Abstract
BackgroundInsecticide resistance of Anopheles gambiae (s.l.) against public health insecticides is increasingly reported in Ghana and need to be closely monitored. This study investigated the intensity of insecticide resistance of An. gambiae (s.l.) found in a vegetable growing area in Accra, Ghana, where insecticides, herbicides and fertilizers are massively used for plant protection. The bioefficacy of long-lasting insecticidal nets (LLINs) currently distributed in the country was also assessed to delimitate the impact of the insecticide resistance intensity on the effectiveness of those nets.MethodsThree- to five-day-old adult mosquitoes that emerged from collected larvae from Opeibea, Accra (Ghana), were assayed using CDC bottle and WHO tube intensity assays against different insecticides. The Vgsc-L1014F and ace-1 mutations within the population were also characterized using PCR methods. Furthermore, cone bioassays against different types of LLINs were conducted to evaluate the extent and impact of the resistance of An. gambiae (s.l.) from Opeibea.ResultsAnopheles gambiae (s.l.) from Opeibea were resistant to all the insecticides tested with very low mortality observed against organochlorine, carbamates and pyrethroid insecticides using WHO susceptibility tests at diagnostic doses during three consecutive years of monitoring. The average frequencies of Vgsc-1014F and ace-1 in the An. gambiae (s.l.) population tested were 0.99 and 0.76, respectively. The intensity assays using both CDC bottle and WHO tubes showed high resistance intensity to pyrethroids and carbamates with survivals at 10× the diagnostic doses of the insecticides tested. Only pirimiphos methyl recorded a low resistance intensity with 100% mortality at 5× the diagnostic dose. The bioefficacy of pyrethroid LLINs ranged from 2.2 to 16.2% mortality while the PBO LLIN, PermaNet® 3.0, was 73%.ConclusionsWHO susceptibility tests using the diagnostic doses described the susceptibility status of the mosquito colony while CDC bottle and WHO tube intensity assays showed varying degrees of resistance intensity. Although both methods are not directly comparable, the indication of the resistance intensity showed the alarming insecticide resistance intensity in Opeibea and its surroundings, which could have an operational impact on the efficacy of vector control tools and particularly on pyrethroid LLINs.
Highlights
Insecticide resistance of Anopheles gambiae (s.l.) against public health insecticides is increasingly reported in Ghana and need to be closely monitored
Most malaria vector control strategies currently rely on the use of long-lasting insecticidal nets (LLINs) and/ or indoor residual spraying (IRS) of insecticides, of which Ghana is no exception [4, 5]
World Health Organization (WHO) susceptibility tests and intensity assays One hundred percent mortality was recorded for all insecticide impregnated papers tested against the susceptible strain of An. gambiae (s.s.) Kisumu during the three consecutive years, confirming the good quality of the insecticide impreganted papers used (Additional file 1: Table S1)
Summary
Insecticide resistance of Anopheles gambiae (s.l.) against public health insecticides is increasingly reported in Ghana and need to be closely monitored. Most malaria vector control strategies currently rely on the use of long-lasting insecticidal nets (LLINs) and/ or indoor residual spraying (IRS) of insecticides, of which Ghana is no exception [4, 5]. Both vector control measures have largely involved the use of pyrethroid insecticides for LLINs and all the classes of insecticides for IRS. According to IR Mapper [6], 96% of countries where pyrethroid testing was conducted between 2010 and 2017 confirmed resistance. Increasing resistance intensity is reported in some of these areas [7, 8], implying the need to regularly monitor the resistance status including resistance intensity of vector populations in countries
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