Impact of three years of large scale Indoor Residual Spraying (IRS) and Insecticide Treated Nets (ITNs) interventions on insecticide resistance in Anopheles gambiae s.l. in Benin

Abstract

BackgroundIn Benin, Indoor Residual Spraying (IRS) and long-lasting insecticidal nets (LLINs) are the cornerstones of malaria prevention. In the context of high resistance of Anopheles gambiae to pyrethroids, The National Malaria Control Program (NMCP) has undertaken a full coverage of IRS in a no-flood zone in the Oueme region, coupled with the distribution of LLINs in a flood zone. We assessed the impact of this campaign on phenotypic resistance, kdr (knock-down resistance) and ace-1R (insensitive acetylcholinesterase) mutations.MethodsInsecticides used for malaria vector control interventions were bendiocarb WP (0.4 g/m2) and deltamethrin (55 mg/m2), respectively for IRS and LLINs. Susceptibility status of An. gambiae was assessed using World Health Organization bioassay tests to DDT, permethrin, deltamethrin and bendiocarb in the Oueme region before intervention (2007) and after interventions in 2008 and 2010. An. gambiae specimens were screened for identification of species, molecular M and S forms and for the detection of the West African kdr (L1014F) as well as ace-1R mutations using PCR techniques.ResultsThe univariate logistic regression performed showed that kdr frequency has increased significantly during the three years in the intervention area and in the control area. Several factors (LLINs, IRS, mosquito coils, aerosols, use of pesticides for crop protection) could explain the selection of individual resistant An. gambiae. The Kdr resistance gene could not be the only mechanism of resistance observed in the Oueme region. The high susceptibility to bendiocarb is in agreement with a previous study conducted in Benin. However, the occurrence of ace-1R heterozygous individuals even on sites far from IRS areas, suggests other factors may contribute to the selection of resistance other than those exerted by the vector control program.ConclusionThe results of this study have confirmed that An.gambiae have maintained and developed the resistance to pyrethroids, but are still susceptible to bendiocarb. Our data clearly shows that selection of resistant individuals was caused by other insecticides than those used by the IRS and LLINs.

Insecticide Resistance Allele Frequencies in Anopheles gambiae before and after Anti-Vector Interventions in Continental Equatorial Guinea

“…17 In a recent study on the impact of a large scale IRS and ITN campaign in southern Benin, kdr frequencies were also found to have increased, although this was also true for areas in which no planned interventions were implemented, underscoring the effect of the agricultural and household insecticide use on resistance. 18 In east Africa, a similar increase has been observed. For example, in Uganda where DDT is used for IRS and deltamethrin-impregnated ITNs are the cornerstone of vector suppression efforts, a significant increase in L1014S frequencies was observed in An.…”

“…gambiae populations by use of pyrethroid insecticides in anti-malarial interventions also reported in other studies. 16,18,22 Interestingly, if the combined pre-intervention frequency of L1014S and L1014F was high, L1014S frequencies decreased after the start of the intervention. These observations strongly suggest that L1014S can increase at the expense of the susceptible L1014L allele, but that it tends to decrease when competing primarily with L1014F.…”

A New Long-Lasting Indoor Residual Formulation of the Organophosphate Insecticide Pirimiphos Methyl for Prolonged Control of Pyrethroid-Resistant Mosquitoes: An Experimental Hut Trial in Benin

“…There is an urgent need to find alternative insecticides to pyrethroids and DDT in order to maintain the two pronged attack of IRS and LLIN against malaria while simultaneously reducing the selection pressure for pyrethroid resistance. The President’s Malaria Initiative is using the carbamate bendiocarb for IRS in countries where pyrethroid resistance is prevalent [4]–[5], [33]–[35]. The problem with carbamate insecticides is their short residual life, which means having to spray twice per year in countries where malaria transmission seasons are longer than the 2–3 month residual lifespan of the carbamate, as occurs in many sub-Saharan countries [36]–[37].…”

“…In areas of seasonal transmission, prone to epidemics, IRS has the advantage of protecting entire populations at risk [2], [3]. In holendemic areas of more stable transmission two or more spray rounds of IRS may be required to cover the full transmission season [4], [5]. Spiralling costs of recurrent campaigns may make IRS with conventional formulations harder to justify or sustain [6].…”

Evidence of multiple insecticide resistance mechanisms in Anopheles gambiae populations in Bangui, Central African Republic

“…Today, the main approaches of malaria control rely on the early detection of cases by the rapid diagnostic tests (RDTs), the prompt treatment of malaria cases with artemisinin based combination therapy (ACT) and vector control strategies. The combined actions of vector control tools, including indoor residual spraying (IRS) and insecticide-treated nets (ITN), have significantly reduced the burden of malaria in many parts of the world giving hope to elimination or pre-elimination malaria programmes [5, 6]. However, the rapid and widespread insecticide resistance represents a serious threat to the ambitious goal of malaria elimination [7].…”