发布日期：2019-11-14
流行病的扩散
流行病的扩散
发布日期：2020-03-19 09:17
黑死病一般被认为是淋巴性鼠疫，它由里海地区传入欧洲，并于1346年由蒙古人携带扩散至卡法地区。通过在船舶中的老鼠身上的跳蚤，黑死病传播到欧洲的各个港口。在随后的七年中，这种病杀死了欧洲1/3的人口。
中世纪时期，传染病的传播较容易预测，船只可以携带疾病进行长距离运输，如墨水般从地中海地区向整个欧洲大陆扩散。为了防止疾病传播，人们开始减少活动：大多数人只在他们家乡周边几英里的范围内活动，所以传染病只能一个村庄接一个村庄地传播。
当人类的移动性较低的时候，像黑死病这样的传染病会像墨水一样（左图）缓慢扩散，并能够被预测。今天，人类通过纵横交错的路径会瞬间在全球范围内移动（右图），造成传染病蔓延的可怕后果。（来源：B. Balcan et al., Proc. Natl. Acad. Sci.USA 106, 21484-21489 (2009).)
今天的状况已经截然不同，人们可以在一天内进行环球旅行，并且公路、铁路和水上交通可以进行快速和长距离的运输。由于致命性流感病毒，如H5N1（禽流感）和H1N1（猪流感）的传播，人类移动性的增强已经得到了更多的关注。尽管我们已经认识到现在和14世纪相比，人们增强了多少移动性，许多流行病预测模型仍然假定流行性疾病是以平滑的界面向外扩散，这主要是因为我们极度缺乏有关人类移动模式的信息。
一旦考虑这些模式，流行病学的复杂性将大大增加：起初看起来是纯医学性的问题，现在需要和社会科学不同的领域联系起来，比如交通网络的类型以及它们的运用模式。在局部范围内，传染病模型需要考虑各种人类移动模型，例如这些模型可以估计我们在日常生活会遇到多少人。人类迁移、社会交往（实际上关注的是性行为）的特性和模式，以及对疾病的易感性的变化都需要考虑社会经济统计的影响：贫富和文化都对会对这些因素产生影响。简言之，在今天要了解疾病的传播，需要有真正的跨学科的视角，来认识许多网络和交互模式之间复杂的相互作用。
实现这种目标的重要性和紧迫性是毋庸置疑的。艾滋病是目前世界上第三大致命的疾病，仅在撒哈拉以南非洲地区每年就有200万人死于艾滋病。在那片区域，年龄在15到49岁的人群中，约20人中就有1人是HIV阳性携带者，到了南部非洲（通常指南非、纳米比亚等五国）进一步增加至每7人中有1人为阳性。这种疾病在一定程度上造成非洲大陆人口的预期寿命仅为50岁上下，并阻碍了该地区的经济增长。同时，大多数流行病专家认为，一种与曾在全世界范围内导致成千上万人死亡的在1957至1958年和1968至1969年蔓延的病毒杀伤力相当的新型流感将在无法预测的情况下不可避免地发生。尽管抗击这些疾病要部分地依靠研制新药和了解病原体的生物成分，我们却比以往任何时候都需要研究人类移动和行为模式，进而了解病毒的扩散方式。只有做到这一点，有效的疫苗和隔离策略才能得以出现并发挥作用。
以下为英文原文：
The Black Death, generally thought to be bubonic plague, spread into Europe from the Caspian sea, brought by Mongols attacking the city of Kaffa in 1346. Carried by fleas on ship rats, it was ferried to ports throughout Europe. Over the next seven years it killed about a third of the population.
The transmission of an infectious disease in the Middle Ages is fairly predictable. While ships could transport the plague over long distances, its spread across the European continent from the Mediterranean ports resembles the steady advance of an inkblot. Human mobility was then very low: most people barely ventured a few miles beyond their hometown, and so infection advanced more or less village by village.
When human mobility was low, infectious diseases such as the Black Death spread slowly and predictably, like an inkblot (left). Today, humans criss-cross the globe in an instant (right), with potentially dire consequences for disease epidemics. (Credit (right): from B.Balcan et al., Proc. Natl. Acad. Sci. USA 106, 21484-21489 (2009).)
It’s different today. Individuals cross the globe in less than a day, while road, rail and water transport also allow rapid, long-distance movements. Increased human mobility recently has become a focus of attention because of fears about the spread of particularly virulent forms of influenza, such as H5N1 (bird flu) and H1N1(swine flu). Yet despite recognition of how much more mobile we are than in the fourteenth century, many models of epidemics still assume that diseases spread in smoothly advancing fronts. Largely this is due to a sheer lack of information about what patterns of human movement really look like.
Once these patterns are taken into account, the complexity of epidemiology is greatly increased: what seems at first like a purely medical question becomes linked to quite different areas of social science, such as the nature of transportation networks and their patterns of usage. At a local scale, modeling of epidemics might need to take account of the kinds of human movement models, which could determine for example how many people we encounter in our daily routines. Human movements, the nature and patterns of our social (and indeed sexual) intercourse, and variations in susceptibility to disease must also acknowledge the influence of socioeconomic demographics: affluence/poverty and culture affect all these things. In short, understanding the spread of disease today demands a truly cross-disciplinary perspective that, among other things, recognizes the complex interplay of many networks and modes of interaction.
The vital and urgent importance of that objective is in no doubt. AIDS is now the third biggest cause of premature death in the world, and kills two million people a year in sub-Saharan Africa alone. Around one in 20 people in that region aged between15 and 49 are HIV-positive, reaching a level of almost one in seven in southern Africa. The disease is partly responsible for a life expectancy of around 50and for preventing economic growth in the continent. Meanwhile, epidemiologists generally agree that a new flu pandemic, comparable to those in 1957–8 and1968–9 that killed millions worldwide, is inevitable and yet impossible to predict. Although combating such major health problems is partly a question of developing new drugs and understanding the biology of the pathogens, more than ever before it relies on understanding how the diseases are transmitted and spread through patterns of human movement and behavior. Only then, for example, can effective vaccination and quarantine strategies be devised.
参考文献：
Ball, Philip. Why Society is a Complex Matter: Meeting Twenty-First Century Challenges with a New Kind of Science.Springer-Verlag: Berlin, 2012
（英）菲利普•鲍尔著, 韩昊英译, 赖世刚校. 社会为何如此复杂：用新科学应对二十一世纪的挑战. 北京：科学出版社,2015.
本文作者在原书的基础上，重新撰写了文字。
作者简介：韩昊英
目前为浙江大学城乡规划学和公共管理学的教授、博士生导师，学术背景为建筑学、城乡规划学和公共管理学，曾在清华大学、日本东京大学、韩国首尔国立大学和加拿大多伦多大学攻读学位或访学研究。韩昊英从小生活在城市，热爱城市的历史和文化，喜欢观察和丰富多彩的城市生活。
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