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Anti-malaria interventions that rely on insecticides can be compromised by insecticide-resistance alleles among malaria vectors. We examined frequency changes of resistance alleles at two loci, knockdown resistance (kdr) and acetylcholinesterase-1 (ace-1), which confer resistance to pyrethroids and DDT, and carbamates, respectively. A total of 7,059 Anopheles gambiae sensu stricto mosquitoes were analyzed from multiple sites across continental Equatorial Guinea. A subset of sites included samples collected pre-intervention (2007) and post-intervention (2009–2011). Both L1014S and L1014F resistance alleles were observed in almost all pre-intervention collections. In particular, L1014F was already at substantial frequencies in M form populations (17.6–74.6%), and at high frequencies (> 50%) in all but two S form populations. Comparison before and throughout anti-vector interventions showed drastic increases in L1014F, presumably caused by intensified selection pressure imposed by pyrethroids used in vector control efforts. In light of these findings, inclusion of other insecticide classes in any anti-vector intervention can be considered prudent.
Author contributions: Michael R. Reddy conceived and planned the study, performed a portion of the pre-intervention collections, supervised the molecular analyses of all specimens, and composed the first draft of the manuscript; Adrian Godoy, performed molecular analyses of collected specimens and contributed to manuscript preparation; Kirstin Dion, supervised and performed molecular analyses and contributed to manuscript preparation; Abrahan Matias, coordinated and supervised the 2009–2011 field collections; Kevin Callender contributed statistical analysis assistance; Anthony E. Kiszewski participated in the study design, provided statistical analysis assistance and editorial input, and contributed to manuscript preparation; Immo Kleinschmidt designed the pre-intervention window trap monitoring system and facilitated the use of archived mosquito samples collected before initiation of intervention activities; Frances C. Ridl processed and archived mosquitoes collected during the pre-intervention period and assisted in the transfer of these specimens to the Yale laboratory for further molecular analysis; Jeffrey R. Powell planned and supervised the study and assisted in analysis of results; Adalgisa Caccone planned and supervised the study, assisted in analysis of results, and contributed to manuscript preparation; and Michel A. Slotman planned and supervised the study, assisted in analysis of results, and co-wrote the manuscript.
Financial support: This study was supported by an operational research grant awarded by the Bioko Island Malaria Control Program to Michael A. Slotman and Adalgisa Caccone. The Bioko Island Malaria Control Program is supported by a consortium led by Marathon Oil Corporation (Houston, TX) and the government of Equatorial Guinea. This study was also supported by EGMCI, which was supported through a grant from the Global Fund to Fight AIDS, Tuberculosis and Malaria.
Authors' addresses: Michael R. Reddy, Department of Epidemiology and Public Health, Yale University, New Haven CT, E-mail: email@example.com. Adrian Godoy, Kirstin Dion, Jeffrey R. Powell, and Adalgisa Caccone, Department of Ecology and Evolutionary Biology, Yale University, New Haven CT, E-mails: firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, and email@example.com. Abrahan Matias, Medical Care Development International Inc., Silver Spring, MD, E-mail: firstname.lastname@example.org. Kevin Callender, Department of Psychology, Yale University, New Haven, CT, E-mail: email@example.com. Anthony E. Kiszewski, Department of Natural and Applied Sciences, Bentley University, Waltham, MA, E-mail: firstname.lastname@example.org. Immo Kleinschmidt, Medical Research Council Topical Epidemiology Group, London School of Hygiene and Tropical Medicine, London, UK, E-mail: email@example.com. Frances C. Ridl, Malaria Research Lead Programme, Medical Research Council, Durban, South Africa, E-mail: firstname.lastname@example.org. Michel A. Slotman, Department of Entomology, Texas A&M University, College Station, TX, E-mail: email@example.com.