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      Exploring Mechanisms of Multiple Insecticide Resistance in a Population of the Malaria Vector Anopheles funestus in Benin

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          Abstract

          Background

          The insecticide resistance status of the malaria vector Anopheles funestus and the underlying resistance mechanisms remain uncharacterised in many parts of Africa, notably in Benin, West Africa. To fill this gap in our knowledge, we assessed the susceptibility status of a population of this species in Pahou, Southern Benin and investigated the potential resistance mechanisms.

          Methodology/Principal Findings

          WHO bioassays revealed a multiple resistance profile for An. funestus in Pahou. This population is highly resistant to DDT with no mortality in females after 1h exposure to 4%DDT. Resistance was observed against the Type I pyrethroid permethrin and the carbamate bendiocarb. A moderate resistance was detected against deltamethrin (type II pyrethroids). A total susceptibility was observed against malathion, an organophosphate. Pre-exposure to PBO did not change the mortality rates for DDT indicating that cytochrome P450s play no role in DDT resistance in Pahou. No L1014F kdr mutation was detected but a correlation between haplotypes of two fragments of the Voltage-Gated Sodium Channel gene and resistance was observed suggesting that mutations in other exons may confer the knockdown resistance in this species. Biochemical assays revealed elevated levels of GSTs and cytochrome mono-oxygenases in Pahou. No G119S mutation and no altered acetylcholinesterase gene were detected in the Pahou population. qPCR analysis of five detoxification genes revealed that the GSTe2 is associated to the DDT resistance in this population with a significantly higher expression in DDT resistant samples. A significant over-expression of CYP6P9a and CYP6P9b previously associated with pyrethroid resistance was also seen but at a lower fold change than in southern Africa.

          Conclusion

          The multiple insecticide resistance profile of this An. funestus population in Benin shows that more attention should be paid to this important malaria vector for the implementation and management of current and future malaria vector control programs in this country.

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          A cocktail polymerase chain reaction assay to identify members of the Anopheles funestus (Diptera: Culicidae) group.

          L Koekemoer, L Kamau, R H Hunt … (2002)
          Anopheles funestus Giles is a major malaria vector in Africa belonging to a group of species with morphologically similar characteristics. Morphological identification of members of the A. funestus group is difficult because of overlap of distinguishing characteristics in adult or immature stages as well as the necessity to rear isofemale lines to examine larval and egg characters. A rapid rDNA polymerase chain reaction (PCR) method has been developed to accurately identify five members of the A. funestus group. This PCR is based on species-specific primers in the ITS2 region on the rDNA to identify A. funestus (approximately 505bp), Anopheles vaneedeni Gillies and Coetzee (approximately 587bp), Anopheles rivulorum Leeson (approximately 411bp), Anopheles leesoni Evans (approximately 146bp), and Anopheles parensis Gillies (approximately 252bp).
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            Identification of a point mutation in the voltage-gated sodium channel gene of Kenyan Anopheles gambiae associated with resistance to DDT and pyrethroids.

            H Ranson, B. Jensen, J. Vulule … (2000)
            A field trial of permethrin-impregnated bednets and curtains was initiated in Western Kenya in 1990, and a strain of Anopheles gambiae showing reduced susceptibility to permethrin was colonized from this site in 1992. A leucine-phenylalanine substitution at position 1014 of the voltage-gated sodium channel is associated with resistance to permethrin and DDT in many insect species, including Anopheles gambiae from West Africa. We cloned and sequenced a partial sodium channel cDNA from the Kenyan permethrin-resistant strain and we identified an alternative substitution (leucine to serine) at the same position, which is linked to the inheritance of permethrin resistance in the F(2) progeny of genetic crosses between susceptible and resistant individuals. The diagnostic polymerase chain reaction (PCR) developed by Martinez-Torres et al. [(1998) Insect Mol Biol 7: 179-184] to detect kdr alleles in field populations of An. gambiae will not detect the Kenyan allele and hence reliance on this assay may lead to an underestimate of the prevalence of pyrethroid resistance in this species. We adapted the diagnostic PCR to detect the leucine-serine mutation and with this diagnostic we were able to demonstrate that this kdr allele was present in individuals collected from the Kenyan trial site in 1986, prior to the introduction of pyrethroid-impregnated bednets. The An. gambiae sodium channel was physically mapped to chromosome 2L, division 20C. This position corresponds to the location of a major quantitative trait locus determining resistance to permethrin in the Kenyan strain of An. gambiae.
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              A ribosomal RNA gene probe differentiates member species of the Anopheles gambiae complex.

              F Collins, M. A. Mendez, M. O. Rasmussen … (1987)
              A 0.59 kilobase DNA fragment cloned from an rDNA cistron of the mosquito Anopheles gambiae can be used as a probe to differentiate between A. gambiae, A. arabiensis, and A. melas, three morphologically identical sibling species in the A. gambiae complex which otherwise can be reliably distinguished only by polytene chromosome banding patterns. Although all are important (and often sympatric) African malaria vectors, their relative roles in malaria transmission have thus far been difficult to assess. The probe, an EcoRI-SalI fragment from the 3' end of the 28S beta coding region of the cistron, is present in all three species, but the species differ uniquely with respect to the location of an EcoRI site in the nontranscribed spacer (NTS) downstream of the fragment. We have routinely used the probe to identify A. gambiae complex mosquitoes to species on the basis of genomic DNA extracted from individual air dried specimens. A single mosquito abdomen provides more than sufficient DNA for the assay, and neither eggs nor a bloodmeal in the abdomen interfere with DNA yield. Moreover, the DNA extraction procedure does not degrade the bloodmeal IgG, so the residual protein pellet can be used to identify the mosquito bloodmeal source. Since the rDNA cistron organization as detected by the probe does not differ between male and female mosquitoes, the probe can be used for either sex. Preliminary experiments show that the probe is equally useful for mosquito larvae and pupae.
              Article 0 comments Cited 186 times – based on 0 reviews     Review now
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                Author and article information

                Contributors
                : Role: Editor
                Journal
                Journal ID (nlm-ta): PLoS One
                Journal ID (publisher-id): plos
                Journal ID (pmc): plosone
                Title: PLoS ONE
                Publisher: Public Library of Science (San Francisco, USA )
                ISSN (Electronic): 1932-6203
                Publication date Collection: 2011
                Publication date (Electronic): 16 November 2011
                Volume: 6
                Issue: 11
                Electronic Location Identifier: e27760
                Affiliations
                [1 ]International Institute of Tropical Agriculture, Cotonou, Benin
                [2 ]Liverpool School of Tropical Medicine, Liverpool, United Kingdom
                [3 ]Bayero University, Kano, Nigeria
                New Mexico State University, United States of America
                Author notes

                Conceived and designed the experiments: CSW. Performed the experiments: RD HI ZT CSW. Analyzed the data: CSW. Wrote the paper: CSW RD.

                Article
                Publisher ID: PONE-D-11-13559
                DOI: 10.1371/journal.pone.0027760
                PMC ID: 3218031
                PubMed ID: 22110757
                SO-VID: 7e26a0e1-e2b6-4ef2-800d-426b0f19ab4e
                Copyright © Djouaka et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
                History
                Date received : 15 July 2011
                Date accepted : 24 October 2011
                Page count
                Pages: 10
                Categories
                Subject: Research Article
                Subject: Biology
                Subject: Computational Biology
                Subject: Population Genetics
                Subject: Evolutionary Biology
                Subject: Population Genetics
                Subject: Genetics
                Subject: Gene Expression
                Subject: Population Genetics
                Subject: Microbiology
                Subject: Vector Biology
                Subject: Anopheles
                Subject: Population Biology
                Subject: Population Dynamics
                Subject: Population Genetics
                Subject: Medicine
                Subject: Infectious Diseases
                Subject: Vectors and Hosts
                Subject: Anopheles

                ScienceOpen disciplines: Uncategorized
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                ScienceOpen disciplines: Uncategorized

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