Research
Pyrethroid resistance in the major malaria vector Anopheles arabiensis from Gwave, a malaria-endemic area in Zimbabwe
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* Corresponding author: Lizette K Koekemoer lizettek@nicd.ac.za
1 Department of Biological Sciences, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, Zimbabwe
2 Vector Control Reference Unit, National Institute for Communicable Diseases, NHLS, Private Bag X4, Sandringham, Johannesburg 2131, South Africa
3 School of Animal, Plant and Environmental Sciences, University of the Witwatersrand, Johannesburg, South Africa
4 Department of Public Health, P. Bag F26, Francistown, Botswana
5 Division of Virology and Communicable Diseases Surveillance, School of Pathology of the National Health Laboratory Service and the University of the Witwatersrand, Johannesburg, South Africa
Malaria Journal 2008, 7:247 doi:10.1186/1475-2875-7-247
Published: 28 November 2008Abstract
Background
Insecticide resistance can present a major obstacle to malaria control programmes. Following the recent detection of DDT resistance in Anopheles arabiensis in Gokwe, Zimbabwe, the underlying resistance mechanisms in this population were studied.
Methods
Standard WHO bioassays, using 0.75% permethrin, 4% DDT, 5% malathion, 0.1% bendiocarb and 4% dieldrin were performed on wild-collected adult anopheline mosquitoes and F1 progeny of An. arabiensis reared from wild-caught females. Molecular techniques were used for species identification as well as to identify knockdown resistance (kdr) and ace-1 mutations in individual mosquitoes. Biochemical assays were used to determine the relative levels of detoxifying enzyme systems including non-specific esterases, monooxygenases and glutathione-S-transferases as well as to detect the presence of an altered acetylcholine esterase (AChE).
Results
Anopheles arabiensis was the predominant member of the Anopheles gambiae complex. Of the 436 An. arabiensis females, 0.5% were positive for Plasmodium falciparum infection. WHO diagnostic tests on wild populations showed resistance to the pyrethroid insecticide permethrin at a mean mortality of 47% during February 2006 and a mean mortality of 68.2% in January 2008. DDT resistance (68.4% mean mortality) was present in February 2006; however, two years later the mean mortality was 96%. Insecticide susceptibility tests on F1 An. arabiensis families reared from material from two separate collections showed an average mean mortality of 87% (n = 758) after exposure to 4% DDT and 65% (n = 587) after exposure to 0.75% permethrin. Eight families were resistant to both DDT and permethrin. Biochemical analysis of F1 families reared from collections done in 2006 revealed high activity levels of monooxygenase (48.5% of families tested, n = 33, p < 0.05), glutathione S-transferase (25.8% of families tested, n = 31, p < 0.05) and general esterase activity compared to a reference susceptible An. arabiensis colony. Knockdown resistance (kdr) and ace-IR mutations were not detected.
Conclusion
This study confirmed the presence of permethrin resistance in An. arabiensis populations from Gwave and emphasizes the importance of periodic and ongoing insecticide susceptibility testing of malaria vector populations whose responses to insecticide exposure may undergo rapid change over time.