MRC Centre for Outbreak Analysis & Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London, England.
PLoS Med. 2010 Aug 10;7(8):e1000324. doi: 10.1371/journal.pmed.1000324.
Over the past decade malaria intervention coverage has been scaled up across Africa. However, it remains unclear what overall reduction in transmission is achievable using currently available tools.
We developed an individual-based simulation model for Plasmodium falciparum transmission in an African context incorporating the three major vector species (Anopheles gambiae s.s., An. arabiensis, and An. funestus) with parameters obtained by fitting to parasite prevalence data from 34 transmission settings across Africa. We incorporated the effect of the switch to artemisinin-combination therapy (ACT) and increasing coverage of long-lasting insecticide treated nets (LLINs) from the year 2000 onwards. We then explored the impact on transmission of continued roll-out of LLINs, additional rounds of indoor residual spraying (IRS), mass screening and treatment (MSAT), and a future RTS,S/AS01 vaccine in six representative settings with varying transmission intensity (as summarized by the annual entomological inoculation rate, EIR: 1 setting with low, 3 with moderate, and 2 with high EIRs), vector-species combinations, and patterns of seasonality. In all settings we considered a realistic target of 80% coverage of interventions. In the low-transmission setting (EIR approximately 3 ibppy [infectious bites per person per year]), LLINs have the potential to reduce malaria transmission to low levels (<1% parasite prevalence in all age-groups) provided usage levels are high and sustained. In two of the moderate-transmission settings (EIR approximately 43 and 81 ibppy), additional rounds of IRS with DDT coupled with MSAT could drive parasite prevalence below a 1% threshold. However, in the third (EIR = 46) with An. arabiensis prevailing, these interventions are insufficient to reach this threshold. In both high-transmission settings (EIR approximately 586 and 675 ibppy), either unrealistically high coverage levels (>90%) or novel tools and/or substantial social improvements will be required, although considerable reductions in prevalence can be achieved with existing tools and realistic coverage levels.
Interventions using current tools can result in major reductions in P. falciparum malaria transmission and the associated disease burden in Africa. Reduction to the 1% parasite prevalence threshold is possible in low- to moderate-transmission settings when vectors are primarily endophilic (indoor-resting), provided a comprehensive and sustained intervention program is achieved through roll-out of interventions. In high-transmission settings and those in which vectors are mainly exophilic (outdoor-resting), additional new tools that target exophagic (outdoor-biting), exophilic, and partly zoophagic mosquitoes will be required.
在过去的十年中，疟疾干预措施的覆盖范围在非洲得到了扩大。然而，目前尚不清楚利用现有的工具可以实现多大程度的传播总体减少。
我们开发了一种基于个体的模拟模型，用于在非洲背景下传播疟原虫，该模型结合了三种主要的蚊子物种（冈比亚按蚊 s.s.、阿拉伯按蚊和芬斯顿按蚊），并使用从非洲 34 个传播环境中获得的寄生虫流行数据进行拟合。我们纳入了从 2000 年开始使用青蒿素联合疗法（ACT）和增加长效驱虫蚊帐（LLIN）覆盖率的影响。然后，我们在六个具有不同传播强度（以每年的昆虫接种率 EIR 来概括：1 个低强度、3 个中强度和 2 个高强度设置）、蚊子物种组合和季节性模式的代表性环境中，探索了继续推出 LLIN、额外的室内滞留喷洒（IRS）、大规模筛查和治疗（MSAT）以及未来 RTS,S/AS01 疫苗对传播的影响。在所有环境中，我们都考虑了干预措施 80%的覆盖率这一现实目标。在低传播环境（EIR 约为 3 ibppy[每年每人感染性叮咬次数]）中，如果使用水平高且持续，LLIN 有可能将疟疾传播降低到低水平（所有年龄组的寄生虫流行率均低于 1%）。在两个中度传播环境（EIR 约为 43 和 81 ibppy）中，使用滴滴涕进行额外的 IRS 与 MSAT 结合可以将寄生虫流行率降低到 1%以下的阈值。然而，在第三个（EIR=46）以阿拉伯按蚊为主的环境中，这些干预措施不足以达到这一阈值。在两个高强度传播环境（EIR 约为 586 和 675 ibppy）中，要么需要不切实际的高覆盖率（>90%），要么需要新的工具和/或实质性的社会改善，尽管通过现有工具和现实的覆盖率水平可以实现患病率的显著降低。
使用现有工具的干预措施可以大大降低非洲间日疟的传播和相关疾病负担。在以嗜内（室内休息）为主的蚊子的低至中度传播环境中，当实现综合和持续的干预计划时，将传播率降低到 1%的寄生虫流行率阈值是可能的。在高度传播的环境中，以及在以嗜外（室外休息）为主的环境中，将需要新的工具，这些工具将针对嗜外（室外叮咬）、嗜外和部分食虫性蚊子。
