Munhenga Givemore, Masendu Hieronymo T, Brooke Basil D, Hunt Richard H, Koekemoer Lizette K
Department of Biological Sciences, University of Zimbabwe, Mount Pleasant, Harare, Zimbabwe.
Malar J. 2008 Nov 28;7:247. doi: 10.1186/1475-2875-7-247.
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.
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).
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.
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.
杀虫剂抗性可能成为疟疾控制项目的主要障碍。在津巴布韦戈奎地区近期检测到阿拉伯按蚊对滴滴涕产生抗性后，对该种群潜在的抗性机制进行了研究。
使用0.75%氯菊酯、4%滴滴涕、5%马拉硫磷、0.1%残杀威和4%狄氏剂进行标准的世卫组织生物测定，对野外采集的成年按蚊和从野外捕获的雌性按蚊饲养的阿拉伯按蚊F1代进行检测。分子技术用于物种鉴定以及识别个体蚊子中的击倒抗性（kdr）和ace-1突变。生化测定用于确定解毒酶系统的相对水平，包括非特异性酯酶、单加氧酶和谷胱甘肽-S-转移酶，以及检测是否存在改变的乙酰胆碱酯酶（AChE）。
阿拉伯按蚊是冈比亚按蚊复合体的主要成员。在436只阿拉伯按蚊雌性中，0.5%的恶性疟原虫感染呈阳性。对野生种群的世卫组织诊断测试显示，2006年2月对拟除虫菊酯类杀虫剂氯菊酯产生抗性，平均死亡率为47%，2008年1月平均死亡率为68.2%。2006年2月存在滴滴涕抗性（平均死亡率68.4%）；然而，两年后平均死亡率为96%。对从两个不同采集点采集的材料饲养的阿拉伯按蚊F1代进行杀虫剂敏感性测试，暴露于4%滴滴涕后平均死亡率为87%（n = 758），暴露于0.75%氯菊酯后平均死亡率为65%（n = 587）。有8个家系对滴滴涕和氯菊酯均有抗性。对2006年采集的样本饲养的F1代家系进行生化分析，与参考易感阿拉伯按蚊群体相比，单加氧酶（测试家系的48.5%，n = 33, p < 0.05）、谷胱甘肽S-转移酶（测试家系的25.8%，n = 31, p < 0.05）和一般酯酶活性水平较高。未检测到击倒抗性（kdr）和ace-IR突变。
本研究证实了戈奎地区阿拉伯按蚊种群中存在氯菊酯抗性，并强调了对疟疾媒介种群进行定期和持续杀虫剂敏感性测试的重要性，因为这些种群对杀虫剂暴露的反应可能会随时间迅速变化。
