Precision Mapping-Tackling a major obstacle on the road towards the elimination of schistosomiasis

Schistosomiasis affects over 200 million people, yet it is a highly focal disease, with the likelihood of re-infection necessitating regular treatment of at-risk populations. Mapping methods that do not take into account the focal nature of it's distribution can lead to at-risk communities not being treated or over-treating communities that do not need it. This causes several issues, from wasted medicines and resources to treatment fatigue and non-compliance (where communities refuse to take donated medicines). The answer could be a refined, higher resolution, dynamic mapping system, i.e. Precision mapping!

血吸虫病的背景

血吸虫病,此病也叫做裂体血吸虫,是一个标准asitic disease caused by worms. Infection usually occurs when individuals are exposed to infested water. Thus, high levels of schistosomiasis infections occur where there is a high interaction between people, worms and water. It can therefore be said that schistosomiasis is a focal disease.

Life cycle of S. mansoni. Copyright Trustees of the Natural History Museum

曾经的血吸虫病的幼虫形式进入了成人棘突中的血液。对于大多数情况下,在寄生疾病中,雌性形式引起了杀手的打击。一旦成熟并与男性的雌性血吸虫释放出卵,其中一些通过排泄物从体内传递出来,以将寄生虫的生命周期延续到附近的水源中,可能包含中间宿主蜗牛。其他人被困在身体组织中,导致免疫反应和逐渐损伤。

症状以及导致与血吸虫病相关的继发性疾病的慢性炎症和免疫力损害可能会造成灾难性,并可能对某个地区的身体和经济健康产生毁灭性的影响。

血吸虫病是一种贫困疾病,由于缺乏清洁的水供应,人们常常被迫使用相同的水进行职业,农业,家庭和娱乐活动。由于水的身体展现了一个完美的游乐区,因此学龄儿童特别容易受到感染。我的意思是,谁不想在放学后的炎热的一天不想去游泳和钓鱼?

How Schistosomiasis is currently controlled

血吸虫病以几种不同的方式控制。通过水卫生和卫生(WASH)实践,蜗牛控制和最后一次,但绝非最不重要的,定期的大规模人口治疗,通常在几年内进行。在2016年20640万人需要预防化疗(PC). (Nothing to do with cancer, chemo meaning chemical. So, therapy with chemicals, I know it’s confusing).

School-children receiving Praziquantel and albendazole treatment – image copyright Steffi Knopp

How Schistosomiasis is currently mapped

Mapping is a critical step in understanding where at-risk populations live in order to target them effectively. For schistosomiasis, the initial mapping is done by collecting stool and/or urine samples in a sub-sample of five schools per health district, 50 children per school are selected for parasitological surveys. The eligibility of the district for PC is then determined by the mean prevalence that allows the entire district to be classified as nonendemic (Tchuem Tchuenté et al., 2017)。

This is a map of the African continent showing the level of chistosomiasis endiemicity in different areas of endemic countries. Copyright WHO
Schistosomiasis endemicty map from WHO AFRO Expanded Special Project for the Elimination of Neglected Tropical Diseases (ESPEN)
Schistosomiasis endemicty map from WHO AFRO Expanded Special Project for the Elimination of Neglected Tropical Diseases (ESPEN)

The problem with averages

使用平均值具有其局限性,这是因为每当使用平均值来表示不确定数量时,结果就会扭曲,因为不可避免的变化的影响将被忽略。((Savage, 2002)。

血吸虫病的焦点及其对各种生态和流行病学因素的依赖性的性质意味着在同一健康区内的子堵塞和学校之间存在显着差异。’只有少数学校来决定整个地区的地方性,如果无法正确进行现场选择和抽样,则会导致一些不确定性和错误”(Tchuenté et al., 2018)。这导致围绕哪些地区有资格获得预防化疗(PC)的歧义,这阻碍了人口的成功有效报告和覆盖范围。

因此,这就是问题,解决方案呢?好吧,从数学上讲,使用分布分布 - 一系列相关值,而不是单个值更有用,因为它使资源经理能够捕获一个区域的更高分辨率快照,并提供更有针对性,更有效的预防程序。输入精密映射!

精确映射解决方案?

Precision Mapping is defined as conducting sampling at a much finer geographical resolution. Instead of mapping 5 schools in each district, potentially all schools would be examined in every subunit, thus eliminating errors caused by missing focal variation, allowing for highly targeted and efficient treatment which allows for a better management of resources. Ultimately, precision mapping allows for a more accurate understanding of disease foci distributions.(Tchuenté et al., 2018)

结论

There is a need for more precise appraisals of schistosomiasis prevalence that current mapping lacks. Addressing this problem using precision mapping will enable a better resources management, definition of target population and thus coverage. Ultimately, precision mapping goes a long way in allowing the schistosomiasis community to overcome this major obstacle on the road towards elimination.

未来研究的可能途径

确认跨空间的血吸虫病分布的变化至关重要。但是,有机会在整个时间的血吸虫病差异中进一步资源管理功效。然而,由于季节性,即多雨和干燥的季节,这些水体周围发生了传播,这些季节的大小会随着时间的流逝而波动。诸如洪水之类的自然事件可以增加个人与感染水的接触,从而导致随着时间的流行率变化。因此,探索更具动态的映射系统可能会增强传播中断和药物分布将是有用的。

This post is ammended from the全球血吸虫病联盟blog.

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