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Acetylcholinesterase (Ace-1) target site mutation 119S is strongly diagnostic of carbamate and organophosphate resistance in Anopheles gambiae s.s. and Anopheles coluzzii across southern Ghana.

Essandoh J, Yawson AE, Weetman D - Malar. J. (2013)

Bottom Line: 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.The results validate 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Liverpool School of Tropical Medicine, Liverpool, UK. dweetman@liv.ac.uk.

ABSTRACT

Background: 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.

Methods: 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.

Results: 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.

Conclusions: The results validate 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.

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Related in: MedlinePlus

Map of southern Ghana showing the study sites (1-18) across administrative regions (I-V).
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Figure 1: Map of southern Ghana showing the study sites (1-18) across administrative regions (I-V).

Mentions: Mosquitoes were sampled from 18 sites spanning five distinct ecological zones in southern Ghana (Figure 1). Study sites were classified qualitatively based on settlement (rural, peri-urban and urban), and specific agricultural activities (irrigation, semi-irrigation and dry cultivation) that lead to creation of mosquito breeding sites as well as deployment of agricultural insecticides (Additional file 1). Anopheles gambiae larvae were collected from early March to mid-August 2011 from urban, peri-urban and rural settings. The larvae were collected from a variety of habitats such as pools, puddles, drainage channels, irrigations, and rice fields by the dipping method. Larvae were fed with ground Tetramin fish-food and upon pupation were transferred to a cage to emerge into adults. Cotton wool pads soaked with 10 % sugar solution were used to feed the adult mosquitoes. Male mosquitoes were removed from cages daily so as to avoid mating.


Acetylcholinesterase (Ace-1) target site mutation 119S is strongly diagnostic of carbamate and organophosphate resistance in Anopheles gambiae s.s. and Anopheles coluzzii across southern Ghana.

Essandoh J, Yawson AE, Weetman D - Malar. J. (2013)

Map of southern Ghana showing the study sites (1-18) across administrative regions (I-V).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3842805&req=5

Figure 1: Map of southern Ghana showing the study sites (1-18) across administrative regions (I-V).
Mentions: Mosquitoes were sampled from 18 sites spanning five distinct ecological zones in southern Ghana (Figure 1). Study sites were classified qualitatively based on settlement (rural, peri-urban and urban), and specific agricultural activities (irrigation, semi-irrigation and dry cultivation) that lead to creation of mosquito breeding sites as well as deployment of agricultural insecticides (Additional file 1). Anopheles gambiae larvae were collected from early March to mid-August 2011 from urban, peri-urban and rural settings. The larvae were collected from a variety of habitats such as pools, puddles, drainage channels, irrigations, and rice fields by the dipping method. Larvae were fed with ground Tetramin fish-food and upon pupation were transferred to a cage to emerge into adults. Cotton wool pads soaked with 10 % sugar solution were used to feed the adult mosquitoes. Male mosquitoes were removed from cages daily so as to avoid mating.

Bottom Line: 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.The results validate 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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Liverpool School of Tropical Medicine, Liverpool, UK. dweetman@liv.ac.uk.

ABSTRACT

Background: 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.

Methods: 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.

Results: 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.

Conclusions: The results validate 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.

Show MeSH
Related in: MedlinePlus