Q-Eng

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コロナウイルスとはウイルスの分類の一つ。 コロナは数百種あり人に感染するのが７種｡
うち４種はよくある風邪で感染力が強い。２種は凶暴なSARS､MERSだがすぐに収束した｡
７番目が新型コロナ Covid-19 で強い感染力と高い致死率を併せ持った。
（注 ： 約３年後、弱毒化し2023年５月にインフル並みの５類となった）

中　５分　140wpm　　　　　　　　　　　　　　　　　　　　　　　2020年5月　　　　　　　　　　　　　　　　　　　　 　　　　　　 　　　　

字幕 ： 開始後 で字幕On/Off､ で言語選択。文字の色やサイズﾞはｵﾌﾟｼｮﾝから｡
.　　　　 動画を見るとき、 でフルスクリーンに拡大すると見やすい。

★下記英文は ポップアップ辞書 が使えます｡
　　テキストはこちら⇒英日トランスクリプト （字幕はYouTubeの方が大きく見やすい）　　　　　 　　　　　　 　　

For almost a decade, scientists chased the source of a deadly new virus through China’s tallest mountains and most isolated caverns. They finally found it here: in the bats of Shitou Cave（石头洞）. The virus in question was a coronavirus that caused an epidemic of severe acute respiratory syndrome, or SARS, in 2003.

Coronaviruses are a group of viruses covered in little protein spikes that look like a crown— or "corona" in Latin. There are hundreds of known coronaviruses.
Seven of them infect humans, and can cause disease. The coronavirus SARS-CoV causes SARS, MERS-CoV causes MERS, and SARS-CoV-2 causes the disease COVID-19.

Of the seven human coronaviruses, four cause colds, mild, highly contagious（伝染性の） infections of the nose and throat. Two infect the lungs, and cause much more severe illnesses. The seventh, which causes COVID-19, has features of each: it spreads easily, but can severely impact the lungs.

When an infected person coughs, droplets containing the virus spray out. The virus can infect a new person when the droplets enter their nose or mouth. Coronaviruses transmit best in enclosed spaces, where people are close together.

Cold weather keeps their delicate casing from drying out, enabling the virus to survive for longer between hosts, while UV exposure from sunlight may damage it. These seasonal variations matter more for established viruses.

But because no one is yet immune to a new virus, it has so many potential hosts that it doesn’t need ideal conditions to spread. In the body, the protein spikes embed in the host’s cells and fuse with them— enabling the virus to hijack the host cell’s machinery to replicate its own genes.

Coronaviruses store their genes on RNA. All viruses are either RNA viruses or DNA viruses. RNA viruses tend to be smaller, with fewer genes, meaning they infect many hosts and replicate quickly in those hosts. In general, RNA viruses don’t have a proofreading（校正） mechanism, whereas DNA viruses do.

So when an RNA virus replicates, it’s much more likely to have mistakes called mutations（変異株）. Many of these mutations are useless or even harmful. But some make the virus better suited for certain environments— like a new host species.

Epidemics often occur when a virus jumps from animals to humans. This is true of the RNA viruses that caused the Ebola, Zika, and SARS epidemics, and the COVID-19 pandemic. Once in humans, the virus still mutates— usually not enough to create a new virus, but enough to create variations, or strains, of the original one. Coronaviruses have a few key differences from most RNA viruses.

They’re some of the largest, meaning they have the most genes. That creates more opportunity for harmful mutations. To counteract this risk, coronaviruses have a unique feature: an enzyme（酵素） that checks for replication errors and corrects mistakes. This makes coronaviruses much more stable, with a slower mutation rate, than other RNA viruses.

While this may sound formidable, the slow mutation rate is actually a promising sign when it comes to disarming them. After an infection, our immune systems can recognize germs and destroy them more quickly if they infect us again so they don’t make us sick. But mutations can make a virus less recognizable to our immune systems— and therefore more difficult to fight off.

They can also make antiviral drugs and vaccines less effective, because they’re tailored very specifically to a virus. That’s why we need a new flu vaccine every year— the influenza virus mutates so quickly that new strains pop up constantly.

The slower mutation rate of coronaviruses means our immune systems, drugs, and vaccines might be able to recognize them for longer after infection, and therefore protect us better. Still, we don’t know how long our bodies remain immune to different coronaviruses.

There’s never been an approved treatment or vaccine for a coronavirus. We haven’t focused on treating the ones that cause colds, and though scientists began developing treatments for SARS and MERS, the epidemics ended before those treatments completed clinical trials.
　注 ： 2021年以降 強力なワクチンが実用化され世界中で使用された。
　　　　 しかし 2024年2月現在、インフルのような特効薬はない。

As we continue to encroach（侵入する） on other animals’ habitats, some scientists say a new coronavirus jumping to humans is inevitable— but if we investigate these unknowns, it doesn’t have to be devastating.
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