Abstract
Malaria control programs are being jeopardized by the spread of insecticide resistance in mosquito vector populations. The situation in Burkina Faso is emblematic with Anopheles gambiae populations showing high levels of resistance to most available compounds. Although the frequency of insecticide target-site mutations including knockdown resistance (kdr) and insensitive acetylcholinesterase (Ace-1 R) alleles has been regularly monitored in the area, it is not known whether detoxifying enzymes contribute to the diversity of resistance phenotypes observed in the field. Here, we propose an update on the phenotypic diversity of insecticide resistance in An. gambiae populations sampled from 10 sites in Burkina Faso in 2010. Susceptibility to deltamethrin, permethrin, DDT, bendiocarb and fenithrotion was assessed. Test specimens (N = 30 per locality) were identified to species and molecular form and their genotype at the kdr and Ace-1 loci was determined. Detoxifying enzymes activities including non-specific esterases (NSEs), oxydases (cytochrome P450) and Glutathione S-Transferases (GSTs) were measured on single mosquitoes (N = 50) from each test locality and compared with the An. gambiae Kisumu susceptible reference strain. In all sites, mosquitoes demonstrated multiple resistance phenotypes, showing reduced mortality to several insecticidal compounds at the same time, although with considerable site-to-site variation. Both the kdr 1014L and Ace-1 R 119S resistant alleles were detected in the M and the S forms of An. gambiae, and were found together in specimens of the S form. Variation in detoxifying enzyme activities was observed within and between vector populations. Elevated levels of NSEs and GSTs were widespread, suggesting multiple resistance mechanisms segregate within An. gambiae populations from this country. By documenting the extent and diversity of insecticide resistance phenotypes and the putative combination of their underlying mechanisms in An. gambiae mosquitoes, our work prompts for new alternative strategies to be urgently developed for the control of major malaria vectors in Burkina Faso.
Highlights
Malaria remains one of the most critical public health challenges for Africa despite intense national and international efforts [1]
Mortality rates below the 80% threshold were recorded for bendiocarb in all localities within the cotton-intensive cultivation belt in the south-western part of our study area (i.e., Banfora, Orodara, Tiefora, Samblatoukoro and Soumousso) except in the rice-fields area of VK7 where the vector population seems still completely susceptible to this insecticide
In Burkina Faso, country-wide surveys associating insecticide susceptibility tests and molecular assays for the detection of mutations associated with insecticide resistance have been ongoing since 1999 [11,30,44,56]
Summary
Malaria remains one of the most critical public health challenges for Africa despite intense national and international efforts [1]. Recent studies have confirmed that resistance to DDT is still prevailing at a high level in An. gambiae populations from Burkina Faso, where resistance to pyrethroids was increasingly reported [9,10,11]. Pyrethroid insecticides are the most widely used compounds in public health because of their high effectiveness and strong excito-repellent effect on insects, as well as low mammalian toxicity [12,13]. Resistance to this insecticide class is widespread in An. gambiae [9,10,14,15]. The knock-down resistance (kdr) mutation, changing a Leucine (TTA) to a Phenylalanine (TTT) at position 1014 of the voltagegated sodium channel gene (i.e. L1014F mutation) was predominant in West and Central African An. gambiae populations [9,17] whereas another substitution, changing the Leucine (TTA) to a Serine (TCA) at position 1014 (i.e. L1014S mutation) originated from Kenya [18], has spread into Central Africa including
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