MRC Centre for Global Infectious Disease Analysis, School of Public Health, Imperial College London, London, UK.
London Centre for Neglected Tropical Disease Research, Department of Infectious Disease Epidemiology, Imperial College London, London, UK.
J R Soc Interface. 2021 Apr;18(177):20210200. doi: 10.1098/rsif.2021.0200. Epub 2021 Apr 28.
The existence of multiple stable equilibria in models of parasitic helminth transmission was a ground-breaking discovery over 30 years ago. An implication of this discovery, that there is a level of infection below which transmission cannot self-sustain called the transmission breakpoint, has in part motivated the push towards the elimination of many human diseases caused by the multiple species of helminth worldwide. In the absence of vaccines, the predominant method in this push towards elimination is to repeatedly administer endemic populations with anthelmintic drugs, over several treatment rounds, in what has become to be known as mass drug administration (MDA). MDA will inevitably alter the distribution of parasite burdens among hosts from the baseline distribution, and significantly, the location of the transmission breakpoint is known to be dependent on the level of aggregation of this distribution-for a given mean worm burden, more highly aggregated distributions where fewer individuals harbour most of the burden, will have a lower transmission breakpoint. In this paper, we employ a probabilistic analysis of the changes to the distribution of burdens in a population undergoing MDA, and simple approximations, to determine how key aspects of the programmes (including compliance, drug efficacy and treatment coverage) affect the location of the transmission breakpoint. We find that individual compliance to treatment, which determines the number of times an individual participates in mass drug administration programmes, is key to the location of the breakpoint, indicating the vital importance to ensure that people are not routinely missed in these programmes.
三十多年前，人们在寄生虫蠕虫传播模型中发现了多个稳定平衡点的存在，这是一个开创性的发现。这一发现的一个含义是，存在一个感染水平，低于该水平传播就无法自我维持，这被称为传播断点。这在一定程度上推动了消除全球多种由蠕虫引起的人类疾病的努力。在没有疫苗的情况下，消除工作的主要方法是通过多次治疗轮次，反复向流行地区的人群施用驱虫药物，这已成为众所周知的大规模药物治疗（MDA）。MDA 不可避免地会改变宿主之间寄生虫负担的分布，从基线分布开始改变，而重要的是，已知传播断点的位置取决于这种分布的聚集程度——对于给定的平均蠕虫负担，负担集中在少数个体上的高度聚集分布，将具有更低的传播断点。在本文中，我们采用对正在接受 MDA 的人群中负担分布变化的概率分析，并采用简单的近似方法，来确定方案的关键方面（包括依从性、药物疗效和治疗覆盖率）如何影响传播断点的位置。我们发现，个体对治疗的依从性，即一个人参与大规模药物治疗方案的次数，是决定断点位置的关键因素，这表明确保人们不会在这些方案中被常规遗漏至关重要。
