Betson Martha, Jawara Musa, Awolola Taiwo Samson
Department of Infectious and Tropical Diseases, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.
Malar J. 2009 Aug 5;8:187. doi: 10.1186/1475-2875-8-187.
Vector control is an effective way of reducing malaria transmission. The main vector control methods include the use of insecticide-treated bed nets and indoor residual spraying (IRS). Both interventions rely on the continuing susceptibility of Anopheles to a limited number of insecticides. However, insecticide resistance, in particular pyrethroid-DDT cross-resistance, is a challenge facing malaria vector control in Africa because pyrethroids represent the only class of insecticides approved for treating bed nets and DDT is commonly used for IRS. Here baseline data are presented on the insecticide susceptibility levels of malaria vectors prior to The Gambian indoor residual spraying intervention programme.
Anopheles larvae were collected from six malaria surveillance sites (Brikama, Essau, Farafenni, Mansakonko, Kuntaur and Basse) established by the National Malaria Control Programme and the UK Medical Research Council Laboratories in The Gambia. The mosquitoes were reared to adulthood and identified using morphological keys and a species-specific polymerase chain reaction assay. Two- to three-day old adult female mosquitoes were tested for susceptibility to permethrin, deltamethrin and DDT using standard WHO protocols, insecticide susceptibility test kits and treated papers.
All Anopheles mosquitoes tested belonged to the Anopheles gambiae complex. Anopheles arabiensis was predominant (54.1%), followed by An. gambiae s.s. (26.1%) and Anopheles melas (19.8%). Anopheles gambiae s.s. and An. arabiensis were found at all six sites. Anopheles melas was recorded only at Brikama. Mosquitoes from two of the six sites (Brikama and Basse) were fully susceptible to all three insecticides tested. However, DDT resistance was found in An. gambiae from Essau where the 24 hours post-exposure mortality was <80% but 88% for permethrin and 92% for deltamethrin.
This current survey of insecticide resistance in Anopheles provides baseline information for monitoring resistance in The Gambia and highlights the need for routine resistance surveillance as an integral part of the proposed nation wide IRS intervention using DDT.
病媒控制是减少疟疾传播的有效方法。主要的病媒控制方法包括使用经杀虫剂处理的蚊帐和室内滞留喷洒（IRS）。这两种干预措施都依赖于按蚊对有限数量杀虫剂的持续易感性。然而，杀虫剂抗性，特别是拟除虫菊酯 - DDT交叉抗性，是非洲疟疾病媒控制面临的一项挑战，因为拟除虫菊酯是唯一被批准用于处理蚊帐的一类杀虫剂，而DDT常用于室内滞留喷洒。本文呈现了冈比亚室内滞留喷洒干预计划实施前疟疾病媒的杀虫剂敏感性水平的基线数据。
按蚊幼虫从冈比亚国家疟疾控制计划和英国医学研究理事会实验室设立的六个疟疾监测点（布里卡马、埃绍、法拉芬尼、曼萨孔科、昆陶尔和巴塞）采集。将蚊子饲养至成年，并使用形态学特征和物种特异性聚合酶链反应测定法进行鉴定。使用标准的世卫组织规程、杀虫剂敏感性测试试剂盒和处理过的纸片，对2至3日龄的成年雌蚊进行对氯菊酯、溴氰菊酯和DDT的敏感性测试。
所有测试的按蚊均属于冈比亚按蚊复合体。阿拉伯按蚊占主导（54.1%），其次是冈比亚按蚊指名亚种（26.1%）和梅拉斯按蚊（19.8%）。在所有六个监测点均发现了冈比亚按蚊指名亚种和阿拉伯按蚊。仅在布里卡马记录到梅拉斯按蚊。六个监测点中的两个（布里卡马和巴塞）的蚊子对所有三种测试杀虫剂均完全敏感。然而，在埃绍的冈比亚按蚊中发现了对DDT的抗性，暴露后24小时的死亡率<80%，但对氯菊酯为88%，对溴氰菊酯为92%。
本次按蚊杀虫剂抗性调查为冈比亚监测抗性提供了基线信息，并强调了将常规抗性监测作为拟议的全国范围内使用DDT进行室内滞留喷洒干预的一个组成部分的必要性。
