El coronavirus no fue diseñado en un laboratorio.
Así es como lo sabemos.
The coronavirus was not engineered in a lab. Here's how we know.
Mitos para dejar en cuarentena
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Editor's note: On April 16, news came
out that the U.S. government said it was investigating the possibility
that the novel coronavirus may have somehow escaped from a lab, though
experts still think the possibility that it was engineered is unlikely.
This Live Science report explores the origin of SARS-CoV-2.
As the novel coronavirus causing COVID-19 spreads across the globe, with cases surpassing 284,000 worldwide today (March 20), misinformation is spreading almost as fast.
One
persistent myth is that this virus, called SARS-CoV-2, was made by
scientists and escaped from a lab in Wuhan, China, where the outbreak
began.
A new analysis of SARS-CoV-2 may finally put that
latter idea to bed. A group of researchers compared the genome of this
novel coronavirus with the seven other coronaviruses
known to infect humans: SARS, MERS and SARS-CoV-2, which can cause
severe disease; along with HKU1, NL63, OC43 and 229E, which typically
cause just mild symptoms, the researchers wrote March 17 in the journal Nature Medicine.
(Image: © Andriy Onufriyenko/Getty Images)
"Our
analyses clearly show that SARS-CoV-2 is not a laboratory construct or a
purposefully manipulated virus," they write in the journal article.
Kristian
Andersen, an associate professor of immunology and microbiology at
Scripps Research, and his colleagues looked at the genetic template for
the spike proteins that protrude from the surface of the virus. The coronavirus uses these spikes
to grab the outer walls of its host's cells and then enter those cells.
They specifically looked at the gene sequences responsible for two key
features of these spike proteins: the grabber, called the
receptor-binding domain, that hooks onto host cells; and the so-called
cleavage site that allows the virus to open and enter those cells.
That analysis showed that the "hook" part of the spike had evolved to target a receptor on the outside of human cells called ACE2,
which is involved in blood pressure regulation. It is so effective at
attaching to human cells that the researchers said the spike proteins
were the result of natural selection and not genetic engineering.
Here's
why: SARS-CoV-2 is very closely related to the virus that causes severe
acute respiratory syndrome (SARS), which fanned across the globe nearly
20 years ago. Scientists have studied how SARS-CoV differs from
SARS-CoV-2 — with several key letter changes in the genetic code. Yet in
computer simulations, the mutations in SARS-CoV-2 don't seem to work
very well at helping the virus bind to human cells. If scientists had
deliberately engineered this virus, they wouldn't have chosen mutations
that computer models suggest won't work. But it turns out, nature is
smarter than scientists, and the novel coronavirus found a way to mutate
that was better — and completely different— from anything scientists
could have created, the study found.
Another
nail in the "escaped from evil lab" theory? The overall molecular
structure of this virus is distinct from the known coronaviruses and
instead most closely resembles viruses found in bats and pangolins that had been little studied and never known to cause humans any harm.
"If
someone were seeking to engineer a new coronavirus as a pathogen, they
would have constructed it from the backbone of a virus known to cause
illness," according to a statement from Scripps.
Where
did the virus come from? The research group came up with two possible
scenarios for the origin of SARS-CoV-2 in humans. One scenario follows
the origin stories for a few other recent coronaviruses that have
wreaked havoc in human populations. In that scenario, we contracted the
virus directly from an animal — civets in the case of SARS and camels in
the case of Middle East respiratory syndrome (MERS). In the case of
SARS-CoV-2, the researchers suggest that animal was a bat, which
transmitted the virus to another intermediate animal (possibly a
pangolin, some scientists have said) that brought the virus to humans.
In
that possible scenario, the genetic features that make the new
coronavirus so effective at infecting human cells (its pathogenic
powers) would have been in place before hopping to humans.
In
the other scenario, those pathogenic features would have evolved only
after the virus jumped from its animal host to humans. Some
coronaviruses that originated in pangolins have a "hook structure" (that
receptor binding domain) similar to that of SARS-CoV-2. In that way, a
pangolin either directly or indirectly passed its virus onto a human
host. Then, once inside a human host, the virus could have evolved to
have its other stealth feature — the cleavage site that lets it easily
break into human cells. Once it developed that capacity, the researchers
said, the coronavirus would be even more capable of spreading between
people.
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All
of this technical detail could help scientists forecast the future of
this pandemic. If the virus did enter human cells in a pathogenic form,
that raises the probability of future outbreaks. The virus could still
be circulating in the animal population and might again jump to humans,
ready to cause an outbreak. But the chances of such future outbreaks are
lower if the virus must first enter the human population and then
evolve the pathogenic properties, the researchers said.
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