認識埃博拉,以及浩瀚的病毒世界

Behind the hellish Ebola epidemic ravaging West Africa lies an agent that fittingly embodies the mad contradictions of a nightmare. It is alive yet dead, simple yet complex, mindless yet prophetic, seemingly able to anticipate our every Move.

在埃博拉疫情侵襲西非的背後有一個恰好能體現一場噩夢矛盾之處的載體。它活着但已經死了，簡單而又複雜，盲目而又具先知性，似乎能夠預見我們的每一個舉動。

For scientists who study the evolution and behavior of viruses, the Ebola pathogen is performing true to its vast, ancient and staggeringly diverse kind. By all evidence, researchers say, viruses have been parasitizing living cells since the first cells arose on earth nearly four billion years ago.

對於研究病毒演變及行爲的科學家來說，埃博拉病原體的本質與數量龐大、歷史悠久、形態各異的各種病毒並無不同。研究人員稱，所有的證據都顯示，自大約40億年前地球上出現第一批細胞開始，病毒就一直寄生在活細胞當中。

Some researchers go so far as to suggest that viruses predate their hosts. That they essentially invented cells as a reliable and renewable resource they could then exploit for the sake of making new viral particles.

一些研究人員甚至表示，病毒先於宿主出現。它們基本上創造了細胞，並將其當做可靠的、可延續的資源，日後可以用來產生新病毒。

It was the primordial viral "collective," said Luis P. Villarreal, director of the Center for Virus Research at the University of California, Irvine, "that originated the capacity for life to be self-sustaining."

加州大學歐文分校(University of California, Irvine)病毒研究中心(Center for Virus Research)主任路易斯·維拉里爾(Luis P. Villarreal)說，“生命的自我維持能力源於”原始的病毒“團體”。

"Viruses are not just these threatening or annoying parasitic agents," he added. "They're the creative front of biology, where things get figured out, and they always have been."

“病毒不僅僅是危險的、令人討厭的寄生體，”他還說。“它們還處於生物學的創新前沿，爲問題的解決做着貢獻，它們也一直都是這樣的。”

Researchers are deeply impressed by the depth and breadth of the viral universe, or virome. Viruses have managed to infiltrate the cells of every life form known to science. They infect animals, plants, bacteria, slime mold, even larger viruses. They replicate in their host cells so prodigiously and stream out into their surroundings so continuously that if you collected all the viral flotsam afloat in the world's oceans, the combined tonnage would outweigh that of all the blue whales.

病毒世界的深度與廣度給研究人員留下了深刻的印象。病毒已成功侵入科學界已知的每一種生命形式的細胞中。它們會感染動物、植物、細菌、粘液菌，甚至是較大的病毒。它們在宿主細胞中大量複製，不斷涌入周圍環境。如果將全球海洋裏漂浮的所有病毒性物質收集起來，總重會超過所有藍鯨的重量。

Not that viruses want to float freely. As so-called obligate parasites entirely dependent on host cells to replicate their tiny genomes and fabricate their protein packages newborn viruses, or virions, must find their way to fresh hosts or they will quickly fall apart, especially when exposed to sun, air or salt.

病毒並非想要四處漂泊。由於所謂的專性寄生物完全依賴宿主細胞複製它們極小的基因組及合成蛋白，因此新產生的病毒或病毒粒子必須找到新宿主，否則它們就會迅速崩潰，特別是暴露在太陽、空氣或鹽中的時候。

"Drying out is a death knell for viral particles," said Lynn W. Enquist, a virologist at Princeton.

普林斯頓大學(Princeton University)病毒學家林恩·W·恩奎斯特(Lynn W. Enquist)說，“對於病毒粒子來說，乾燥的環境意味着死亡。”

How long shed virions can persist if kept moist and unbuffeted — for example, in soil or in body excretions like blood or vomit — is not always clear but may be up to a week or two. That is why the sheets and clothing of Ebola patients must be treated as hazardous waste and surfaces hosed down with bleach.

目前並不是十分清楚，如果保持潮溼且不受打擊，例如在土壤或血液、嘔吐物等人體排出的物質中，分離的病毒粒子能夠維持多長時間，但可能最多是一兩週。因此，埃博拉患者的牀單和衣服必須被當作危險廢物處理，表面都得用漂白劑沖洗。

Viruses are masters at making their way from host to host and cell to cell, using every possible channel. Whenever biologists discover a new way that body cells communicate with one another, sure enough, there's a virus already tapping into exactly that circuit in its search for new meat.

病毒善於通過一切可能的途徑，從一個宿主進入另一個宿主，從一個細胞進入另一個細胞。每當生物學家發現身體細胞交換信息的新方式後，果然就已經有病毒在利用這個通道，尋找新目標。

Reporting recently in Proceedings of the National Academy of Sciences, Karla Kirkegaard, a professor of microbiology and genetics at Stanford University School of Medicine, and her colleagues described a kind of "unconventional secretion" pathway based on so-called autophagy, or self-eating, in which cells digest small parts of themselves and release the pieces into their surroundings as signaling molecules targeted at other cells — telling them, for example, that it's time for a new round of tissue growth.

最近，斯坦福大學醫學院(Stanford University School of Medicine)微生物學及基因學教授卡拉·柯克加德(Karla Kirkegaard)和同事在《國家科學院院刊》(Proceedings of the National Academy of Sciences)發表文章描述了一種基於所謂的自噬的“非傳統分泌”途徑，即細胞消化一部分自身細胞質，然後將它們釋放到周圍的環境中，充當針對其他細胞的信號分子，比如，告訴它們，現在是進行新一輪組織生長的時候了。

The researchers determined that the poliovirus can exploit the autophagy conduit to cunning effect. Whereas it was long believed that new polio particles could exit their natal cell only by bursting it open and then seeking new cells to infect, the researchers found that the virions could piggyback to freedom along the autophagy pathway.

研究人員斷定，小兒麻痹症病毒能夠非常巧妙地利用這條自噬途徑來達成目的。從前，人們一直以爲，新的小兒麻痹症病毒粒子脫離產生這些病毒的細胞的唯一方式就是衝破細胞，尋找並感染新細胞，而研究人員發現病毒粒子能夠在自噬的過程中搭便車，從而獲得自由。

In that way, the virus could expand its infectious empire without destroying perfectly good viral factories en route. The researchers suspect that other so-called naked or nonenveloped viruses (like the cold virus and the enteroviruses that have lately plagued children in this country and Asia) could likewise spread through unconventional secretion pathways.

如此一來，病毒可以在不破壞完美的病毒工廠的情況下擴大傳染範圍。研究人員推測，其他所謂的裸病毒或無包膜病毒（比如最近困擾美國及亞洲兒童的感冒病毒和腸道病毒）同樣能夠通過非傳統分泌途徑傳播。

For their part, viruses like Ebola have figured out how to slip in and out of cells without kicking up a fuss by cloaking themselves in a layer of greasy lipids stolen from the host cell membrane, rather as you might foist a pill down a pet's throat by smearing it in butter.

埃博拉等病毒已經知道如何在從宿主細胞的細胞膜中盜取的一層脂質的掩護下悄悄進入、脫離細胞，就像你用抹上黃油的藥片去餵食寵物一樣。

According to Eric O. Freed, the head of the virus-cell interaction section at the National Cancer Institute, several recent technological breakthroughs have revolutionized the study of viruses.

美國國家癌症研究所(National Cancer Institute)病毒與細胞互動部門的主管埃裏克·O·弗裏德(Eric O. Freed)表示，最近幾項技術突破使病毒研究發生了巨大變革。

Advances in electron microscopy and super-resolved fluorescence microscopy — the subject of this year's Nobel Prize in Chemistry — allow scientists to track the movement of viral particles in and between cells, and to explore the fine atomic structure of a virus embraced by an antibody, or a virus clasped onto the protein lock of a cell.

電子顯微鏡和超高分辨率熒光顯微鏡的發展使得科學家能夠追蹤病毒粒子在細胞內及細胞間的活動，瞭解被抗體包圍的病毒或細胞蛋白結合位上的病毒的精細原子結構。今年的諾貝爾化學獎就頒發給了對超高分辨率熒光顯微鏡發展做出貢獻的科學家。

Through ultrafast gene sequencing and targeted gene silencing techniques, researchers have identified genes critical to viral infection and drug resistance. "We've discovered viruses we didn't even know existed," Dr. Freed said. And that could prove important to detecting the emergence of a new lethal strain.

研究人員已經通過快速基因測序及靶基因沉默技術，確定了對病毒感染及抗藥性至關重要的基因。弗裏德博士說，“我們發現了之前不知道的病毒。”事實可能會證明，這對新的致命病毒的探測非常重要。

Viruses are also notable for what they lack. They have no ribosomes, the cellular components that fabricate the proteins that do all the work of keeping cells alive.

病毒還有一個顯著特點，它們缺少一些東西。它們沒有核糖體——合成蛋白的細胞器，而蛋白是維持細胞存活的物質。

Instead, viruses carry instructions for co-opting the ribosomes of their host, and repurposing them to the job of churning out capsid and other viral proteins. Other host components are enlisted to help copy the instructions for building new viruses, in the form of DNA or RNA, and to install those concise nucleic texts in the newly constructed capsids.

但病毒會攜帶利用其宿主核糖體的指令，改變它們的用途，使它們合成大量衣殼及其他病毒蛋白。宿主細胞的其他部分則被用於幫助複製發展新病毒的指令——其形式表現爲DNA或RNA，並將這些簡單的核素安置在新合成的衣殼中。

"Viruses are almost miraculously devious," Dr. Freed said. "They're just bundles of protein and nucleic acid, and they're able to get into cells and run the show."

“病毒極其狡詐，”弗裏德博士說。“雖然它們只不過是一堆蛋白和核酸，它們卻能侵入細胞，控制細胞。”

"On the one hand, they're quite simple," Dr. Enquist said. "On the other hand, they may be the most highly evolved form of genetic information on the planet."

“一方面，它們非常簡單，"恩奎斯特博士說。“另一方面，它們可能是地球上進化程度最高的遺傳信息形式。"

Viruses also work tirelessly to evade the immune system that seeks to destroy them. One of the deadliest features of the Ebola virus is its capacity to cripple the body's first line of defense against a new pathogen, by blocking the release of interferon.

病毒還堅持不懈地躲避着試圖摧毀它們的免疫系統。埃博拉病毒能夠阻礙干擾素的釋放，突破人體防禦新病菌的第一道防線，這也是該病毒最致命的特徵之一。

"That gives the virus a big advantage to grow and spread," said Christopher F. Basler, a professor of microbiology at Mount Sinai School of Medicine.

西奈山醫學院(Mount Sinai School of Medicine)微生物學教授克里斯托弗·F·巴斯勒(Christopher F. Basler)說，“這給了這種病毒巨大的優勢，有助於它的增長和傳播。”

At the same time, said Aftab Ansari of Emory University School of Medicine, the virus disables the body's coagulation system, leading to uncontrolled bleeding. By the time the body can rally its second line of defense, the adaptive immune system, it is often too late.

埃默裏大學醫學院的(Emory University School of Medicine)的阿夫塔卜·安薩里(Aftab Ansari)表示，與此同時，病毒破壞了人體凝血系統，導致人體不可控制地出血。等到人體築起第二道防線——適應性免疫系統時，通常爲時已晚。

Yet the real lethality of Ebola, Dr. Ansari said, stems from a case of mistaken location, a zoonotic jump from wild animal to human being. The normal host for Ebola virus is the fruit bat, in which the virus replicates at a moderate pace without killing or noticeably sickening the bat.

但安薩里博士表示，埃博拉病毒真正的殺傷力源於錯放了位置，從野生動物跨物種感染了人類。埃博拉病毒的宿主通常是果蝠，病毒在不使果蝠死亡或明顯患病的情況下穩步複製。

"A perfect parasite is able to replicate and not kill its host," Dr. Ansari said. "The Ebola virus is the perfect parasite for a bat."

“完美的寄生生物能夠複製，且不殺死宿主，”安薩里說。“埃博拉病毒是蝙蝠身上的完美寄生物。”