19%) than with p-methyl WL (72%) or NWH (76%); only LLIN contributed to personal protection.ConclusionsCombining p-methyl WL or NWH with LLINs provided no improvement in An. gambiae control or personal protection over LLIN alone in southern Côte d’Ivoire; neither did the combination manage resistance. Additional resistance mechanisms to kdr and ace-1R probably contributed to the survival of pyrethroid and organophophate-resistant mosquitoes. The study demonstrates the challenge that malaria control programmes will face if resistance to multiple insecticides continues to spread.

An Experimental Hut Evaluation of PBO-Based and Pyrethroid-Only Nets against the Malaria Vector Anopheles funestus Reveals a Loss of Bed Nets Efficacy Associated with GSTe2 Metabolic Resistance

“…Similar genotype/phenotype studies performed to assess the impact of the knockdown target-site resistance (kdr) on resistance did not reveal such a significant association with blood feeding potentially due to the fact that kdr frequency was already very high in tested An. gambiae population [21]. However, indirect comparison of kdr effect in two separate populations of An.…”

“…Experimental hut studies are the method of choice to evaluate the efficacy of LLINs against mosquito populations using entomological indices as a proxy for potential epidemiological impact [19,20]. It also provides relevant samples to assess how metabolic resistance impacts the effectiveness of LLINs as done previously to assess impact of target site mutations such as kdr [21].…”

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

“…funestus mortality significantly higher for two walls than ceilings only (59 and 39%, respectively)Deterrence increased with increasing coverage (65–77% vs. 92–95% for two walls vs. four walls + ceiling)Four walls + ceilingNo improvement in mosquito mortality when coverage increased beyond two wallsDeltamethrin (55 mg/m 2 )Two wallsTiassalé, Côte d’Ivoire, experimental West African hutsPolyethylene wall lining (WL)Pirimiphos methyl (1 g/m 2 )Four wallsHoled deltamethrin LLIN (PermaNet ® 2.0; 55 mg/m 2 ) An. 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 (&gt...…”

Fenitrothion Bio-Efficacy on Different Intradomicile Surface Types Against Anopheles (Nyssorhynchus) Albimanus in the Main Malaria Endemic Regions of Panama

“…Nevertheless, there exist resistance to organophosphates and carbamates due to the insensitivity to acetylcholinesterase (Achel) that has been reported in some populations of mosquito vectors [37][38]. The malaria vector control programs have encountered multiples problems with resistance that could potentially paralyze the strategies until a new insecticidal molecule is found and is available for their use [39]. Several IRS products are currently available and several are being evaluated by WHO.…”