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Stated Clearly
Where Do New Viruses Come From
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What is Corona Virus? How do viruses spread? This animation explains the COVID virus came about and was able to spread from host to host and create a global pandemic.
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Video Transcript
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building copies of the virus instead of performing its normal tasks. Coronaviruses
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are a huge family of virus species that infect animal cells. Some
2:50
infect chickens, others infect pigs, some infect humans but most of them are
2:55
extremely mild. They simply give you the common cold. "Corona" means crown and
3:03
refers to the unusually large crown like spikes sticking out of their membranes.
3:07
These protein spikes are selectively sticky, sort of like velcro.
3:11
They don't attach to most objects but are extremely sticky when they bump into
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specific molecules found on the outsides of animal cells. Once held firmly in
3:22
place, the corona virus waits until swallowed by the cell. It then begins to
3:27
reproduce at the cells expense. Different animal species have different types of
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molecules on the outsides of their cells. Because of this, bird infecting corona
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viruses usually can't infect humans, their "Velcro" doesn't hold strong enough
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to our cells. Unfortunately the natural process of
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evolution can sometimes help a virus overcome this problem. When virus genes
3:53
are being copied during reproduction, mutations can occur. These are either due
3:58
to simple copying errors, or processes called reassortment and recombination.
4:03
These happen when two or more viruses infect a single cell. In most cases
4:08
mutations that change the shape of viral spikes render the virus useless. There
4:14
velcro no longer sticks to any host cells. On rare occasions, however, a chance
4:20
mutation will just happen to allow a virus to attach to a new host species. If
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the modified virus is then lucky enough to encounter that new host species,
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infection can occur. We call this a "spillover infection". The virus has
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spilled over into a new type of host. Early on during a spillover event the
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virus usually isn't very good at infecting its new host. It's velcro is
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not a perfect match and many other challenges might slow the virus down.
4:50
Oftentimes the mutations that let it infect the new host also make it worse
4:55
at infecting its original host. Because of this, many spillover viruses go
5:00
extinct after infecting just one or two people,
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they're usually dead ends. That said if the virus can survive and reproduce just
5:09
long enough, natural selection will promote any new mutations that help it
5:14
better spread and reproduce in the new host population. Positive mutations
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accumulate over multiple generations, negative mutations are discarded until...
5:24
BAM! A new epidemic is being screamed about on the news. Though it may seem to
5:31
us that these new viruses just sort of pop into existence overnight, scientists
5:36
now know there is a long slow burn before each explosion. Genetic evidence
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tells us that slowly evolving spill overs have been the cause of almost
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every major outbreak known in history. In the early 2000s, a coronavirus that used
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to only infect bats, appears to have spilled over into civets. There it
5:57
mutated even further and spilled over into humans. We called it the SARS virus
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because it causes Severe Acute Respiratory Syndrome. It spread
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internationally from person to person and several scientists were infected in
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the lab. By the time the virus was contained, over 8,000 people had been
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infected, over 700 died. A coronavirus from camels also recently spilled over
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to humans causing even more deaths. Coronaviruses are not the only types of
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animal viruses that can adapt to new hosts. HIV spilled over from chimps, most
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likely when someone cut themselves while preparing chimp meat for dinner.
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The swine flu came partly from pigs but we think it actually
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evolved through a recombination with a pig virus and a bird virus. The 1918
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Spanish flu, the big one that devastated populations all around the world, may
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have spilled over from chickens! While the evidence is not yet conclusive, the new
6:58
coronavirus might just be one more example of normal evolution. A very
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similar virus has been found in bats and another was recently discovered in
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pangolins. These animals are endangered, they're protected, but they're often used
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illegally for food, rituals, and alternative medicine in the region where
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COVID-19 first broke out. Now, there are serious people checking to make sure
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that the virus did not come from a lab, either by accident or on purpose. After all,
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the technology to genetically modified viruses really does exist, but
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it's important to understand that the normal process of descent with
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modification acted upon by natural selection really does produce new
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viruses. It happens naturally. The chance of a virus evolving to successfully
