Division of Infectious Diseases, University of Alabama, Birmingham, Alabama 35294, USA.
Malar J. 2009 Nov 16;8:256. doi: 10.1186/1475-2875-8-256.
Insecticide-treated bed nets (ITNs), including long-lasting insecticidal nets (LLINs), play a primary role in global campaigns to roll back malaria in tropical Africa. Effectiveness of treated nets depends on direct impacts on individual mosquitoes including killing and excite-repellency, which vary considerably among vector species due to variations in host-seeking behaviours. While monitoring and evaluation programmes of ITNs have focuses on morbidity and all-cause mortality in humans, local entomological context receives little attention. Without knowing the dynamics of local vector species and their responses to treated nets, it is difficult to predict clinical outcomes when ITN applications are scaled up across African continent. Sound model frameworks incorporating intricate interactions between mosquitoes and treated nets are needed to develop the predictive capacity for scale-up applications of ITNs.
An established agent-based model was extended to incorporate the direct outcomes, e.g. killing and avoidance, of individual mosquitoes exposing to ITNs in a hypothetical village setting with 50 houses and 90 aquatic habitats. Individual mosquitoes were tracked throughout the life cycle across the landscape. Four levels of coverage, i.e. 40, 60, 80 and 100%, were applied at the household level with treated houses having only one bed net. By using Latin hypercube sampling scheme, parameters governing killing, diverting and personal protection of net users were evaluated for their relative roles in containing mosquito populations, entomological inoculation rates (EIRs) and malaria incidence.
There were substantial gaps in coverage between households and individual persons, and 100% household coverage resulted in circa 50% coverage of the population. The results show that applications of ITNs could give rise to varying impacts on population-level metrics depending on values of parameters governing interactions of mosquitoes and treated nets at the individual level. The most significant factor in determining effectiveness was killing capability of treated nets. Strong excito-repellent effect of impregnated nets might lead to higher risk exposure to non-bed net users.
With variabilities of vector mosquitoes in host-seeking behaviours and the responses to treated nets, it is anticipated that scale-up applications of INTs might produce varying degrees of success dependent on local entomological and epidemiological contexts. This study highlights that increased ITN coverage led to significant reduction in risk exposure and malaria incidence only when treated nets yielded high killing effects. It is necessary to test efficacy of treated nets on local dominant vector mosquitoes, at least in laboratory, for monitoring and evaluation of ITN programmes.
在非洲热带地区，经杀虫剂处理过的蚊帐（包括长效驱虫蚊帐）在遏制疟疾的全球运动中发挥着主要作用。处理过的蚊帐的有效性取决于对个体蚊子的直接影响，包括杀死和驱避，由于宿主寻找行为的变化，这些影响在不同的蚊子种类之间有很大的差异。虽然经杀虫剂处理的蚊帐的监测和评估方案侧重于人类的发病率和全因死亡率，但对当地昆虫学背景的关注甚少。如果不知道当地蚊子种类的动态及其对经杀虫剂处理的蚊帐的反应，那么当蚊帐在整个非洲大陆扩大应用时，就很难预测临床结果。需要有完善的模型框架，将蚊子与经杀虫剂处理的蚊帐之间的复杂相互作用纳入其中，以提高经杀虫剂处理的蚊帐扩大应用的预测能力。
在一个有 50 户房屋和 90 个水生栖息地的假设村庄环境中，将一个已建立的基于代理的模型进行扩展，以纳入个体蚊子暴露于经杀虫剂处理的蚊帐时的直接结果，如杀死和回避。个体蚊子在整个生命周期中在景观中被跟踪。在家庭层面上，以 40%、60%、80%和 100%的四个覆盖水平应用经杀虫剂处理的蚊帐，处理过的房屋只有一张床网。通过使用拉丁超立方抽样方案，评估了控制杀死、转向和蚊帐使用者个人保护的参数在控制蚊子种群、昆虫接种率（EIR）和疟疾发病率方面的相对作用。
家庭和个人之间的覆盖率存在很大差距，100%的家庭覆盖率导致约 50%的人口覆盖率。结果表明，经杀虫剂处理的蚊帐的应用可能会对人口水平指标产生不同的影响，这取决于个体层面上控制蚊子和经杀虫剂处理的蚊帐相互作用的参数值。决定有效性的最重要因素是处理过的蚊帐的杀灭能力。浸渍网的强烈兴奋驱避效应可能会导致非蚊帐使用者接触的风险增加。
由于媒介蚊子在宿主寻找行为和对经杀虫剂处理的蚊帐的反应方面存在变异性，预计经杀虫剂处理的蚊帐的扩大应用将根据当地的昆虫学和流行病学背景产生不同程度的成功。本研究强调，只有当处理过的蚊帐产生高杀灭效果时，增加经杀虫剂处理的蚊帐的覆盖率才能显著降低风险暴露和疟疾发病率。有必要在实验室中至少对当地主要媒介蚊子进行经杀虫剂处理的蚊帐的功效测试，以监测和评估经杀虫剂处理的蚊帐方案。
