Distribution of ace-1R and resistance to carbamates and organophosphates in Anopheles gambiae s.s. populations from Côte d'Ivoire

Institut Pierre Richet, BP 47 Abidjan, Côte d'Ivoire.
Malaria Journal (Impact Factor: 3.11). 06/2010; 9(1):167. DOI: 10.1186/1475-2875-9-167
Source: PubMed


The spread of pyrethroid resistance in Anopheles gambiae s.s. is a critical issue for malaria vector control based on the use of insecticide-treated nets. Carbamates and organophosphates insecticides are regarded as alternatives or supplements to pyrethroids used in nets treatment. It is, therefore, essential to investigate on the susceptibility of pyrethroid resistant populations of An. gambiae s.s. to these alternative products.
In September 2004, a cross sectional survey was conducted in six localities in Côte d'Ivoire: Toumbokro, Yamoussoukro, Toumodi in the Southern Guinea savannah, Tiassalé in semi-deciduous forest, then Nieky and Abidjan in evergreen forest area. An. gambiae populations from these localities were previously reported to be highly resistant to pyrethroids insecticides. Anopheline larvae were collected from the field and reared to adults. Resistance/susceptibility to carbamates (0.4% carbosulfan, 0.1% propoxur) and organophosphates (0.4% chlorpyrifos-methyl, 1% fenitrothion) was assessed using WHO bioassay test kits for adult mosquitoes. Then, PCR assays were run to determine the molecular forms (M) and (S), as well as phenotypes for insensitive acetylcholinesterase (AChE1) due to G119S mutation.
Bioassays showed carbamates (carbosulfan and propoxur) resistance in all tested populations of An. gambiae s.s. In addition, two out of the six tested populations (Toumodi and Tiassalé) were also resistant to organophosphates (mortality rates ranged from 29.5% to 93.3%). The M-form was predominant in tested samples (91.8%). M and S molecular forms were sympatric at two localities but no M/S hybrids were detected. The highest proportion of S-form (7.9% of An. gambiae identified) was in sample from Toumbokro, in the southern Guinea savannah. The G119S mutation was found in both M and S molecular forms with frequency from 30.9 to 35.2%.
This study revealed a wide distribution of insensitive acetylcholinesterase due to the G119S mutation in both M and S molecular forms of the populations of An. gambiae s.s. tested. The low cross-resistance between carbamates and organophosphates highly suggests involvement of other resistance mechanisms such as metabolic detoxification or F290V mutation.

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    • "This study provides a wider view of the spread of insecticide resistance in Côte d'Ivoire and adds a significant baseline knowledge to recent reports of high insecticide resistance levels in M'Bé [19], Yaokoffikro [20] near Bouaké in central Côte d'Ivoire, Tiassalé [18], [33] and Adzopé [17] in southern Côte d'Ivoire. All these reports including the present highlight the level of spread of resistance to all class of insecticides deployed for vector control, either as LLIN already in place or IRS under consideration for implementation in Côte d'Ivoire; an increasing trend commonly shared by several countries in West Africa[34]–[39]. "
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    ABSTRACT: Insecticide resistance constitutes a major threat that may undermine current gain in malaria control in most endemic countries. National Malaria Control Programmes (NMCPs) need as much information as possible on the resistance status of malaria vectors and underlying mechanisms in order to implement the most relevant and efficient control strategy. Bioassays, biochemical and molecular analysis were performed on An. gambiae collected in six sentinel sites in Côte d'Ivoire. The sites were selected on the basis of their bioclimatic status and agricultural practices. An. gambiae populations across sites showed high levels of resistance to organochloride, pyrethroid and carbamate insecticides. The kdr and ace-1(R) mutations were detected in almost all sentinel sites with mosquitoes on the coastal and cotton growing areas mostly affected by these mutations. At almost all sites, the levels of detoxifying enzymes (mixed-function oxidases (MFOs), non-specific esterases (NSE) and glutathione-S-transferases (GSTs)) in An. gambiae populations were significantly higher than the levels found in the susceptible strain Kisumu. Pre-exposure of mosquitoes to PBO, an inhibitor of MFOs and NSEs, significantly increased mortality rates to pyrethroids and carbamates in mosquitoes but resistance in most cases was not fully synergised by PBO, inferring a residual role of additional mechanisms, including kdr and ace-1 site insensitivity. The large distribution of resistance in Côte d'Ivoire raises an important question of whether to continue to deploy pyrethroid-based long-lasting insecticidal nets (LLINs) and insecticide residual spraying (IRS) towards which resistance continues to rise with no guarantee that the level of resistance would not compromise their efficacy. Innovative strategies that combine insecticide and synergists in LLINs or spatially LLIN and an effective non-pyrethroid insecticide for IRS could be in the short term the best practice for the NMCP to manage insecticide resistance in malaria vectors in Côte d'Ivoire and other endemic countries facing resistance.
    Full-text · Article · Dec 2013 · PLoS ONE
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    • "The predictive value for heterozygotes was much more moderate, and allelic sensitivity was much poorer than specificity. Ace-1 119S frequency was highly variable across southern Ghana, being absent from some samples but present in Ashaiman at the highest frequency yet recorded, far exceeding a report of 50% from Côte d’lvoire [15]. Both the logistic regression and Mantel test analyses indicated that Ace-1 119S frequency acts as a strong independent predictor of mortality to bendiocarb. "
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    ABSTRACT: With high DDT resistance present throughout much of West Africa, carbamates and organophosphates are increasingly important alternatives to pyrethroids for indoor residual spraying (IRS). Though less widespread, resistance to both of these alternative insecticide classes has also been documented within the Anopheles gambiae species pair (formerly the M and S molecular forms) in West Africa. To manage insecticide efficacy, it is important to predict how and where resistance is likely to occur and spread, which could be aided by using molecular diagnostics with high predictive value. Anopheles coluzzii and An. gambiae s.s. were collected from 18 sites throughout southern Ghana and bioassayed with bendiocarb, the most commonly applied carbamate, and an organophosphate, fenitrothion. The Ace-1 target site substitution G119S was genotyped by qPCR. Fenitrothion induced higher mortality than bendiocarb, though phenotypes correlated strongly across populations. Ace-1 119S was found at much higher frequency in An. gambiae s.s than An. coluzzii, exceeding 90 % in a population from Greater Accra, the highest frequency reported to date. Ace-1 G119S was very strongly associated with resistance to both insecticides, providing high predictive power for diagnosis, though with some evidence for a differential effect between molecular forms for bendiocarb. Sequencing of the gene revealed a lack of variation in resistant alleles precluding determination of origin, but Ace-1 copy number variation was detected for the first time in Ghana. The results validate the utility of G119S as a useful diagnostic of organophosphate and carbamate resistance within and among populations, whilst highlighting the potential for an aggregate nature of Ace-1 genotypes, which may comprise both single-copy and duplicated genes. Further work is now required to determine the distribution and resistance-association of Ace-1 duplication.
    Full-text · Article · Nov 2013 · Malaria Journal
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    • "population (Chouaibou et al., 2012; Edi et al., 2012). The target site mutations that confer crossresistance to DDT and pyrethroids (kdr), and those implicated in resistance to carbamates and organophosphates (modified acetylcholinesterase , Ace-IR) have also been previously detected in this population (Chouaibou et al., 2012; Edi et al., 2012; Alou et al., 2010). Only a low and non-significant activity of P-gps was seen in this study, although it is important to note that recent reports indicate that verapamil can inhibit some P450s. "
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    ABSTRACT: Metabolic resistance and the potential role of permeability -glycoprotein (P-gp) efflux pumps were investigated in a pyrethroid-resistant wild Anopheles gambiae s.l. Tiassalé population, using WHO susceptibility assays with deltamethrin (0.05%), with and without pre-exposure to synergists. The synergists used included an inhibitor of P-glycoprotein efflux pumps (verapamil), an inhibitor of esterases (EN 16-5), and an inhibitor of P450s and esterases (piperonyl butoxide). Pre-exposure to verapamil followed by deltamethrin led to a slight but non-significant (P=0.59) increase in mortality relative to exposure to deltamethrin alone (64.5% versus 69.2%). Similarly, pre-exposure to EN 16-5 yielded a non-significant increase in mortality (to 76.6%; P=0.85) but a significant increase in the knock down rate (from 48.3% to 78.7%; P<0.01). Pre-exposure with PBO caused a significant increase in mortality (to 93.1%; P<0.001) and knockdown rate (100%; P<0.001), which related to a 2.9 fold decrease in the resistance level. The results provide evidence that metabolic resistance mechanisms are present within the assessed mosquito population. The decrease in time to knock down of this population with deltamethrin following exposure to EN16-5 and PBO is of particular relevance to vector control, where quick knock down is a highly desired characteristic. The suspected resistance mechanisms present in this population merit further investigation through biochemical and molecular analyses for full resistance profile characterization. Bioassays with synergists can provide a quick and easy basis for initial characterization of resistant mosquito populations, without the need of preserved specimens, expensive equipment and substrates or specialized expertise.
    Full-text · Article · Nov 2013 · Acta tropica
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