Liverpool School of Tropical Medicine, Pembroke Place, Liverpool L3 5QA, UK.
Malar J. 2012 Jan 23;11:24. doi: 10.1186/1475-2875-11-24.
The operational impact of insecticide resistance on the effectiveness of long-lasting insecticide nets (LLINs) and indoor residual spraying (IRS) is poorly understood. One factor which may prolong the effectiveness of these tools in the field is the increase in insecticide susceptibility with mosquito age. In this study, LLINs and IRS were tested against young (three to five days) and old (17-19 days) pyrethroid resistant Anopheles gambiae s.l. from Burkina Faso.
Blood-fed adult Anopheles gambiae s.l. were collected from south-west Burkina Faso and identified to species/form level. Cohorts of the F1 progeny of An. gambiae s.s. S-forms were exposed to deltamethrin (0.05%) at three to five or 17-19 days post-emergence and tested for the frequency of the resistance allele 1014F. Isofemale lines of the M, S- form of An. gambiae s.s. and Anopheles arabiensis were exposed in WHO cone tests to either a) LLINs deployed in households for two years or (b) bendiocarb sprayed walls.
Mortality rates in response to deltamethrin (0.05%) increased from levels indicative of strong resistance in three to five day old F1 mosquitoes, to near full susceptibility in the 17-19 day old cohort. On exposure to LLINs sampled from the field, the mortality rate in isofemale lines was higher in older mosquitoes than young (OR = 5.28, CI 95% = 2.81-9.92), although the mortality estimates were affected by the LLIN tested. In general, the LLINs sampled from the field performed poorly in WHO cone bioassays using either laboratory susceptible or field caught mosquito populations. Finally, there was a clear relationship between mortality and age on exposure to bendiocarb-sprayed walls, with older mosquitoes again proving more susceptible (OR = 3.39, CI 95% = 2.35-4.90).
Age is a key factor determining the susceptibility of mosquitoes to insecticides, not only in laboratory studies, but in response to field-based vector control interventions. This has important implications for understanding the epidemiological impact of resistance. If mosquitoes old enough to transmit malaria are still being suppressed with available insecticides, is resistance potentially having less of an impact than often assumed? However, the poor performance of LLINs used in this study in Burkina Faso, is a cause for concern and requires urgent investigation.
人们对杀虫剂抗性对长效杀虫剂蚊帐（LLINs）和室内滞留喷洒（IRS）效果的实际影响知之甚少。一个可能延长这些工具在田间效果的因素是，随着蚊子年龄的增长，杀虫剂敏感性增加。在这项研究中，对来自布基纳法索的对拟除虫菊酯具有抗性的年轻（三至五天）和年老（17-19 天）的疟蚊按蚊属进行了 LLINs 和 IRS 的测试。
从布基纳法索西南部收集吸食了血液的按蚊属疟蚊 s.l.，并按种/形态水平进行鉴定。来自 s.s. 形式的按蚊属疟蚊 F1 后代的蚊群在孵化后三至五天或 17-19 天暴露于氯菊酯（0.05%）下，并测试抗性等位基因 1014F 的频率。按蚊属疟蚊 s.s. 的 M、S 形态的同性别系和按蚊属 arabiensis 被暴露在 WHO 锥形测试中，要么接触在家庭中使用两年的 a）LLINs，要么接触 b）喷洒了双硫磷的墙壁。
三至五天龄 F1 蚊子对氯菊酯（0.05%）的死亡率表明存在强烈的抗性，而 17-19 天龄蚊群的死亡率接近完全敏感性。在接触从现场采集的 LLINs 时，较年长的蚊子的死亡率高于年轻蚊子（OR = 5.28，95%CI = 2.81-9.92），尽管死亡率估计受到测试的 LLINs 的影响。一般来说，从现场采集的 LLINs 在使用实验室敏感或现场捕获的蚊子种群进行的 WHO 锥形生物测定中表现不佳。最后，在接触喷洒了双硫磷的墙壁时，死亡率与年龄之间存在明显的关系，较年长的蚊子再次表现出更高的敏感性（OR = 3.39，95%CI = 2.35-4.90）。
年龄是决定蚊子对杀虫剂敏感性的关键因素，不仅在实验室研究中，而且在对基于现场的病媒控制干预措施的反应中都是如此。这对理解抗性的流行病学影响具有重要意义。如果足够老到可以传播疟疾的蚊子仍在被现有的杀虫剂抑制，那么抗性的影响是否比通常假设的要小？然而，在布基纳法索进行的这项研究中，LLINs 的表现不佳令人担忧，需要紧急调查。
