What is a coronavirus? - Elizabeth Cox

翻译人员: Ethan Huang 校对人员: Yolanda Zhang

For almost a decade, scientists chased the source of a deadly new virus

在近十年间，从中国的 最高峰到最偏远的洞穴里，

through China’s tallest mountains and most isolated caverns.

科学家们一直在追寻一种 新型致命病毒的源头。

They finally found it here: in the bats of Shitou Cave.

他们最终在“石头洞”的蝙蝠 身上找到了答案。

The virus in question was a coronavirus

人们所找寻的病毒是 一种在 2003 年引发了

that caused an epidemic of severe acute respiratory syndrome,

严重急性呼吸系统 综合症流行病，

or SARS, in 2003.

简称非典型肺炎（SARS）的冠状病毒。

Coronaviruses are a group of viruses

冠状病毒是一群表面有着 棘突蛋白的病毒，

covered in little protein spikes that look like a crown—

看起来很像皇冠——

or "corona" in Latin.

在拉丁文中意为“冠状物”。

There are hundreds of known coronaviruses.

目前已知的冠状病毒有数百种。

Seven of them infect humans, and can cause disease.

其中的七种可以传染给人类 并且引起疾病。

The coronavirus SARS-CoV causes SARS, MERS-CoV causes MERS,

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，

and SARS-CoV-2 causes the disease COVID-19.

而 SARS-CoV-2 则可引起 新型冠状病毒肺炎（COVID-19）。

Of the seven human coronaviruses, four cause colds,

七种会感染人类的冠状病毒中， 有四种会导致感冒，

mild, highly contagious infections of the nose and throat.

即症状温和 且具有高传染性的鼻喉感染。

Two infect the lungs, and cause much more severe illnesses.

有两种会感染肺部并且 引起更严重的疾病。

The seventh, which causes COVID-19, has features of each:

引起 COVID-19 的第七种病毒 综合了上述两类的特征：

it spreads easily, but can severely impact the lungs.

不仅极易传播， 而且会严重地影响肺部。

When an infected person coughs, droplets containing the virus spray out.

当受感染者咳嗽时，含有病毒 的飞沫就会喷溅而出。

The virus can infect a new person when the droplets enter their nose or mouth.

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。

Coronaviruses transmit best in enclosed spaces,

冠状病毒在封闭的 空间内最易传播，

where people are close together.

在这些地方人与人之间距离很近。

Cold weather keeps their delicate casing from drying out,

寒冷的天气可以防止病毒的 精密外壳变干，

enabling the virus to survive for longer between hosts,

使得它们在宿主之间 传播时能够存活更长时间。

while UV exposure from sunlight may damage it.

但是紫外线的照射 可能会消灭它们。

These seasonal variations matter more for established viruses.

这些季节上的变化对于 已经存在的病毒影响更大。

But because no one is yet immune to a new virus,

但是因为至今没有任何人 对新出现的病毒免疫，

it has so many potential hosts that it doesn’t need ideal conditions to spread.

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。

In the body, the protein spikes embed in the host’s cells and fuse with them—

进入人体后，棘突蛋白会嵌入 宿主的细胞内并与它们融合——

enabling the virus to hijack the host cell’s machinery

这个过程让病毒能够控制 宿主细胞的运转体系，

to replicate its own genes.

以复制其自身的遗传基因。

Coronaviruses store their genes on RNA.

冠状病毒把它们的基因 储存在 RNA 内。

All viruses are either RNA viruses or DNA viruses.

所有病毒都是 RNA 或者 DNA 病毒。

RNA viruses tend to be smaller, with fewer genes,

RNA 病毒通常更小， 携带更少的基因，

meaning they infect many hosts and replicate quickly in those hosts.

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。

In general, RNA viruses don’t have a proofreading mechanism,

一般来说，RNA 病毒没有校对机制，

whereas DNA viruses do.

而 DNA 病毒则有。

So when an RNA virus replicates,

因此，当 RNA 病毒进行自我复制时，

it’s much more likely to have mistakes called mutations.

更有可能发生错误，即所谓的“突变”。

Many of these mutations are useless or even harmful.

大多数的突变都是对其自身 无用，甚至是无益的。

But some make the virus better suited for certain environments—

但是有一些变异可以帮助病毒 更加适应某些特定的环境——

like a new host species.

比如说新的宿主物种。

Epidemics often occur when a virus jumps from animals to humans.

传染病通常在病毒从动物 传染到人类时出现，

This is true of the RNA viruses that caused

比如由 RNA 病毒导致的

the Ebola, Zika, and SARS epidemics, and the COVID-19 pandemic.

埃博拉、寨卡和非典传染病，以及 COVID-19 全球性大流行病。

Once in humans, the virus still mutates—

进入人体以后， 病毒仍然会发生突变——

usually not enough to create a new virus,

虽然这种突变不足以 创造新型的病毒，

but enough to create variations, or strains, of the original one.

但足以使原本的病毒 产生变化，或产生新株系。

Coronaviruses have a few key differences from most RNA viruses.

相比大多数 RNA 病毒， 冠状病毒有几个主要的差别。

They’re some of the largest, meaning they have the most genes.

它们是体积最大的 RNA 病毒， 有着最多的遗传基因，

That creates more opportunity for harmful mutations.

也就更可能出现 对自身有害的变异。

To counteract this risk, coronaviruses have a unique feature:

为了抵消这种风险，冠状病毒 展现出了一种独有的特性：

an enzyme that checks for replication errors and corrects mistakes.

一种可以检验基因复制错误 并进行纠正的酶。

This makes coronaviruses much more stable,

这一特征使得冠状病毒 比其他 RNA 病毒的

with a slower mutation rate, than other RNA viruses.

突变速度更加缓慢， 因此更加稳定。

While this may sound formidable,

虽然这可能听上去很可怕，

the slow mutation rate is actually a promising sign

但是当涉及到削弱其致病性，

when it comes to disarming them.

其缓慢的突变速率 实际上是一个很好的现象。

After an infection, our immune systems can recognize germs

在被感染以后，我们的 免疫系统可以识别病菌，

and destroy them more quickly if they infect us again

并且在它们再次感染我们时 快速地摧毁它们，

so they don’t make us sick.

从而起到免疫效果。

But mutations can make a virus less recognizable to our immune systems—

但是突变会让病毒变得更不易 被我们的免疫系统察觉——

and therefore more difficult to fight off.

因此也就更难去击溃它们。

They can also make antiviral drugs and vaccines less effective,

它们也会使抗病毒药品 和疫苗的效果大打折扣，

because they’re tailored very specifically to a virus.

因为这些药物都是 为每种病毒而特别定制的。

That’s why we need a new flu vaccine every year—

这就是为什么我们每年都 需要研发新的流感疫苗——

the influenza virus mutates so quickly that new strains pop up constantly.

因为流感病毒的突变发生得太快， 新株系会持续地出现。

The slower mutation rate of coronaviruses means

冠状病毒更慢的突变速率意味着

our immune systems, drugs, and vaccines

人体的免疫系统、药品以及疫苗

might be able to recognize them for longer after infection,

也许在感染之后的 更长时间内依然可以辨别它们，

and therefore protect us better.

从而更好地保护我们的健康。

Still, we don’t know how long our bodies remain immune to different coronaviruses.

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。

There’s never been an approved treatment or vaccine for a coronavirus.

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。

We haven’t focused on treating the ones that cause colds,

我们还从未专注于应对 引起感冒的冠状病毒，

and though scientists began developing treatments for SARS and MERS,

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，

the epidemics ended before those treatments completed clinical trials.

但是疫情都在治疗方案 尚未完成临床实验时就结束了。

As we continue to encroach on other animals’ habitats,

随着我们继续不断侵占 其它动物的栖息地，

some scientists say a new coronavirus jumping to humans is inevitable—

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——

but if we investigate these unknowns, it doesn’t have to be devastating.

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。