Abstract
BackgroundMembers of the Anopheles gambiae (s.l.) complex are one of the major vectors of malaria in Africa. LLINs and IRS are the most effective tools used in vector control of malaria. However, their effectiveness may be hampered by the development and spread of insecticide resistance in the target vectors species. The objective of this study was to assess the susceptibility of Anopheles gambiae (s.l.) mosquitoes from South-West Cameroon to deltamethrin, permethrin and to malathion, four years after the mass deployment of LLINs.MethodsAnopheles larvae were collected from Limbe, Tiko and Buea, three cities of the Fako division and reared until adult emergence. Adult mosquitoes from field larvae were identified as belonging to the Anopheles gambiae (s.l.) complex using standard identification keys. Susceptibility of mosquito samples to deltamethrin, permethrin and malathion was assessed using WHO susceptibility tests protocol for adult mosquitoes. Molecular identification of tested samples was performed using the PCR SINE200 protocol and by PCR-RFLP. The kdr alleles were genotyped using the hot ligation oligonucleotide assay (HOLA).ResultsTwo species of the An. gambiae (s.l.) complex, An. coluzzii and An. gambiae (s.s.) were identified in all three study locations with high proportions of An. coluzzii in Limbe (84.06%) and Tiko (92.2%), while in Buea, An. coluzzii (55.6%) and An. gambiae (s.s.) (44.4%) occurred almost in the same proportions. Tested samples were found resistant to pyrethroids (deltamethrin and permethrin) in all locations (< 90% mortality), with > 3-fold increase of KDT50 values compared with the Kisumu susceptible reference strain of An. gambiae (s.s.). However, the mosquito populations from Limbe and Buea were fully susceptible to malathion. The L1014F kdr was found in both An. coluzzii and An. gambiae (s.s.) with the highest frequencies found in An. gambiae (s.l.) populations from Tiko (94%) and Buea (90%) compared with the Limbe population (66%) (P = 0.00063, df = 2). No kdr L1014S was observed in analyzed samples.ConclusionsThese findings reemphasize the ongoing development of An. gambiae (s.l.) resistance to pyrethroids used in impregnating LLINs and suggest the use of malathion as an alternative insecticide for IRS in complementarity with LLINs.
Highlights
Members of the Anopheles gambiae (s.l.) complex are one of the major vectors of malaria in Africa
We report on the resistance of An. gambiae (s.s.) and An. coluzzii to deltamethrin, permethrin and their susceptibility to malathion in three areas of the South-West Region of Cameroon, four years after a countrywide distribution of Long-lasting insecticidal net (LLIN)
No KDT was recorded in contact with malathion insecticide since organophosphates are not characterized by a knockdown effect
Summary
Members of the Anopheles gambiae (s.l.) complex are one of the major vectors of malaria in Africa. LLINs and IRS are the most effective tools used in vector control of malaria Their effectiveness may be hampered by the development and spread of insecticide resistance in the target vectors species. Malaria remains the most important parasitic disease in the world, affecting mostly people in developing countries, especially in sub-Saharan Africa. The World Health Organization (WHO) has recently estimated that 840 million people are at risk from malaria, with most of them living in Africa where it is the leading cause of mortality [7]. Sub-Saharan Africa recorded 90% of the malaria mortality, representing a leading cause of deaths among children under 5 years old (70% of all deaths) [7]
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