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Thanks to Brilliant for supporting this episode of SciShow. Go to Brilliant.org/SciShow to learn more about their course on Logic.
感谢Brilliant对本期节目的支持。登陆Brilliant.org/SciShow了解更多逻辑课程信息。
This episode was filmed on April 28th, 2020. If we have more recent episodes on COVID-19, we will include them in the description.
本期视频拍摄于2020年4月28日。更多该系列视频将陆续推出。
Scientists have learned a lot about the virus that causes COVID-19 since its discovery a few months ago,
自从发现COVID-19以来，科学家们已经对该病毒有很多了解，
but one of the big lessons is that people with it are super contagious.
但其中一个重要的教训是，该病毒的感染者具有超强的传染性。
For instance, on April 7th, the US Centers for Disease Control published an analysis which estimated that, on average,
例如，4月7日，美国疾病控制中心分析估计，
each person who caught the virus in Wuhan may have infected five to six other people.
平均每位病人可感染5到6个人。
That's about twice the estimate for SARS back in the early 2000s. And, keep in mind that outbreaks grow exponentially, not linearly.
是2000年年初SARS病毒的约两倍。请记住，疫情爆发是呈指数增长的，而不是线性增长的。
So if one person with SARS infects three others, and each of them infect three, and so on, after five rounds, the disease has spread to about 250 people.
如果SARS患者感染3个人，每个感染者再感染3人，以此类推，5轮过后，该疾病已传染给了约250人。
But if a person with COVID-19 infects about six people, who each infect five or six people, et cetera—after those five rounds,
但如果COVID-19患者感染约6个人，每个感染者再传染给5到6个人，以此类推——5轮过后，
more than 6000 people have caught it. We don't know all the reasons this disease is so contagious.
就有超过6000人感染了该疾病。我们不知道这种疾病如此具有传染性的所有原因。
Researchers around the globe are still piecing together clues.
全球研究人员仍在拼凑线索。
But by comparing this new virus to the related virus that causes SARS,
通过将这种新病毒与导致SARS的相关病毒进行对比，
they've found some promising leads—and those leads might help us figure out how to actually beat this thing.
他们发现一些有希望的线索——这些线索或许可以帮助我们弄清楚如何真正对抗该病毒。
How contagious a disease is depends on a lot of things, and many of them overlap or interact.
一种疾病的传染性强度取决于很多方面，其中很多都是重合或相互作用的。
Like, we know that one big thing that makes the new coronavirus stand out is that people can pass along the infection before they start showing symptoms.
比如让新冠状病毒如此突出的一个方面是，人们可以在出现症状前传染该疾病。
This is what you might have seen referred to as presymptomatic transmission.
这就是大家可能听说过的所谓症状前传播。
And with this virus, there also appears to be at least some asymptomatic transmission: people passing it along who never become sick themselves.
而这种病毒，似乎也至少有一些无症状的传播：传播它的人自己没有生病。
For many diseases—including SARS—those kinds of transmission just don't happen. The tricky part is explaining why.
对很多疾病而言——包括SARA——是不会出现这种无症状传播的。最棘手的部分是解释原因。
The short answer is that those older diseases need relatively large droplets of fluid from the airways to successfully leap into someone else—
简而言之，那些较老的疾病需要相对较大的呼吸道液滴才能成功地传染给他人——
the kind only expelled by coughs or sneezes. Meanwhile, this new virus may be making the jump on smaller droplets,
只有咳嗽或打喷嚏时才会排出较大的呼吸道液滴。与此同时，这种新病毒可能在更小的飞沫上跳跃，
like the ones made by talking or breathing. And if that's true, we're not entirely sure how it pulls that off.
比如说话或呼吸产生的飞沫。如果这是真的，我们并不完全确定它是如何做到的。
One possibility is that people who are infectious have a ton of virus particles in them, or a high viral load.
一种可能性是感染者携带大量病毒颗粒，或有很高的病毒载量。
It's basically a numbers game. If their throat and nose contain a lot of viruses,
这基本上是一个数字游戏。如果他们的咽喉和鼻子中携带大量病毒，
then even the smaller droplets they breathe out could contain enough viruses to infect someone or what epidemiologists call the infectious dose.
那么即便是他们呼吸出的较小滴液都可能携带足量的病毒，以感染别人或流行病学家所谓的感染剂量。
Now, you might think you'd know if your body is chock full of viruses—you'd assume you'd have, like, symptoms.
现在你可能会认为，如果你的身体携带病毒，你是能够知道的——你以为你会出现症状。
But that's not necessarily the case here. With many respiratory viruses, including the original SARS,
但是这种病毒不是这样的。包括原SARS在内的很多呼吸道病毒
the symptoms actually come from your immune system's reaction rather than the virus itself.
其症状实际上来自于你的免疫系统的反应，而不是病毒本身。
And researchers are finding that people with COVID-19 can have really high viral loads even though they aren't super sick.
研究人员发现，COVID-19患者的病毒载量非常高，即使他们病得并不严重。
In fact, the timing of peak viral load, especially in the nose and throat, seems to be really early on, like around or even before the onset of symptoms.
实际上，病毒载量峰值的时间，尤其是在鼻子和喉咙里的，似乎是非常早的，就像在症状出现之前。
That's totally different than with SARS. With that virus, peak viral load occurred about ten days after people first showed symptoms.
这和SARS完全不同。患者首次出现症状后10天左右，病毒载量达到峰值。
That suggests the COVID-19 virus can infect cells and replicate more quickly—or, in virology terms, it is a fitter virus.
这表明COVID-19病毒可以感染细胞并更快地复制——或者，用病毒学术语来说，它是一种更合适的病毒。
So, essentially, this virus is more efficient at virusing than the original SARS. Which might seem strange since the two viruses are so alike.
所以这种病毒在传播方面比SARS更高效。这或许看似很奇怪，因为这两种病毒非常相似。
I mean, they even get into cells the exact same way.
我的意思是，它们甚至以完全相同的方式进入细胞。
