比SARS更致命：蝙蝠病毒MERS是如何成为人类杀手的

    SARS在人群中的传染性比目前的MERS强得多，但它的致命性却较弱，只有10%的感染者死亡，而MERS则有35%。因此MERS目前虽然不是紧迫的威胁，但也具有潜在的危险性，一旦病毒产生更具传染性的变种，就随时可能在人类之间或动物和人类之间传播。

    相关视频：病毒大小的粒子试图进入细胞

    不过与据信只会在人类和动物间传播几次的SARS病毒不同，MERS病毒（现在我们都知道它存在了）似乎可以不断跳越物种——这种病毒通过许多种不同的动物传染病事件实现了扩散，这一传染模式十分不可思议。

    人们在拼凑谜底的过程中，发现似乎这一病毒同SARS一样，源头来自蝙蝠。蝙蝠带有许多糟糕的病毒（从埃博拉病毒，到狂犬病毒，再到SARS病毒），动物王国拥有向宠物、牲畜和人类传播病毒的悠久历史——通常通过唾液或排泄物。今年7月，科学家发布的最新研究报告显示，在南非翼足棕蝠的排泄物中发现了一种病毒，与MERS病毒属于同种，拥有迄今为止最为匹配的基因。

    科学家怀疑是蝙蝠将MERS传给了单峰骆驼。动物们的MERS抗体呈阳性的情况至少可以追溯到1992年（产生抗体即说明曾经遭到感染）。最近，有75%的沙特阿拉伯骆驼都被检测出了病毒抗体——其中35%的骆驼身上仍有活跃的病毒。而远到埃及、阿曼、以及西班牙的加那利群岛的骆驼上也带有抗体。

    流行病学专家还不确定病毒是否首先是由骆驼传给人类的，但这是一个可能的源头。至少在一起事件中，骆驼被证明是罪魁祸首——即上文开篇提到的那头骆驼的主人。【6月底，沙特阿拉伯的一个研究小组在《新英格兰医学杂志》（New England Journal of Medicine）上发表文章称，死者和被感染的骆驼身上的病毒的全部基因组序列完全相同。】而已知的第一个死于MERS的患者（一个住在沙特阿拉伯比沙的商人）也与骆驼有着亲密接触：他豢养了4头骆驼作为宠物。

    这种联系是讲得通的：在阿拉伯半岛，骆驼无所不在，被认为是高贵的动物，这显然给动物传染病提供了机会。

    即便是健康的骆驼也会流唾液，它们还会通过鼻子和粪便传播病毒。卡塔尔流行病学专家最近通过研究发现，许多受感染的骆驼奶中也包含MERS病毒。（不过目前尚不明白，究竟是骆驼奶直接被污染了，还是由于小骆驼的吮吸而遭到污染。）

    此外，与动物的亲密接触也并不罕见。骆驼在中东作为营生和娱乐的来源之一，通常被当作马一样使用，并作为选美比赛的选手出场。骆驼奶和骆驼肉都可食用，有时这些未经加工的产品就是病毒可能的传播途径。主人们将骆驼看作宠物和牲口，会在喂食、看护和接生时与它们亲密接触。而世界卫生组织和许多政府已经建议人们在做这些事情时戴好面罩和手套。（一些沙特阿拉伯人，尤其是热爱骆驼的人，认为将骆驼看作传播致命疾病的嫌疑犯并提出这样的指南和建议，是一种对他们的冒犯。他们在YouTube上发布了亲吻骆驼的视频表示抗议。）

    不过，如果骆驼是动物传染病的一环，那就产生了另一个更大的疑问：为何MERS病毒没有早些时候跨物种传播呢？流行病学专家表示，该问题最好的答案是，它几乎毫无疑问地确实被传播了，只是我们没有发现而已。

    至少有一次MERS的爆发——2012年5月，在约旦一家医院中，有13人被感染，事后才被发现——早于MERS病毒的发现（当时，约旦的医生认为那是肺炎症状）。最近，沙特阿拉伯和卡塔尔的监测也发现有许多人拥有MERS抗体（即曾经被MERS感染过），或是无症状感染者，即携带病毒但没有出现症状。这意味实际MERS的感染病例数远远多于官方记录的数目。

    尽管MERS病毒和埃博拉病毒十分可怕，但大多数传染病专家都表示，疾病爆发将会让他们愈发谨慎和小心，而不是恐惧。而让他们睡不着觉的，永远是下一种病毒。（财富中文网）

    译者：严匡正

    SARS was far more transmissible among humans than MERS currently is, but it was also less lethal, killing roughly 10% of its victims compared to the 35% of patients who have died from MERS. This makes MERS a less imminent threat, but also a potentially terrifying one should it mutate into a more transmissible form, an opportunity the virus gets every time it spreads between humans, or from animals to humans.

    Watch: Video of virus-sized particle trying to enter cell

    But unlike SARS, which is believed to have jumped from humans to animals just a few times, MERS (now that we know it exists) appears to be jumping repeatedly—the spread of the virus propelled along by a number of scattered separate zoonotic events, a pattern that’s mysterious for a number of reasons.

    While that puzzle is still being pieced together, it’s likely that this story begins, as SARS did, in a bat. Reservoirs for many a nasty virus (from Ebola to rabies to SARS), bats have a long history of spreading disease—typically through saliva or their tiny droppings—to others in the animal kingdom, from house pets to livestock to humans. In July, scientists published findings that a virus found in the feces of a Cape serotine, a South African bat, was of the same species—and offered the closest genetic match yet—to the MERS-CoV.

    Scientists suspect it was a bat that brought MERS to dromedary camels; the animals have tested positive for MERS antibodies dating back to at least 1992 (antibodies are a sign of previous infection). More recently, antibodies have been found in 75% of camels in Saudi Arabia—the virus was active in 35% of them—as well as in camels many countries away in Egypt, Oman, and the Canary Islands off the coast of Spain.

    While epidemiologists aren’t certain that the virus’ first leap to humans came via camels, the animal is a likely source. The camel has been proven to be the culprit in at least one instance—that of our 40-something-year-old camel owner near Jeddah. (In late June, a team of Saudi researchers reported in the New England Journal of Medicine that full genome sequences in the virus found in both the human victim and the infected camel were identical.) And the first known patient to die of MERS, a businessman living in Bishah, Saudi Arabia, also had exposure to them: he kept four camels as pets.

    The linkage makes sense: On the Arabian Peninsula, where camels are ubiquitous and considered honorable beasts, there is certainly opportunity for zoonotic events.

    Slobbering animals even when healthy, camels shed virus through their noses and stool; recent epidemiological research from Qatar also found the milk from many infected camels contained MERS. (It’s unclear whether the milk was infected directly by the camel or contaminated through a calf’s suckling.)

    Close contact with the animals, moreover, is hardly rare. A source of livelihood and entertainment, camels in the Middle East are raced like horses and trotted out in beauty pageants (as contestants). They’re regularly consumed for milk and meat, sometimes in the raw forms that have been flagged as possible transmission routes. Kept as pets and livestock, owners are intimately involved in the feeding, care and birthing of the creatures, contact that the WHO and a number of governments now advise be done with facial masks and gloves. (Offended by such guidance and the suggestion the animal has anything to do with transmitting a lethal disease, some Saudis, particularly loyal to the animal, have posted videos of themselves on YouTube kissing camels.)

    But if camels are the zoonotic link, then it raises another, perhaps bigger mystery: why didn’t MERS jump sooner? Here, the best answer, epidemiologists say, is that it almost certainly did—we just didn’t notice.

    At least one MERS outbreak—which infected 13 people in a Jordan hospital in May 2012 and was discovered in hindsight—predates the discovery of MERS (at the time, doctors in Jordan believed the illness to be pneumonia). Recent surveillance efforts in Saudi Arabia and Qatar have also turned up a number of individuals who either have MERS antibodies (meaning they once had the virus) or are asymptomatic—meaning they have the virus but show no sign of it—suggesting there are far more cases than officially tallied.

    As scary as MERS is—and Ebola, too, for that matter—most infectious disease experts say the outbreaks are cause for cautious vigilance, not panic. What keeps them up at night, rather, is the next one.