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翻译人员: Ethan Huang
校对人员: Yolanda Zhang
00:07
For almost a decade, scientists chased
the source of a deadly new virus
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在近十年间,从中国的
最高峰到最偏远的洞穴里,
00:12
through China’s tallest mountains
and most isolated caverns.
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科学家们一直在追寻一种
新型致命病毒的源头。
00:16
They finally found it here:
in the bats of Shitou Cave.
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他们最终在“石头洞”的蝙蝠
身上找到了答案。
00:21
The virus in question was a coronavirus
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人们所找寻的病毒是
一种在 2003 年引发了
00:23
that caused an epidemic
of severe acute respiratory syndrome,
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严重急性呼吸系统
综合症流行病,
00:27
or SARS, in 2003.
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简称非典型肺炎(SARS)的冠状病毒。
00:30
Coronaviruses are a group of viruses
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冠状病毒是一群表面有着
棘突蛋白的病毒,
00:32
covered in little protein spikes
that look like a crown—
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看起来很像皇冠——
00:36
or "corona" in Latin.
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在拉丁文中意为“冠状物”。
00:38
There are hundreds
of known coronaviruses.
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目前已知的冠状病毒有数百种。
00:41
Seven of them infect humans,
and can cause disease.
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其中的七种可以传染给人类
并且引起疾病。
00:45
The coronavirus SARS-CoV causes SARS,
MERS-CoV causes MERS,
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冠状病毒 SARS-CoV 可引起非典型肺炎,
MERS-CoV 可引起中东呼吸系统综合征,
00:51
and SARS-CoV-2 causes
the disease COVID-19.
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而 SARS-CoV-2 则可引起
新型冠状病毒肺炎(COVID-19)。
00:56
Of the seven human coronaviruses,
four cause colds,
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七种会感染人类的冠状病毒中,
有四种会导致感冒,
01:01
mild, highly contagious infections
of the nose and throat.
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即症状温和
且具有高传染性的鼻喉感染。
01:05
Two infect the lungs,
and cause much more severe illnesses.
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有两种会感染肺部并且
引起更严重的疾病。
01:10
The seventh, which causes COVID-19,
has features of each:
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引起 COVID-19 的第七种病毒
综合了上述两类的特征:
01:14
it spreads easily,
but can severely impact the lungs.
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不仅极易传播,
而且会严重地影响肺部。
01:18
When an infected person coughs,
droplets containing the virus spray out.
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当受感染者咳嗽时,含有病毒
的飞沫就会喷溅而出。
01:23
The virus can infect a new person when
the droplets enter their nose or mouth.
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当飞沫进入其他人的鼻腔或口腔时,
这些人就会被病毒感染。
01:28
Coronaviruses transmit best
in enclosed spaces,
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冠状病毒在封闭的
空间内最易传播,
01:31
where people are close together.
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在这些地方人与人之间距离很近。
01:33
Cold weather keeps their delicate casing
from drying out,
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寒冷的天气可以防止病毒的
精密外壳变干,
01:36
enabling the virus to survive
for longer between hosts,
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使得它们在宿主之间
传播时能够存活更长时间。
01:40
while UV exposure from sunlight
may damage it.
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但是紫外线的照射
可能会消灭它们。
01:43
These seasonal variations matter more
for established viruses.
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这些季节上的变化对于
已经存在的病毒影响更大。
01:47
But because no one is yet immune
to a new virus,
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但是因为至今没有任何人
对新出现的病毒免疫,
01:50
it has so many potential hosts that it
doesn’t need ideal conditions to spread.
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所以它有很多不需要在理想环境下
就可以感染的潜在宿主。
01:55
In the body, the protein spikes embed
in the host’s cells and fuse with them—
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进入人体后,棘突蛋白会嵌入
宿主的细胞内并与它们融合——
02:00
enabling the virus to hijack
the host cell’s machinery
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这个过程让病毒能够控制
宿主细胞的运转体系,
02:02
to replicate its own genes.
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以复制其自身的遗传基因。
02:05
Coronaviruses store their genes on RNA.
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冠状病毒把它们的基因
储存在 RNA 内。
02:08
All viruses are either RNA viruses
or DNA viruses.
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所有病毒都是 RNA 或者 DNA 病毒。
02:12
RNA viruses tend to be smaller,
with fewer genes,
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RNA 病毒通常更小,
携带更少的基因,
02:15
meaning they infect many hosts
and replicate quickly in those hosts.
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这意味着它们可以感染众多宿主,
并且在宿主体内快速复制。
02:20
In general, RNA viruses don’t have
a proofreading mechanism,
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一般来说,RNA 病毒没有校对机制,
02:24
whereas DNA viruses do.
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而 DNA 病毒则有。
02:27
So when an RNA virus replicates,
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因此,当 RNA 病毒进行自我复制时,
02:29
it’s much more likely to have
mistakes called mutations.
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更有可能发生错误,即所谓的“突变”。
02:33
Many of these mutations are useless
or even harmful.
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大多数的突变都是对其自身
无用,甚至是无益的。
02:37
But some make the virus better suited
for certain environments—
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但是有一些变异可以帮助病毒
更加适应某些特定的环境——
02:40
like a new host species.
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比如说新的宿主物种。
02:42
Epidemics often occur when a virus
jumps from animals to humans.
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传染病通常在病毒从动物
传染到人类时出现,
02:47
This is true of the RNA viruses
that caused
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比如由 RNA 病毒导致的
02:49
the Ebola, Zika, and SARS epidemics,
and the COVID-19 pandemic.
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埃博拉、寨卡和非典传染病,以及
COVID-19 全球性大流行病。
02:55
Once in humans, the virus still mutates—
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进入人体以后,
病毒仍然会发生突变——
02:58
usually not enough to create a new virus,
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虽然这种突变不足以
创造新型的病毒,
03:00
but enough to create variations,
or strains, of the original one.
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但足以使原本的病毒
产生变化,或产生新株系。
03:05
Coronaviruses have a few key differences
from most RNA viruses.
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相比大多数 RNA 病毒,
冠状病毒有几个主要的差别。
03:09
They’re some of the largest,
meaning they have the most genes.
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它们是体积最大的 RNA 病毒,
有着最多的遗传基因,
03:13
That creates more opportunity
for harmful mutations.
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也就更可能出现
对自身有害的变异。
03:16
To counteract this risk,
coronaviruses have a unique feature:
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为了抵消这种风险,冠状病毒
展现出了一种独有的特性:
03:21
an enzyme that checks for replication
errors and corrects mistakes.
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一种可以检验基因复制错误
并进行纠正的酶。
03:25
This makes coronaviruses
much more stable,
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这一特征使得冠状病毒
比其他 RNA 病毒的
03:27
with a slower mutation rate,
than other RNA viruses.
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突变速度更加缓慢,
因此更加稳定。
03:31
While this may sound formidable,
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虽然这可能听上去很可怕,
03:33
the slow mutation rate
is actually a promising sign
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但是当涉及到削弱其致病性,
03:36
when it comes to disarming them.
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其缓慢的突变速率
实际上是一个很好的现象。
03:38
After an infection, our immune systems
can recognize germs
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在被感染以后,我们的
免疫系统可以识别病菌,
03:42
and destroy them more quickly
if they infect us again
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并且在它们再次感染我们时
快速地摧毁它们,
03:45
so they don’t make us sick.
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从而起到免疫效果。
03:47
But mutations can make a virus
less recognizable to our immune systems—
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但是突变会让病毒变得更不易
被我们的免疫系统察觉——
03:51
and therefore more difficult to fight off.
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因此也就更难去击溃它们。
03:53
They can also make antiviral drugs
and vaccines less effective,
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它们也会使抗病毒药品
和疫苗的效果大打折扣,
03:57
because they’re tailored
very specifically to a virus.
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因为这些药物都是
为每种病毒而特别定制的。
04:01
That’s why we need a new flu vaccine
every year—
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这就是为什么我们每年都
需要研发新的流感疫苗——
04:04
the influenza virus mutates so quickly
that new strains pop up constantly.
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因为流感病毒的突变发生得太快,
新株系会持续地出现。
04:09
The slower mutation rate
of coronaviruses means
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冠状病毒更慢的突变速率意味着
04:11
our immune systems, drugs,
and vaccines
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人体的免疫系统、药品以及疫苗
04:14
might be able to recognize them
for longer after infection,
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也许在感染之后的
更长时间内依然可以辨别它们,
04:18
and therefore protect us better.
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从而更好地保护我们的健康。
04:21
Still, we don’t know how long our bodies
remain immune to different coronaviruses.
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目前,我们还不知道被冠状病毒感染后,
人体的免疫时间能持续多久。
04:25
There’s never been an approved treatment
or vaccine for a coronavirus.
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对于冠状病毒,我们也尚未研发出
被证实有效的治疗方法或者疫苗。
04:29
We haven’t focused on treating
the ones that cause colds,
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我们还从未专注于应对
引起感冒的冠状病毒,
04:32
and though scientists began developing
treatments for SARS and MERS,
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虽然科学家们已经开始钻研
非典和中东呼吸综合征的治疗方法,
04:36
the epidemics ended before those
treatments completed clinical trials.
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但是疫情都在治疗方案
尚未完成临床实验时就结束了。
04:40
As we continue to encroach
on other animals’ habitats,
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随着我们继续不断侵占
其它动物的栖息地,
04:43
some scientists say a new coronavirus
jumping to humans is inevitable—
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科学家们宣称,新型冠状病毒
从动物传染给人类是无法避免的——
04:48
but if we investigate these unknowns,
it doesn’t have to be devastating.
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但如果我们调查清楚这些未知事物,
就可以避免大规模的破坏性后果。
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