Malaria remains one of the most debilitating tropical diseases with more than 90% of cases in Africa among children under five and pregnant women. Resistance observed against the main insecticides used in public health sector in major vectors such as Anopheles funestus is threatening the success of vector control interventions. To improve the design of suitable resistance management strategies, it is crucial to elucidate the underlining molecular basis of resistance or cross-resistance between insecticides and also establish patterns of gene flow between populations to predict the speed and direction of spread of resistance genes. To address these questions, this study has investigated the molecular basis of resistance to carbamates and cross/resistance to carbamates/pyrethroids in a population of An. funestus from Malawi. This study has revealed that metabolic resistance is the main mechanism driving carbamate resistance through the over-expression of Cytochrome P450 genes. Genome-wide microarray-based transcription analyses consistently revealed that the duplicated P450 genes CYP6P9a and CYP6P9b were among the most up-regulated genes ( > 2-fold; P < 0.01) in bendiocarb and pyrethroid resistant mosquitoes from Malawi. Other P450 genes were also associated with both carbamates resistance and a carbamates/pyrethroid cross-resistance, including CYP6Z1, CYP9J11. Analysis of polymorphism patterns of CYP6P9a and CYP6P9b genes between resistant and susceptible mosquitoes revealed a correlation with permethrin resistance but not for bendiocarb resistance. In addition a reduced penetration mechanism was shown to be likely involved in carbamate resistance through the elevated expression of several cuticular protein genes. An Africa-wide genetic structure of An. funestus populations was established using microsatellite markers. This study revealed that An. funestus populations from Malawi and Mozambique from southern Africa are genetically closer to each other than the rest of the other African populations from West, Central and East Africa. Two loci AFUB6 and FUNR that are located around same position as the CYP6P9a and CYP6P9b genes on the rp1 QTL on the 2R chromosome are under selection possibly because of pyrethroid resistance due to their low allele number and reduced heterozygosity. Statistical analysis revealed that both loci were under possible selection and sequencing analysis also revealed that CYP6P9a gene is under selection for the resistant An. funestus from southern Africa compared to more susceptible population from Cameroon. The possible cross-resistance observed in this study highlights the need to further elucidate resistance mechanisms before implementing suitable resistance management strategies such as rotation of insecticides to ensure a continued effectiveness of control interventions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:677480 |
| Date | January 2014 |
| Creators | Ndula, Miranda |
| Publisher | University of Liverpool |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://livrepository.liverpool.ac.uk/2027219/ |
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