Name: Where Do New Viruses Come From?
Uploaded: 2020-03-05T22:11:27.000Z
Duration: 10 min 10 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Basic passive voice

Stated Clearly is funded by our viewers on patreon.com/statedclearly

Stated Clearly presents: Where do new viruses come from? If you've been

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watching the news you've probably heard of the novel or new coronavirus which,

starting in late 2019, began making people ill in China. International air

travel has since allowed it to spread person-to-person to new countries. As

government's begin to issue travel restrictions and even quarantines

speculations about the origin of the virus began to spread online. Some claim

that the virus might be a genetically modified weapon but extraordinary claims

require extraordinary evidence. This claim currently seems highly

unlikely. Others suggest that the virus may be an escaped lab specimen. This

actually is possible, viruses have escaped from research labs in the past,

but as of the time that I'm recording this voice-over, investigations into this

idea have not yet reached any solid conclusions. Could there be another more

natural explanation for the origin of the virus? The answer is yes CPVOD-19

the new human-infecting coronavirus, may have simply evolved from an older animal-infecting

coronavirus. To understand how this may have happened let's first take

a look at viruses in general. What are viruses? Of the many things that can make

you sick by infecting and reproducing inside you, viruses are among the

smallest. If we resize this drawing to a more realistic scale you see that

hundreds of viruses can fit inside a single bacterial cell. That's how tiny

they are. Thousands of different viral species have been studied and described

by scientists so far, millions more likely exist. They come in many forms but

all species consists of a small collection of genes (stretches of either

DNA or RNA that carry information for making more copies of the virus) and

those genes are enclosed in a protective coating of protein and sometimes a lipid

membrane. All known viruses are parasitic but most are

not parasitic to humans. Instead some only target plant cells others only

infect bacteria and so on. A virus reproduces by getting its genes into a

living cell. Different viruses do this in different ways but once inside, the cell

acts as if the viral genes were its own genes. It begins reading them and

building copies of the virus instead of performing its normal tasks. Coronaviruses

are a huge family of virus species that infect animal cells. Some

infect chickens, others infect pigs, some infect humans but most of them are

extremely mild. They simply give you the common cold. "Corona" means crown and

refers to the unusually large crown like spikes sticking out of their membranes.

These protein spikes are selectively sticky, sort of like velcro.

They don't attach to most objects but are extremely sticky when they bump into

specific molecules found on the outsides of animal cells. Once held firmly in

place, the corona virus waits until swallowed by the cell. It then begins to

reproduce at the cells expense. Different animal species have different types of

molecules on the outsides of their cells. Because of this, bird infecting corona

viruses usually can't infect humans, their "Velcro" doesn't hold strong enough

to our cells. Unfortunately the natural process of

evolution can sometimes help a virus overcome this problem. When virus genes

are being copied during reproduction, mutations can occur. These are either due

to simple copying errors, or processes called reassortment and recombination.

These happen when two or more viruses infect a single cell. In most cases

mutations that change the shape of viral spikes render the virus useless. There

velcro no longer sticks to any host cells. On rare occasions, however, a chance

mutation will just happen to allow a virus to attach to a new host species. If

the modified virus is then lucky enough to encounter that new host species,

infection can occur. We call this a "spillover infection". The virus has

spilled over into a new type of host. Early on during a spillover event the

virus usually isn't very good at infecting its new host. It's velcro is

not a perfect match and many other challenges might slow the virus down.

Oftentimes the mutations that let it infect the new host also make it worse

at infecting its original host. Because of this, many spillover viruses go

extinct after infecting just one or two people,

they're usually dead ends. That said if the virus can survive and reproduce just

long enough, natural selection will promote any new mutations that help it

better spread and reproduce in the new host population. Positive mutations

accumulate over multiple generations, negative mutations are discarded until...

BAM! A new epidemic is being screamed about on the news. Though it may seem to

us that these new viruses just sort of pop into existence overnight, scientists

now know there is a long slow burn before each explosion. Genetic evidence

tells us that slowly evolving spill overs have been the cause of almost

every major outbreak known in history. In the early 2000s, a coronavirus that used

to only infect bats, appears to have spilled over into civets. There it

mutated even further and spilled over into humans. We called it the SARS virus

because it causes Severe Acute Respiratory Syndrome. It spread

internationally from person to person and several scientists were infected in

the lab. By the time the virus was contained, over 8,000 people had been

infected, over 700 died. A coronavirus from camels also recently spilled over

to humans causing even more deaths. Coronaviruses are not the only types of

animal viruses that can adapt to new hosts. HIV spilled over from chimps, most

likely when someone cut themselves while preparing chimp meat for dinner.

The swine flu came partly from pigs but we think it actually

evolved through a recombination with a pig virus and a bird virus. The 1918

Spanish flu, the big one that devastated populations all around the world, may

have spilled over from chickens! While the evidence is not yet conclusive, the new

coronavirus might just be one more example of normal evolution. A very

similar virus has been found in bats and another was recently discovered in

pangolins. These animals are endangered, they're protected, but they're often used

illegally for food, rituals, and alternative medicine in the region where

COVID-19 first broke out. Now, there are serious people checking to make sure

that the virus did not come from a lab, either by accident or on purpose. After all,

the technology to genetically modified viruses really does exist, but

it's important to understand that the normal process of descent with

modification acted upon by natural selection really does produce new

viruses. It happens naturally. The chance of a virus evolving to successfully

infect a new species is extremely low but there are over seven and a half

billion people on this planet, most of us interact with animals on a

daily basis. We keep them as pets, we eat them as food. This means that as unlikely

as spillover infections might be, there are billions of opportunities for one to

take hold every single day. Add this the fact that the entire world is now

connected through international flights, and you realize that what happens in

Vegas doesn't actually stay in Vegas, at least not the way that it used to.

Luckily we have international groups like the World Health Organization and

various centers for Disease Control to help contain outbreaks when they happen.

With international cooperation we have prevented many catastrophes in the past