What is a coronavirus? - Elizabeth Cox

譯者: Lilian Chiu 審譯者: Helen Chang

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

科學家花了近十年的時間 在尋找一種新型致命病毒的來源，

through China’s tallest mountains and most isolated caverns.

一路追到中國最高的山岳 及最偏遠的洞穴。

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

他們終於在石頭洞中的 蝙蝠身上找到了這種病毒：

The virus in question was a coronavirus

前面提到的病毒是種冠狀病毒，

that caused an epidemic of severe acute respiratory syndrome,

在 2003 年，這種病毒造成了

嚴重急性呼吸道症候群 （SARS）的流行。

or SARS, in 2003.

Coronaviruses are a group of viruses

冠狀病毒這種病毒

covered in little protein spikes that look like a crown—

上面蓋著小型蛋白質突刺， 看起來像皇冠一樣——

or "corona" in Latin.

拉丁文叫「corona」。

There are hundreds of known coronaviruses.

已知的冠狀病毒就有數百種。

Seven of them infect humans, and can cause disease.

當中有七種會感染人類 且可能會造成疾病。

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

SARS 冠狀病毒會造成 SARS、

MERS 冠狀病毒會造成 MERS，

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

而新型冠狀病毒會造成嚴重特殊 傳染性肺炎（COVID-19）。

Of the seven human coronaviruses, four cause colds,

七種會感染人類的冠狀病毒中， 有四種會造成感冒，

mild, highly contagious infections of the nose and throat.

鼻子和喉嚨會有 輕微但傳染力強的感染。

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

兩種則會感染肺部， 導致更嚴重的疾病。

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

造成 COVID-19 的第七種 則具有每一種特徵：

it spreads easily, but can severely impact the lungs.

它很容易傳播，也會嚴重影響肺部。

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

當受感染的人咳嗽時， 含有病毒的飛沫就會灑出去。

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

當飛沫進入另一個人的口鼻時， 就可能會感染這個人。

Coronaviruses transmit best in enclosed spaces,

人與人很靠近的密閉空間

是最適合冠狀病毒傳播的環境。

where people are close together.

Cold weather keeps their delicate casing from drying out,

天冷時，病毒脆弱的外殼 較不易被破壞，

enabling the virus to survive for longer between hosts,

使其存活於宿主的時間更長，

while UV exposure from sunlight may damage it.

若暴露在太陽光的紫外線下， 外殼就可能受損。

These seasonal variations matter more for established viruses.

對於已知的病毒， 這些季節性變化的影響較大。

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

但因為還沒有人對新病毒有免疫力，

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

可感染的宿主非常多， 不用理想的條件也會傳播出去。

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

在體內，蛋白質突刺 會插進宿主的細胞中，

和細胞融合在一起——

enabling the virus to hijack the host cell’s machinery

使病毒得以劫持宿主細胞 以複製自身的基因。

to replicate its own genes.

Coronaviruses store their genes on RNA.

冠狀病毒的基因儲存在 RNA 上。

All viruses are either RNA viruses or DNA viruses.

所有的病毒若不是 RNA 病毒就是 DNA 病毒。

RNA viruses tend to be smaller, with fewer genes,

RNA 病毒通常比較小，基因數也較少，

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

那表示它們會感染許多宿主， 並在那些宿主體內快速複製。

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

一般來說，RNA 病毒 沒有校對的機制，

whereas DNA viruses do.

DNA 病毒則有。

So when an RNA virus replicates,

所以 RNA 病毒在複製時

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

更有可能會出錯，稱為突變。

Many of these mutations are useless or even harmful.

有許多突變是無用的， 甚至是有害的。

But some make the virus better suited for certain environments—

但有些突變會讓病毒 更適應某些環境——

like a new host species.

比如新的寄宿對象物種。

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

倘若病毒從動物跳到人類身上， 通常就會發生傳染病的流行。

This is true of the RNA viruses that caused

造成伊波拉、茲卡、SARS 流行，

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

及 COVID-19 全球大流行的 RNA 病毒皆是如此。

Once in humans, the virus still mutates—

病毒到人類身上後仍會突變——

usually not enough to create a new virus,

通常不足以造出新病毒，

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

但足以造出原始病毒的變異或分型。

Coronaviruses have a few key differences from most RNA viruses.

冠狀病毒和大部分 RNA 病毒 有幾個關鍵性的差異：

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

它們尺寸大，也就是基因數目多，

That creates more opportunity for harmful mutations.

讓它們更有機會發生有害的突變。

To counteract this risk, coronaviruses have a unique feature:

為了降低這種風險， 冠狀病毒有個獨特的特徵：

an enzyme that checks for replication errors and corrects mistakes.

它有種負責檢查並修正 複製錯誤的酵素。

This makes coronaviruses much more stable,

這個特徵讓冠狀病毒更加穩定，

with a slower mutation rate, than other RNA viruses.

突變的速度比其他 RNA 病毒慢。

While this may sound formidable,

雖然可能這聽起來相當難搞，

the slow mutation rate is actually a promising sign

然而緩慢的突變率實際上是 有希望解除病毒武裝的信號。

when it comes to disarming them.

After an infection, our immune systems can recognize germs

在受感染後，我們的 免疫系統便會認得病菌，

and destroy them more quickly if they infect us again

再次受到它們感染時， 就會快速摧毀它們，

so they don’t make us sick.

避免我們生病。

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

但病毒突變後會比較難 被我們的免疫系統認出來——

and therefore more difficult to fight off.

因此較難對抗它們。

They can also make antiviral drugs and vaccines less effective,

突變也減低抗病毒藥物 和疫苗的效果。

because they’re tailored very specifically to a virus.

因為這些藥物和疫苗都 明確針對某種病毒量身打造，

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

因此我們每年都需要新的流感疫苗。

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

流感疫苗的突變非常快， 經常會有新的分型出現。

The slower mutation rate of coronaviruses means

冠狀病毒的突變速率較慢，

our immune systems, drugs, and vaccines

表示我們的免疫系統、藥物、疫苗

might be able to recognize them for longer after infection,

在受感染後較長的一段時間內 都還能認得這些病毒，

and therefore protect us better.

因此我們能受到較佳的保護。

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

但我們仍然不清楚我們的身體 對不同的冠狀病毒能免疫多久。

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

尚未有任何證明有效的治療方式 或疫苗可以對付冠狀病毒。

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

一直以來我們並未著重治療 造成感冒的冠狀病毒，

and though scientists began developing treatments for SARS and MERS,

雖然科學家針對 SARS 及 MERS 開發治療方式，

the epidemics ended before those treatments completed clinical trials.

但在完成臨床試驗前 疫情就已經告終了。

As we continue to encroach on other animals’ habitats,

有些科學家說，只要我們 繼續侵犯其他動物的棲息地，

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

就一定會有新的冠狀病毒 跳到人類身上。

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

但若我們研究這些未知的領域， 結果不見得會這麼慘痛。