Department of Disease Control, London School of Hygiene and Tropical Medicine, Keppel Street, London, UK.
Malar J. 2013 May 2;12:149. doi: 10.1186/1475-2875-12-149.
To control malaria in Tanzania, two primary vector control interventions are being scaled up: long-lasting insecticide-treated nets (LLINs) and indoor residual spraying (IRS). The main threat to effective malaria control is the selection of insecticide resistance. While resistance to pyrethroids, the primary insecticide used for LLINs and IRS, has been reported among mosquito vectors in only a few sites in Tanzania, neighbouring East African countries are recording increasing levels of resistance. To monitor the rapidly evolving situation, the resistance status of the malaria vector Anopheles gambiae s.l to different insecticides and the prevalence of the kdr resistance allele involved in pyrethroid resistance were investigated in north-western Tanzania, an area that has been subject to several rounds of pyrethroid IRS since 2006.
Household collections of anopheline mosquitoes were exposed to diagnostic dosages of pyrethroid, DDT, and bendiocarb using WHO resistance test kits. The relative proportions of An. gambiae s.s and Anopheles arabiensis were also investigated among mosquitoes sampled using indoor CDC light traps. Anophelines were identified to species and the kdr mutation was detected using real time PCR TaqMan assays.
From the light trap collections 80% of An. gambiae s.l were identified as An. gambiae s.s and 20% as An. arabiensis. There was cross-resistance between pyrethroids and DDT with mortality no higher than 40% reported in any of the resistance tests. The kdr-eastern variant was present in homozygous form in 97% of An. gambiae s.s but was absent in An. arabiensis. Anopheles gambiae s.s showed reduced susceptibility to the carbamate insecticide, bendiocarb, the proportion surviving WHO tests ranging from 0% to 30% depending on season and location.
Anopheles gambiae s.s has developed phenotypic resistance to pyrethroids and DDT and kdr frequency has almost reached fixation. Unlike in coastal Tanzania, where the ratio of An. gambiae s.s to An. arabiensis has decreased in response to vector control, An. gambiae s.s persists at high frequency in north-western Tanzania, probably due to selection of pyrethroid resistance, and this trend is likely to arise in other areas as resistance spreads or is subject to local selection from IRS or LLINs.
为了在坦桑尼亚控制疟疾，正在扩大两项主要的病媒控制干预措施：长效驱虫蚊帐（LLIN）和室内滞留喷洒（IRS）。有效疟疾控制的主要威胁是杀虫剂耐药性的选择。虽然在坦桑尼亚的少数几个地点已经报告了蚊子传播媒介对拟除虫菊酯类杀虫剂的耐药性，但东非邻国的耐药性水平正在上升。为了监测迅速变化的情况，在坦桑尼亚西北部，对疟疾传播媒介冈比亚按蚊（Anopheles gambiae s.l.）对不同杀虫剂的抗药性状况以及参与拟除虫菊酯类杀虫剂抗药性的 kdr 抗性等位基因的流行情况进行了调查。该地区自 2006 年以来已经进行了几轮拟除虫菊酯 IRS。
使用世界卫生组织（WHO）抗药性测试试剂盒，对家庭收集的按蚊进行了诊断剂量的拟除虫菊酯、DDT 和苯氧威的暴露试验。还使用室内 CDC 诱蚊灯对采集的蚊子进行了按蚊 gambiae s.s 和安蚊（Anopheles arabiensis）相对比例的调查。对按蚊进行了种属鉴定，并使用实时 PCR TaqMan 法检测了 kdr 突变。
从诱蚊灯收集的按蚊中，80%的 An. gambiae s.l.被鉴定为 An. gambiae s.s，20%为 An. arabiensis。拟除虫菊酯类和 DDT 之间存在交叉耐药性，任何抗药性测试的死亡率均不超过 40%。kdr-东部变体以纯合形式存在于 97%的 An. gambiae s.s 中，但在 An. arabiensis 中不存在。安蚊 gambiae s.s 对氨基甲酸酯类杀虫剂苯氧威的敏感性降低，世界卫生组织测试中存活的比例因季节和地点而异，从 0%到 30%不等。
冈比亚按蚊已对拟除虫菊酯类和 DDT 产生表型抗药性，kdr 频率几乎达到固定水平。与沿海坦桑尼亚不同，在那里，由于病媒控制，安蚊 gambiae s.s 与安蚊（An. arabiensis）的比例有所下降，在西北部的坦桑尼亚，安蚊 gambiae s.s 仍然高频存在，这可能是由于对拟除虫菊酯类杀虫剂的选择，随着抗药性的传播或 IRS 或 LLINs 的局部选择，这种趋势可能会在其他地区出现。
