Kristan M, Fleischmann H, della Torre A, Stich A, Curtis C F
Department of Infectious & Tropical Diseases, London School of Hygiene and Tropical Medicine, UK.
Med Vet Entomol. 2003 Sep;17(3):326-32. doi: 10.1046/j.1365-2915.2003.00449.x.
Resistance to pyrethroid insecticides and DDT caused by the kdr gene in the malaria vector Anopheles gambiae Giles s.s. (Diptera: Culicidae) has been reported in several West African countries. To test for pyrethroid resistance in two more countries, we sampled populations of the An. gambiae complex from south-western Ghana and from urban and rural localities in Ogun State, south-west Nigeria. Adult mosquitoes, reared from field-collected larvae, were exposed to the WHO-recommended discriminating dosage of exposure for 1 h to DDT 4%, deltamethrin 0.05% or permethrin 0.75% and mortality was recorded 24 h post-exposure. Susceptibility of An. gambiae s.l. to DDT was 94-100% in Ghana and 72-100% in Nigeria, indicating low levels of DDT resistance. Deltamethrin gave the highest mortality rates: 97-100% in Ghana, 95-100% in Nigeria. Ghanaian samples of An. gambiae s.l. were fully susceptible to permethrin, whereas some resistance to permethrin was detected at 4/5 Nigerian localities (percentage mortalities 75, 82, 88, 90 and 100%), with survivors including both An. arabiensis Patton and An. gambiae s.s. identified by PCR assay. Even so, the mean knockdown time was not significantly different from a susceptible reference strain, indicating absence or low frequency of kdr-type resistance. Such low levels of pyrethroid resistance are unlikely to impair the effectiveness of pyrethroid-impregnated bednets against malaria transmission. Among Nigerian samples of An. gambiae s.l., the majority from two urban localities were identified as An. arabiensis, whereas the majority from rural localities were An. gambiae s.s. These findings are consistent with those of M. Coluzzi et al. (1979). Differences of ecological distribution between molecular forms of An. gambiae s.s. were also found, with rural samples almost exclusively of the S-form, whereas the M-form predominated in urban samples. It is suggested that 'urban island' populations of An. arabiensis and of An. gambiae s.s. M-form in the rainforest belt of West Africa might be appropriate targets for elimination of these malaria vectors by the sterile insect technique.
在几个西非国家，已报道冈比亚按蚊（双翅目：蚊科）中因kdr基因导致对拟除虫菊酯类杀虫剂和滴滴涕产生抗性。为了在另外两个国家检测拟除虫菊酯抗性，我们从加纳西南部以及尼日利亚西南部奥贡州的城市和农村地区采集了冈比亚按蚊复合体种群样本。将野外采集的幼虫饲养出的成年蚊子暴露于世界卫生组织推荐的鉴别剂量的4%滴滴涕、0.05%溴氰菊酯或0.75%氯菊酯中1小时，并在暴露后24小时记录死亡率。在加纳，冈比亚按蚊复合种群对滴滴涕的易感性为94% - 100%，在尼日利亚为72% - 100%，表明滴滴涕抗性水平较低。溴氰菊酯的死亡率最高：在加纳为97% - 100%，在尼日利亚为95% - 100%。加纳的冈比亚按蚊复合种群样本对氯菊酯完全敏感，而在尼日利亚的5个地区中有4个检测到对氯菊酯有一定抗性（死亡率分别为75%、82%、88%、90%和100%），通过PCR检测确定存活者包括阿拉伯按蚊和冈比亚按蚊。即便如此，平均击倒时间与敏感参照品系无显著差异，表明不存在kdr型抗性或其频率较低。如此低水平的拟除虫菊酯抗性不太可能削弱拟除虫菊酯浸渍蚊帐对疟疾传播的防控效果。在尼日利亚的冈比亚按蚊复合种群样本中，来自两个城市地区的大多数被鉴定为阿拉伯按蚊，而来自农村地区的大多数是冈比亚按蚊。这些发现与M. 科卢齐等人（1979年）的结果一致。还发现了冈比亚按蚊不同分子型在生态分布上存在差异，农村样本几乎全是S型，而城市样本中M型占主导。有人提出，西非雨林带中阿拉伯按蚊和冈比亚按蚊M型的“城市岛屿”种群可能是通过昆虫不育技术消除这些疟疾传播媒介的合适目标。
