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比SARS更致命:蝙蝠病毒MERS是如何成为人类杀手的

Erika Fry 2014年09月01日

编者按:本文是《财富》杂志探讨传染现象的系列文章的开篇之作。埃博拉病毒近来让全球陷于恐慌之中,不过在今年早些时候,全球卫生部门官员最为头疼的,是号称SARS姊妹,但比其更致命的MERS病毒。今年夏天,MERS病毒的蔓延趋势似乎有所减缓,但病原体并未消失。更让人担忧的是,流行病学专家至今还没有搞清楚这种病毒的传染途径。

    然而,对一些人来说,MERS病毒之所以如此可怕,就在于我们不知道它还有多少谜团尚未被发掘。比如最关键的:人类究竟是如何被它感染的,又是如何传染给其他人的。人们已经掌握了一些线索,病骆驼就是其中之一,但目前来看,蝙蝠、骆驼、医院、没有做好防护措施的医护人员、不干净的桌面以及政治因素,都需要为此承担一定责任。一位澳大利亚流行病学专家用“悖论”来描述MERS的扩散,他最近甚至提出,生物恐怖主义也许扮演了推手的角色。

    与此同时,自从首次发现人类感染MERS病毒之后的两年以来,相关病例和死亡数一直在持续攀升(而且,现在的世界还笼罩在埃博拉病毒的阴影下)。就在上周,沙特阿拉伯又报告了两起新病例。

    世界卫生组织紧急状态委员会已经就MERS召开了6次会议,根据世卫组织的最新计算,35%的感染者都会死亡。不过,虽然MERS已经受到全球医疗团体专家的高度重视,它仍然没有被看作“引起国际关注的突发公共卫生事件”。

    尽管如此,由于今年夏天和秋天会有大量朝圣者前往沙特阿拉伯,MERS在人群中引起了不安的骚动。斋月是做小朝(许多穆斯林前往麦加进行的一种宗教仪式)的旺季,7月份,有超过600万人来到沙特阿拉伯。而在10月,全球各地会有更多人来到伊斯兰教的圣城麦加进行大朝——根据伊斯兰教的传统,如果身体和经济状况允许,穆斯林一生中至少需要进行一次大朝。全球卫生部门的一些官员对此感到担忧,因为在10月进行朝觐仪式的5天内,这座城市会涌入250万人。由于MERS病毒可能会突变成更具传染性的恶性病毒,这一盛会也许将使MERS变成全球下一流行性疾病。

    相应的,科学家正在努力理解,为何一种在骆驼中传播了几十年的病毒突然找上了人类,并开始在全世界传播。

    从许多方面来看,MERS病毒的故事都不陌生,它只是公共卫生部门官员近年来新发现的许多病原体中的最新品种。与包括艾滋病(HIV)、SARS、H5N1(禽流感)和H1N1(猪流感)在内的近三分之二新型疾病一样,MERS也是通过动物传染病或是一些巧合事件,从动物传到人类身上,开始给人类带来困扰。

    大卫•奎曼表示,这类事件变得越来越普遍,不仅是因为它们越来越经常被发现,还因为发生这类事件的机会变得越来越多。他就此撰写了一部作品,《致命接触:全球大型传染病探秘之旅》(Spillover: Animal Infections and the Next Human Pandemic)。人类与动物之间的接触一直存在,但是现代社会的发展——比如在热带雨林中修路、搭帐篷,或工厂化的畜牧方式——增加了接触的范围和频率。此外,疾病在现代社会也能传播得更远、更快。

    就以SARS(重症急性呼吸综合征)为例。2003年,这种冠状病毒在全世界造成了恐慌。在短短一个月内,就有8,100人受到感染,其中774人最终死亡。

    SARS最早于2002年11月在中国广东被确定,人们认为这种病毒来源于蝙蝠,通过果子狸(一种类似猫的动物,在野味市场有售,中国部分地区将其视为美味佳肴)传给了人类。一旦人类感染,这种病毒便可以通过空气以极为恐怖的速度和范围传染——最著名的一次,病毒感染了居住在香港淘大花园的321位居民(2006年一篇研究SARS爆发的论文发现,这种病毒是通过浴室地漏进入公寓的)。SARS病毒最终借助一些“超级传染源”,即特别能够传播该病的个人,进入了超过30个国家。比如,一名来自广东的医生,在留宿香港京华国际酒店(Metropole Hotel)期间将SARS病毒传给了13个人,他们随后将病毒带入了加拿大、新加坡和越南。

    Yet what makes MERS so scary to some, is just how much about it remains in the realm of mystery—starting with something critical: how exactly humans become infected and how they pass the virus on to others. There are clues with MERS—the sick camels, for one—but currently, bats, camels, hospitals, unprotected health care workers, unclean surfaces and politics have all shouldered a bit of the speculative blame. One Australian epidemiologist, citing “paradoxes” involved in MERS’ spread, recently even suggested that bioterrorism may have a role.

    Meanwhile, two years since MERS was first discovered in humans—and now in the shadow of Ebola—the tally of patients and fatalities continues to climb. Saudi Arabia reported two new cases just last week.

    The WHO has convened six Emergency Committee meetings on MERS, which by the health organization’s latest reckoning kills 35% of its victims. But while MERS has earned the carefully trained eye of the world’s medical community, it has not yet been deemed a “public health emergency of international concern.”

    Even so, it has made for an unsettling state of affairs given the number of pilgrims traveling to Saudi Arabia this summer and fall. Ramadan, the peak season to perform the Umrah (a religious journey to Mecca that many Muslims make), drew more than 6 million to the country in July. And in October, many more people from all over the world will crowd into Islam’s holy city for the Hajj—a pilgrimage to Mecca that Islamic tradition requires Muslims (who are physically and financially able) to undertake at least once during their lifetimes. Some global health officials fear that, as 2.5 million additional people converge on a single city during a five-day period in October, the stage may be set to turn MERS—which is potentially one mutation away from becoming a more virulent, transmissible disease—into the world’s next pandemic.

    Accordingly, scientists are scrambling to understand how a virus that had been circulating in camels for decades suddenly took root in humans and started spreading around the world.

    In many ways, MERS is a familiar story, just the latest in a number of newly-discovered pathogens to have landed on the radar of public health officials in recent years. As with nearly two-thirds of emerging diseases—including HIV, SARS, H5N1 (bird flu), and H1N1 (swine flu)—MERS started making trouble for humans after a zoonotic event, or that random moment when it jumped from an animal to humans.

    These events are increasingly common, both because they’re being detected more often, and because there’s more and more opportunity for such events to occur, says David Quammen, who has written a book, Spillover: Animal Infections and the Next Human Pandemic on the subject. Interactions between humans and animals have happened forever, but modern development—such as the building of roads and timber camps in tropical forest, or factory farming—has increased the scale and frequency of them. Plus disease can travel much further and faster these days.

    Take SARS, or Severe Acute Respiratory Syndrome, the coronavirus that gave the world a scare in 2003 when it infected 8100 people and killed 774 of them in a matter of months.

    First identified in China’s Guangdong Province in November 2002, SARS is thought to have originated in bats and been passed to humans by way of the civet, a cat-like animal that was sold in wildlife markets and eaten as a delicacy in parts of China. Once in humans, the virus spread through the air with terrifying speed and reach—most notably when it infected 321 residents of Amoy Gardens, a Hong Kong apartment complex (a 2006 paper on the outbreak found that the virus entered apartments via bathroom floor drains.) The virus ultimately traveled to more than 30 countries, helped along by a handful of “super-spreaders” or individuals who transmit disease particularly effectively. While staying in Hong Kong’s Metropole Hotel, for example, a doctor from Guangdong infected 13 people including those who carried SARS to Canada, Singapore and Vietnam.

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