Abstract
BackgroundThe widespread emergence of resistance to pyrethroids is a major threat to the gains made in malaria control. To monitor the presence and possible emergence of resistance against a variety of insecticides used for malaria control in Rwanda, nationwide insecticide resistance surveys were conducted in 2011 and 2013.MethodsLarvae of Anopheles gambiae sensu lato mosquitoes were collected in 12 sentinel sites throughout Rwanda. These were reared to adults and analysed for knock-down and mortality using WHO insecticide test papers with standard diagnostic doses of the recommended insecticides. A sub-sample of tested specimens was analysed for the presence of knockdown resistance (kdr) mutations.ResultsA total of 14,311 mosquitoes were tested and from a sample of 1406 specimens, 1165 (82.9%) were identified as Anopheles arabiensis and 241 (17.1%) as Anopheles gambiae sensu stricto. Mortality results indicated a significant increase in resistance to lambda-cyhalothrin from 2011 to 2013 in 83% of the sites, permethrin in 25% of the sites, deltamethrin in 25% of the sites and DDT in 50% of the sites. Mosquitoes from 83% of the sites showed full susceptibility to bendiocarb and 17% of sites were suspected to harbour resistance that requires further confirmation. No resistance was observed to fenitrothion in all study sites during the entire survey. The kdr genotype results in An. gambiae s.s. showed that 67 (50%) possessed susceptibility (SS) alleles, while 35 (26.1%) and 32 (23.9%) mosquitoes had heterozygous (RS) and homozygous (RR) alleles, respectively. Of the 591 An. arabiensis genotyped, 425 (71.9%) possessed homozygous (SS) alleles while 158 (26.7%) and 8 (1.4%) had heterozygous (RS) and homozygous (RR) alleles, respectively. Metabolic resistance involving oxidase enzymes was also detected using the synergist PBO.ConclusionThis is the first nationwide study of insecticide resistance in malaria vectors in Rwanda. It shows the gradual increase of insecticide resistance to pyrethroids (lambda-cyhalothrin, deltamethrin, permethrin) and organochlorines (DDT) and the large presence of target site insensitivity. The results demonstrate the need for Rwanda to expand monitoring for insecticide resistance including further metabolic resistance testing and implement an insecticide resistance management strategy to sustain the gains made in malaria control.
Highlights
The widespread emergence of resistance to pyrethroids is a major threat to the gains made in malaria control
The Rwanda Malaria Indicator Survey carried out in 2013 showed that overall long-lasting insecticide-treated net (LLIN) coverage is high with 83% of the households owning at least one LLIN and 74% reported to have slept under a LLIN the previous night for pregnant women and children under five [8]
Morphological and molecular identification A total of 14,311 mosquitoes tested for insecticide resistance was morphologically identified as An. gambiae s.l
Summary
The widespread emergence of resistance to pyrethroids is a major threat to the gains made in malaria control. It has been estimated that since 2000 more than 670 million cases of malaria have been averted by combining IRS and LLINs with case management and community education [4, 5]. In Rwanda, the national scale-up of vector control interventions has contributed to a steady reduction of malaria cases from 1.6 million in 2005 to 472,000 cases in 2012 [6, 7]. This reduction has been attributed to the combined effects of universal coverage with LLINs [7] and targeted IRS operations in districts with the highest malaria endemicity (5 out of 30 districts) based on epidemiologic and entomologic data. From 2005 to 2013, the National Malaria Control Programme (NMCP) of the Rwanda Ministry of Health has distributed approximately 11.2 million LLINs to a population of an estimated 11 million people [9]
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