What is a coronavirus?

For almost a decade, scientists chased the source of a deadly new virus through china’s tallest mountains and most isolated caverns洞穴.
They finally founded it here: in the bats蝙蝠 of Shitou Cave.
The virus in question was a coronavirus that caused an epidemic of severe acute respiratory syndrome 急性呼吸綜合征, or SARS, in 2003.

Coronaviruses are a group of virus covered in little protein spikes that look like a crown— or "corona" in Latin.
There are handreds of known coronaviruses.
Seven of them infect humans, and can cause disease.
The coronavirus SARS CoV causes SARS, MARS-CoV causes MERS, and SARS-CoV-2 causes COVID-19.
Of the 7 human coronaviruses, 4 causes colds, mild輕度, highly contagious傳染性 infections of the nose and throat.
Two infects the lungs, and causes much more sevever illnesses.
The 7th, which causes CODIV-19, has feathers of each: it spreads easily, but can severely impact the lungs.

When an infected person coughs, droplets containing the virus spray噴霧 out.
The virus and infect a new person when the droplets enter their nose or mouth.
Coronavirus transmit best in enclosed spaces, where people are close together.
Cold weather keeps their delicate細(xì)膩的 casing from drying out, enabling the virus to survive for longer between hosts, while UV exposure from sunlight may damage it.
These seasonal variations mater 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尖峰 embed in the host’s cells and fuse with them- enabling the virus to hijack劫持 the host cell’s machinery to replicate復(fù)制 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 few genes, meaning they infect many hosts and replicate quickly in those hosts.
In general RNA viruses don’t have a proofreading校對 mechanism機(jī)制, whereas DNA viruses do.
So when an RNA virus replicates, it’s much more likely to have mistakes called mutations突變.
Many of these mutations are useless or even harmful. But some make the virus better suited for certain environments- like a new host species種類.

Epidemics流行病 often occur when a virus from 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大流行.
Once in humans, the virus still mutates- usally not enough to create a new virus, but enough to create variations, or strains毒株, of the original one.
Coronavirus have a few key differences from most RNA VIRUSES.
They’re some of the largest, meaning they have more genes.
That creates more opportunity for harmful mutations.
To counteract抵消 this risk, coronavirus have a unique feature: an enzyme that checks for replication errors and corrects mistakes.
While this may sound formidable強(qiáng)大, the slow mutation rate is actually a promising sign when it comes to disarming解除武裝 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抗病毒物質(zhì) drugs and vaccines疫苗 less effective, because they’re tailored量身定制 very specifically to a virus.
That’s why we need a new flu vaccine every year— the influenza流感 virus mutates so quickly that new strains毒株 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.

As we continue to encroach侵犯 on other animals’ habitats, some scientists say a new coronavirus jumping to humans is inevitable必然— but if we investigate調(diào)查 these unknowns, it doesn’t have to be devastating毀滅性的.