Abstract
BackgroundHigh coverage of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the cornerstones of vector control strategy in Senegal where insecticide resistance by the target vectors species is a great of concern. This study explores insecticide susceptibility profile and target-site mutations mechanisms within the Anophelesgambiae complex in southeastern Senegal.MethodsLarvae of Anopheles spp. were collected in two sites from southeastern Senegal Kedougou and Wassadou/Badi in October and November 2014, and reared until adult emergence. Wild F0 adult mosquitoes were morphologically identified to species. Susceptibility of 3–5-day-old An. gambiae (s.l.) samples to 11 insecticides belonging to the four insecticide classes was assessed using the WHO insecticide susceptibility bioassays. Tested samples were identified using molecular techniques and insecticide resistance target-site mutations (kdr, ace-1 and rdl) were determined.ResultsA total of 3742 An.gambiae (s.l.) were exposed to insecticides (2439 from Kedougou and 1303 from Wassadou-Badi). Tests with pyrethroid insecticides and DDT showed high level of resistance in both Kedougou and Wassadou/Badi. Resistance to pirimiphos-methyl and malathion was not detected while resistance to bendoicarb and fenitrothion was confirmed in Kedougou. Of the 745 specimens of An.gambiae (s.l.) genotyped, An.gambiae (s.s.) (71.6%) was the predominant species, followed by An.arabiensis (21.7%), An.coluzzii (6.3%) and hybrids (An. gambiae (s.s.)/An.coluzzii; 0.4%). All target site mutations investigated (Vgsc-1014F, Vgsc-1014S, Ace-1 and Rdl) were found at different frequencies in the species of the Anophelesgambiae complex. Vgsc-1014F mutation was more frequent in An.gambiae (s.s.) and An.coluzzii than An.arabiensis. Vgsc-1014S was present in An.gambiae (s.l.) populations in Wassadou but not in Kedougou. Ace-1 and rdl mutations were more frequent in An.gambiae (s.s.) in comparison to An.arabiensis and An.coluzzii.ConclusionsResistance to all the four insecticide classes tested was detected in southeastern Senegal as well as all target site mutations investigated were found. Data will be used by the national Malaria Control Programme.
Highlights
High coverage of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the cornerstones of vector control strategy in Senegal where insecticide resistance by the target vectors species is a great of concern
The aims of this study were to update the current status of insecticide resistance among An. gambiae (s.l.) populations in southeastern Senegal and to identify the mechanisms of insecticide resistance, for target-site mutations involved in insecticide resistance
Susceptibility tests A total of 3742 specimens of the An. gambiae complex were exposed to the World Health Organization (WHO) recommended diagnostic doses (2439 from Kedougou and 1303 from Wassadou-Badi)
Summary
High coverage of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) are the cornerstones of vector control strategy in Senegal where insecticide resistance by the target vectors species is a great of concern. Malaria remains a major public health challenge in endemic countries It mainly affects vulnerable groups, including pregnant women and children less than five years-old. The number of malaria cases has decreased from 251 million in 2010 to 228 million in 2018 At the same time, the disease incidence declined from 71 to 57 cases per 1000 in 2010 and 2018, respectively [1] Despite these advances, malaria incidence in Africa has increased between 2014 and 2016 [2], because of factors including the development and spread of insecticide resistance in the main malaria vectors, such as An. funestus and An. gambiae (s.l.). Resistance to pyrethroids (the only insecticide class currently approved for long-lasting insecticidal mosquito nets: LLINs) [3, 5, 6] and to DDT (dichlorodiphenyltrichloroethane) [7] has been reported in many endemic settings [8, 9], in Asia and in tropical African countries
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