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比SARS更致命:蝙蝠病毒MERS是如何成為人類殺手的

比SARS更致命:蝙蝠病毒MERS是如何成為人類殺手的

Erika Fry 2014-09-01
編者按:本文是《財(cái)富》雜志探討傳染現(xiàn)象的系列文章的開篇之作。埃博拉病毒近來讓全球陷于恐慌之中,不過在今年早些時(shí)候,全球衛(wèi)生部門官員最為頭疼的,是號(hào)稱SARS姊妹,但比其更致命的MERS病毒。今年夏天,MERS病毒的蔓延趨勢似乎有所減緩,但病原體并未消失。更讓人擔(dān)憂的是,流行病學(xué)專家至今還沒有搞清楚這種病毒的傳染途徑。

????SARS在人群中的傳染性比目前的MERS強(qiáng)得多,但它的致命性卻較弱,只有10%的感染者死亡,而MERS則有35%。因此MERS目前雖然不是緊迫的威脅,但也具有潛在的危險(xiǎn)性,一旦病毒產(chǎn)生更具傳染性的變種,就隨時(shí)可能在人類之間或動(dòng)物和人類之間傳播。

????相關(guān)視頻:病毒大小的粒子試圖進(jìn)入細(xì)胞

????不過與據(jù)信只會(huì)在人類和動(dòng)物間傳播幾次的SARS病毒不同,MERS病毒(現(xiàn)在我們都知道它存在了)似乎可以不斷跳越物種——這種病毒通過許多種不同的動(dòng)物傳染病事件實(shí)現(xiàn)了擴(kuò)散,這一傳染模式十分不可思議。

????人們在拼湊謎底的過程中,發(fā)現(xiàn)似乎這一病毒同SARS一樣,源頭來自蝙蝠。蝙蝠帶有許多糟糕的病毒(從埃博拉病毒,到狂犬病毒,再到SARS病毒),動(dòng)物王國擁有向?qū)櫸?、牲畜和人類傳播病毒的悠久歷史——通常通過唾液或排泄物。今年7月,科學(xué)家發(fā)布的最新研究報(bào)告顯示,在南非翼足棕蝠的排泄物中發(fā)現(xiàn)了一種病毒,與MERS病毒屬于同種,擁有迄今為止最為匹配的基因。

????科學(xué)家懷疑是蝙蝠將MERS傳給了單峰駱駝。動(dòng)物們的MERS抗體呈陽性的情況至少可以追溯到1992年(產(chǎn)生抗體即說明曾經(jīng)遭到感染)。最近,有75%的沙特阿拉伯駱駝都被檢測出了病毒抗體——其中35%的駱駝身上仍有活躍的病毒。而遠(yuǎn)到埃及、阿曼、以及西班牙的加那利群島的駱駝上也帶有抗體。

????流行病學(xué)專家還不確定病毒是否首先是由駱駝傳給人類的,但這是一個(gè)可能的源頭。至少在一起事件中,駱駝被證明是罪魁禍?zhǔn)住瓷衔拈_篇提到的那頭駱駝的主人?!?月底,沙特阿拉伯的一個(gè)研究小組在《新英格蘭醫(yī)學(xué)雜志》(New England Journal of Medicine)上發(fā)表文章稱,死者和被感染的駱駝身上的病毒的全部基因組序列完全相同?!慷阎牡谝粋€(gè)死于MERS的患者(一個(gè)住在沙特阿拉伯比沙的商人)也與駱駝?dòng)兄H密接觸:他豢養(yǎng)了4頭駱駝作為寵物。

????這種聯(lián)系是講得通的:在阿拉伯半島,駱駝無所不在,被認(rèn)為是高貴的動(dòng)物,這顯然給動(dòng)物傳染病提供了機(jī)會(huì)。

????即便是健康的駱駝也會(huì)流唾液,它們還會(huì)通過鼻子和糞便傳播病毒??ㄋ柫餍胁W(xué)專家最近通過研究發(fā)現(xiàn),許多受感染的駱駝奶中也包含MERS病毒。(不過目前尚不明白,究竟是駱駝奶直接被污染了,還是由于小駱駝的吮吸而遭到污染。)

????此外,與動(dòng)物的親密接觸也并不罕見。駱駝在中東作為營生和娛樂的來源之一,通常被當(dāng)作馬一樣使用,并作為選美比賽的選手出場。駱駝奶和駱駝肉都可食用,有時(shí)這些未經(jīng)加工的產(chǎn)品就是病毒可能的傳播途徑。主人們將駱駝看作寵物和牲口,會(huì)在喂食、看護(hù)和接生時(shí)與它們親密接觸。而世界衛(wèi)生組織和許多政府已經(jīng)建議人們在做這些事情時(shí)戴好面罩和手套。(一些沙特阿拉伯人,尤其是熱愛駱駝的人,認(rèn)為將駱駝看作傳播致命疾病的嫌疑犯并提出這樣的指南和建議,是一種對(duì)他們的冒犯。他們在YouTube上發(fā)布了親吻駱駝的視頻表示抗議。)

????不過,如果駱駝是動(dòng)物傳染病的一環(huán),那就產(chǎn)生了另一個(gè)更大的疑問:為何MERS病毒沒有早些時(shí)候跨物種傳播呢?流行病學(xué)專家表示,該問題最好的答案是,它幾乎毫無疑問地確實(shí)被傳播了,只是我們沒有發(fā)現(xiàn)而已。

????至少有一次MERS的爆發(fā)——2012年5月,在約旦一家醫(yī)院中,有13人被感染,事后才被發(fā)現(xiàn)——早于MERS病毒的發(fā)現(xiàn)(當(dāng)時(shí),約旦的醫(yī)生認(rèn)為那是肺炎癥狀)。最近,沙特阿拉伯和卡塔爾的監(jiān)測也發(fā)現(xiàn)有許多人擁有MERS抗體(即曾經(jīng)被MERS感染過),或是無癥狀感染者,即攜帶病毒但沒有出現(xiàn)癥狀。這意味實(shí)際MERS的感染病例數(shù)遠(yuǎn)遠(yuǎn)多于官方記錄的數(shù)目。

????盡管MERS病毒和埃博拉病毒十分可怕,但大多數(shù)傳染病專家都表示,疾病爆發(fā)將會(huì)讓他們愈發(fā)謹(jǐn)慎和小心,而不是恐懼。而讓他們睡不著覺的,永遠(yuǎn)是下一種病毒。(財(cái)富中文網(wǎng))

????譯者:嚴(yán)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.

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