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为什么新冠病毒具有如此强的传染性? – 译学馆
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为什么新冠病毒具有如此强的传染性?

Why Is This Virus So Contagious?

Thanks to Brilliant for supporting this episode of SciShow.
感谢Brilliant对本期《科学秀》的赞助
Go to Brilliant.org/SciShow to learn more about their course on Logic.
大家可前往Brilliant.org/SciShow学习更多逻辑思维课程
[♪ INTRO]
[前奏]
This episode was filmed on April 28th, 2020.
本期视频拍摄于2020年4月28日
If we have more recent episodes on COVID-19,
如果后续还有关于新冠肺炎的视频
we will include them in the description.
我们会把它们放在简介里
Scientists have learned a lot about the virus that causes COVID-19
自从几个月前发现导致新冠肺炎的病毒以来
since its discovery a few months ago,
科学家已经掌握了该病毒的大量信息
but one of the big lessons is that people with it are super contagious.
一个重要的发现是病毒携带者传染性很强
For instance, on April 7th,
比如 就在2020年4月7日
the US Centers for Disease Control published an analysis
美国疾控中心发布了一份分析报告说
which estimated that, on average,
据估计 平均来看
each person who caught the virus in Wuhan
在武汉 每个感染这种病毒的人
may have infected five to six other people.
可能传染了5至6人
That’s about twice the estimate for SARS back in the early 2000s.
这个估值是21世纪初SARS病毒的2倍
And, keep in mind that outbreaks grow exponentially, not linearly.
别忘了 疾病的爆发呈指数级增长 而非线性
So if one person with SARS infects three others,
如果1个携带了SARS病毒的人传染了3个人
and each of them infect three, and so on,
每个感染者又传染3个人 以此类推
after five rounds, the disease has spread to about 250 people.
五轮之后 大约会感染250人
But if a person with COVID-19 infects about six people,
而如果一个携带COVID-19病毒的人传染了6个人左右
who each infect five or six people, et cetera—
每个感染者又传染5或6人 以此类推
after those five rounds, more than 6000 people have caught it.
五轮之后 将有超6000人感染
We don’t know all the reasons this disease is so contagious.
我们还不完全清楚为何该病如此具有传染性
Researchers around the globe are still piecing together clues.
全球的科研人员还在梳理这些线索
But by comparing this new virus to the related virus that causes SARS,
通过比较这种新型病毒与导致SARS的同系病毒
they’ve found some promising leads—
他们发现了一些有价值的线索
and those leads might help us figure out how to actually beat this thing.
这些线索可能会帮我们找出能真正解决问题的方法
How contagious a disease is depends on a lot of things,
一种疾病的传染性取决于多种因素
and many of them overlap or interact.
许多因素又可叠加或相互影响
Like, we know that one big thing that makes the new coronavirus stand out
比如 我们知道一个重要的因素使得新冠病毒有个突出的特点
is that people can pass along the infection before they start showing symptoms.
就是患者出现症状前就具有传染性
This is what you might have seen referred to as presymptomatic transmission.
就是指你可能已经知道的“症状前传染性”
And with this virus, there also appears to be at least some asymptomatic transmission:
某些该病毒携带者甚至呈现了无症状传染性
people passing it along who never become sick themselves.
这些人本身不发病 但有传染性
For many diseases—including SARS—
许多疾病 包括SARS
those kinds of transmission just don’t happen.
不会出现这种无症状传染
The tricky part is explaining why.
这点解释起来不容易
The short answer is that those older diseases need relatively large droplets of fluid
简言之 原来的传染方式要借助更大的飞沫
from the airways to successfully leap into someone else—
直接从病人的呼吸道飞溅到另一个人身上
the kind only expelled by coughs or sneezes.
只需咳嗽或喷嚏就能产生这种类型的飞沫
Meanwhile, this new virus may be making the jump on smaller droplets,
但这种新病毒的传播可能只需更小的飞沫
like the ones made by talking or breathing.
例如在说话或呼吸过程中产生的小飞沫
And if that’s true, we’re not entirely sure how it pulls that off.
如果确实如此 我们就不太确定这个过程是怎么发生的
One possibility is that people who are infectious have a ton of virus particles in them,
一种可能性是被感染的人体内携带大量病毒
or a high viral load.
或者病毒载量很高
It’s basically a numbers game.
说到底 这就是一个数字游戏
If their throat and nose contain a lot of viruses,
如果患者喉咙及鼻腔有大量病毒
then even the smaller droplets they breathe out
那么呼出的飞沫即便比较小
could contain enough viruses to infect someone—
就含有足以感染他人的病毒量
or what epidemiologists call the infectious dose.
流行病学家称之为感染剂量
Now, you might think you’d know if your body is chock full of viruses—
你可能想知道你的体内病毒量是否很高
you’d assume you’d have, like, symptoms.
你会认为自己会出现对应的症状
But that’s not necessarily the case here.
但这次症状并不一定能作为判断的依据
With many respiratory viruses, including the original SARS,
很多呼吸道病毒 包括之前的SARS病毒
the symptoms actually come from your immune system’s reaction
其导致的症状主要是免疫系统的应答引起的
rather than the virus itself.
而非病毒本身
And researchers are finding that people with COVID-19
研究者发现 感染了新冠肺炎的人
can have really high viral loads even though they aren’t super sick.
即便病情不严重 病毒载量也很高
In fact, the timing of peak viral load,
事实上 病毒载量的峰值
especially in the nose and throat,
尤其是在鼻腔和喉咙里的
seems to be really early on,
似乎出现得相当早
like around or even before the onset of symptoms.
该病毒载量峰值在症状出现之时 甚至之前就显现了
That’s totally different than with SARS.
而这与SARS有很大区别
With that virus, peak viral load occurred about ten days
感染SARS病毒后 病毒载量的峰值期大概出现在
after people first showed symptoms.
首发症状的10天后
That suggests the COVID-19 virus can infect cells and replicate more quickly,
这表明新冠病毒感染细胞和复制的速度更快
or, in virology terms, it is a fitter virus.
或按病毒学术语 它可被称作一种烈性病毒
So, essentially, this virus is more efficient at virusing
所以从根本上说这种病毒的传播效率
than the original SARS.
比之前的SARS病毒更高
Which might seem strange since the two viruses are so alike.
这倒有些奇怪 因为两种病毒很相似
I mean, they even get into cells the exact same way.
我是说 它们入侵细胞的方式一模一样
Both hitch a ride in on protein on our cell membranes
都是靠搭载细胞膜上的蛋白
called angiotensin converting enzyme 2 or ACE2.
即血管紧张素转化酶2 或简称ACE2
Normally, these enzymes play a big role in maintaining blood pressure,
通常这种酶在维持血压方面发挥着重要作用
so they’re found on a lot of cells,
它们也存在于多种细胞上
especially ones in your respiratory system.
尤其是呼吸系统的细胞
And both viruses use a specific protein to grab onto ACE2.
两种病毒都靠一种特异性蛋白连接ACE2
It’s called the spike protein
这种蛋白称为棘突蛋白
because, well, it looks like a spike sticking out of the surface of the virus.
因为它看起来像病毒表面凸起的一根刺
But what differs between the SARS virus, SARS-CoV-1, and this virus
但SARS病毒(SARS-CoV-1) 与新冠病毒(SARS-CoV-2)的区别
is how well they stick to ACE2.
在于与ACE2的亲合力不同
Researchers estimate that this newer coronavirus binds
研究人员估计这种新型冠状病毒
ten times more tightly to human ACE2s.
与人类ACE2蛋白的亲合力比前者高10倍
And that’s probably because it has a number of changes
可能因为与酶连接的棘突部分
to the part of the spike that actually binds with the enzyme.
有了很大的变化
In fact, about half of the amino acids in this particular region
实际上 在这两种病毒的这个区域中
differ between the two viruses.
有大概一半的氨基酸都彼此不同
This matters because the better a virus is at binding to its receptor,
这点很重要 因为病毒与受体的亲合力越高
the fewer viruses you need to infect a cell.
感染细胞所需的病毒就越少
And ultimately, that may mean the infectious dose
最终可能意味着新冠病毒
is actually lower for this virus than SARS
实际上比SARS病毒
or other respiratory viruses.
或其它呼吸道病毒的感染剂量要低
If so, that could also help explain
如此便能解释
why people can spread this virus before they’re really ill,
为何人们在发病前就能传播新冠病毒
and why it can travel in smaller droplets.
以及细小飞沫能传播病毒的原因
It’s back to that numbers game—
回到病毒载量的问题上来
if it takes fewer viruses to infect someone,
如果只需少量病毒就能感染一个人
then even small exposures to the virus are more likely to get someone sick.
那即使暴露在少量病毒中 那人也可能被感染
But there may also be other things helping to lower the infectious dose, too.
而其它因素也可能降低感染剂量
Like, there’s a small chunk added to the spike protein
比如 棘突蛋白上连接的一种小片段
that experts think might make it more infection-ready from the get-go.
专家们认为这让病毒一开始就具备传染性
In other viruses, similar additions seem to make them more dangerous.
其它病毒中类似的小片段也使前者更加危险
So this is one of the leads scientists are eagerly following up on
所以科学家们正密切跟进这其中的一条线索
to figure out how this virus spreads so easily.
以弄清该病毒的传染性为何如此强
Even still, the infectious dose is just part of the story.
当然 感染剂量只是其中一个问题
To fully understand why this virus can replicate so well,
要完全弄清这个病毒能快速复制的原因
scientists also need to understand everything that happens
科学家们还需了解病毒进入细胞后
after it’s pulled into the cell.
进行的一切活动
So far, what’s clear is that, like other coronaviruses,
目前清楚的是 与其它冠状病毒一样
this virus hijacks a process called endocytosis.
新冠病毒利用了细胞的内吞作用
This is when a cell’s membrane folds inward, creating a little bubble
即 细胞膜向内凹陷 形成一个小泡
that carries in proteins and other stuff it can digest for parts.
包裹蛋白质和其他可消化成片段的物质
SARS-CoV-2 can hitch a ride in these bubbles
新冠病毒就搭了这趟“小泡顺风车”
and use them as a one-way ticket to the cell’s protein factories.
把其当作进入胞内蛋白加工厂的单程票
Then, instead of being digested, it breaks out—
然后 它没被消化 反而开始
putting its genome right where it will be translated and copied to make new viruses.
在它将被翻译和复制的地方释放基因组生产后代
It’s possible the new coronavirus can do all this more efficiently than other viruses—
可能新冠病毒的这种能力比其他病毒更强
at least, it seems to in some cultured cells.
至少 从一些培养的细胞中来看是的
That could help explain how it’s able to copy itself so quickly.
这也能解释为什么它复制得如此之快
But again, this is more of a lead than a conclusion at this point.
不过 此时这点应该作为线索但还非结论
Finally, if all that’s not enough,
最后还有一点
the new virus might replicate faster
新冠病毒还能复制得更快
and spread from people who aren’t sick
并且从没有生病的人身上传播开来
because it’s also better at evading the immune system.
因为它更擅长逃脱免疫系统的攻击
For example, its spike protein has extra binding sites for sugars
举个例子 其棘突蛋白的其余位点能结合糖
which could help “hide” important parts
这样能遮住
that the immune system would normally recognize.
那些免疫系统常规识别的重要部位
But also, the virus’s genome contains the blueprints for about two dozen proteins
但这个病毒的基因组包含了大约24种蛋白质的遗传型板
that aren’t directly involved in building new viruses.
这些蛋白质不会直接参与复制新病毒
Many of these probably help it dodge the cell’s virus detectors
而大部分很有可能能帮助病毒躲避细胞的监视
—but we don’t know a whole lot about them yet.
但我们对此还不太了解
What we do know is that there are nearly 400 specific differences
我们已经知道的是SARS病毒与新冠病毒
between the proteins of SARS-CoV-1 and SARS-CoV-2,
存在将近400个明确不同的区域
most of which are in these other proteins.
这些区域主要都存在于这些蛋白内
So there’s a lot more to look at.
所以还有很多有待研究
So, we don’t know all of the reasons this virus is so contagious.
我们还不完全清楚为何它的传染性如此强
But we do know enough to follow up on some promising leads.
但一些有价值的线索足以推进下一步研究
And doing that won’t just help answer the question in the title of this video.
这些研究不仅能回答本视频标题中的问题
It’ll also help doctors hunt down the most effective treatments
还能帮助医生找到最有效的治疗方案
and point researchers towards the best vaccine targets.
并为研究人员指明最佳的疫苗靶点
So, really, understanding what makes this virus so infectious
所以说真的 了解新冠病毒感染性强的原因
will help us figure out how best to defeat it.
能帮助我们找出击败它的最佳方法
One way to sharpen the reasoning skills that get us to answers is to study logic.
学习逻辑思维有助于提升推理能力得出答案
Because that’s not just something for Mr. Spock to go on about —
不仅仅是因为“金主爸爸”要求
it’s a whole discipline that forms the basis for mathematical reasoning.
而且那真的是一门助力形成数学思维的课程
Brilliant offers an introductory course on logic,
Brilliant为你提供了入门级的逻辑思维课程
and if you like it, you can also take Logic part II.
如果你喜欢 可以学习该课程的第二部分
Brilliant’s courses in math, computer science, engineering, and more
Brilliant的数学 计算机科学 工程学等课程
all aim to help you hone your scientific thinking skills.
旨在帮助你提升科学思维能力
So if you’re interested in sharpening your mind,
如果你有兴趣提升思维能力
the first 200 people to sign up at Brilliant.org/SciShow
头200位在Brilliant.org/SciShow注册的用户
will get 20% off the annual Premium subscription.
订阅的附加年费有8折优惠
[♪ OUTRO]
[尾声]

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视频概述

今年,新冠病毒肆虐全球,不禁让人想起了2003年的SARS。那你知道新冠病毒为何传染力这么强,它与SARS病毒有何异同吗?快来看看吧!

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