BACKGROUND The efficacy of long-lasting insecticidal nets (LLINs) in preventing malaria in Africa is threatened by insecticide resistance. Bioassays assessing 24-hour mortality post-LLIN exposure have established that resistance to the concentration of pyrethroids used in LLINs is widespread. However, although mosquitoes may no longer be rapidly killed by LLIN exposure, a delayed mortality effect has been shown to reduce the transmission potential of mosquitoes exposed to nets. This has been postulated to partially explain the continued efficacy of LLINs against pyrethroid-resistant populations. Burkina Faso is one of a number of countries with very high malaria burdens and pyrethroid-resistant vectors, where progress in controlling this disease has stagnated. We measured the impact of LLIN exposure on mosquito longevity in an area of the country with intense pyrethroid resistance to establish whether pyrethroid exposure was still shortening mosquito lifespan in this setting. METHODS We quantified the immediate and delayed mortality effects of LLIN exposure using standard laboratory WHO cone tests, tube bioassays and experimental hut trials on Anopheles gambiae populations originating from the Cascades region of Burkina Faso using survival analysis and a Bayesian state-space model. RESULTS Following single and multiple exposures to a PermaNet 2.0 LLIN only one of the four mosquito populations tested showed evidence of delayed mortality. No delayed mortality was seen in experimental hut studies using LLINs. A delayed mortality effect was only observed in WHO tube bioassays when deltamethrin concentration was increased above the standard diagnostic dose. CONCLUSIONS As mosquito pyrethroid-resistance increases in intensity, delayed effects from LLIN exposure are substantially reduced or absent. Given the rapid increase in resistance occurring in malaria vectors across Africa it is important to determine whether the failure of LLINs to shorten mosquito lifespan is now a widespread phenomenon as this will have important implications for the future of this pivotal malaria control tool.

中文翻译：

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来自布基纳法索的冈比亚按蚊种群在接触杀虫剂处理的蚊帐后表现出最小的延迟死亡率。

背景技术长效杀虫蚊帐 (LLIN) 在非洲预防疟疾方面的功效受到杀虫剂耐药性的威胁。评估 LLIN 暴露后 24 小时死亡率的生物测定表明，对 LLIN 中使用的拟除虫菊酯浓度的抗性很普遍。然而，尽管蚊子可能不再被 LLIN 暴露迅速杀死，但已显示延迟死亡率效应会降低蚊子暴露于蚊帐的传播潜力。这被假定为部分解释了 LLIN 对拟除虫菊酯抗性人群的持续功效。布基纳法索是疟疾负担非常高且病媒对拟除虫菊酯具有抗药性的众多国家之一，这些国家在控制这种疾病方面的进展停滞不前。我们测量了在该国具有强烈拟除虫菊酯抗性的地区，LLIN 暴露对蚊子寿命的影响，以确定在这种情况下，拟除虫菊酯暴露是否仍在缩短蚊子的寿命。方法 我们使用生存分析和贝叶斯状态空间模型，对源自布基纳法索喀斯喀特地区的冈比亚按蚊种群进行标准实验室 WHO 锥体测试、试管生物测定和实验性小屋试验，量化 LLIN 暴露的直接和延迟死亡率影响。结果 在单次和多次暴露于 PermaNet 2.0 LLIN 之后，测试的四个蚊子种群中只有一个显示出延迟死亡的证据。在使用 LLIN 的实验性小屋研究中没有发现延迟死亡率。仅当溴氰菊酯浓度增加到标准诊断剂量以上时，才在 WHO 试管生物测定中观察到延迟死亡效应。结论随着蚊子对拟除虫菊酯的抗性强度增加，LLIN 暴露的延迟效应显着降低或不存在。鉴于整个非洲疟疾病媒的耐药性迅速增加，重要的是要确定 LLIN 未能缩短蚊子寿命现在是否是一种普遍现象，因为这将对这一关键疟疾控制工具的未来产生重要影响。