High insecticide resistance intensity of Anopheles gambiae (s.l.) and low efficacy of pyrethroid LLINs in Accra, Ghana
Date
2019-06-05
Journal Title
Journal ISSN
Volume Title
Publisher
Parasites & Vectors
Abstract
Background: Insecticide 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.
Methods: Three- 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.
Results: Anopheles 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%.
Conclusions: WHO 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.
Keywords: Anopheles gambiae (s.l.), WHO susceptibility
Description
Research Article
Keywords
Anopheles gambiae (s.l.), WHO susceptibility test, CDC bottle assay, Intensity assay, Insecticide resistance