Department of Vector Ecology and Environment, Institute of Tropical Medicine, Nagasaki University, Nagasaki, Japan.
PLoS One. 2011;6(8):e22574. doi: 10.1371/journal.pone.0022574. Epub 2011 Aug 11.
Anopheles gambiae s.s., Anopheles arabiensis, and Anopheles funestus s.s. are the most important species for malaria transmission. Pyrethroid resistance of these vector mosquitoes is one of the main obstacles against effective vector control. The objective of the present study was to monitor the pyrethroid susceptibility in the 3 major malaria vectors in a highly malaria endemic area in western Kenya and to elucidate the mechanisms of pyrethroid resistance in these species. Gembe East and West, Mbita Division, and 4 main western islands in the Suba district of the Nyanza province in western Kenya were used as the study area. Larval and adult collection and bioassay were conducted, as well as the detection of point mutation in the voltage-gated sodium channel (1014L) by using direct DNA sequencing. A high level of pyrethroid resistance caused by the high frequency of point mutations (L1014S) was detected in An. gambiae s.s. In contrast, P450-related pyrethroid resistance seemed to be widespread in both An. arabiensis and An. funestus s.s. Not a single L1014S mutation was detected in these 2 species. A lack of cross-resistance between DDT and permethrin was also found in An. arabiensis and An. funestus s.s., while An. gambiae s.s. was resistant to both insecticides. It is noteworthy that the above species in the same area are found to be resistant to pyrethroids by their unique resistance mechanisms. Furthermore, it is interesting that 2 different resistance mechanisms have developed in the 2 sibling species in the same area individually. The cross resistance between permethrin and DDT in An. gambiae s.s. may be attributed to the high frequency of kdr mutation, which might be selected by the frequent exposure to ITNs. Similarly, the metabolic pyrethroid resistance in An. arabiensis and An. funestus s.s. is thought to develop without strong selection by DDT.
冈比亚按蚊、阿拉伯按蚊和致倦库蚊是最重要的疟疾传播媒介。这些媒介蚊虫对拟除虫菊酯的抗药性是有效控制媒介的主要障碍之一。本研究的目的是监测肯尼亚西部高度疟疾流行地区的 3 种主要疟疾媒介对拟除虫菊酯的敏感性，并阐明这些物种对拟除虫菊酯的抗药性机制。研究区域为肯尼亚西部尼扬扎省苏巴区 Mbita 分区的 Gembe 东和西以及 4 个主要的西部岛屿。进行了幼虫和成虫采集和生物测定，以及通过直接 DNA 测序检测电压门控钠离子通道（1014L）中的点突变。冈比亚按蚊中检测到高水平的拟除虫菊酯抗性，这是由于点突变（L1014S）的高频所致。相比之下，在阿拉伯按蚊和致倦库蚊中似乎广泛存在与 P450 相关的拟除虫菊酯抗性。在这 2 个物种中均未检测到 L1014S 突变。还发现阿拉伯按蚊和致倦库蚊对滴滴涕和溴氰菊酯之间缺乏交叉抗性，而冈比亚按蚊对这两种杀虫剂均有抗性。值得注意的是，同一地区的上述物种通过其独特的抗性机制被发现对拟除虫菊酯具有抗性。此外，有趣的是，同一地区的 2 个亲缘物种各自发展出了 2 种不同的抗性机制。冈比亚按蚊中溴氰菊酯和滴滴涕之间的交叉抗性可能归因于 kdr 突变的高频发生，这可能是由频繁接触 ITN 选择所致。同样，阿拉伯按蚊和致倦库蚊中的代谢性拟除虫菊酯抗性被认为是在没有滴滴涕强烈选择的情况下发展起来的。
