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Newly Discovered Bat Viruses Give Hints to Covid’s Origins - The New York Times
Oct 14, 2021 3 mins, 30 secs

Coronaviruses discovered in Laotian bats are surprisingly adept at infecting human cells, showing that such deadly features can indeed evolve outside of a lab.

Three of the Laos coronaviruses were unusual: They carried a molecular hook on their surface that was very similar to the hook on the virus that causes Covid-19, called SARS-CoV-2.

Like SARS-CoV-2, their hook allowed them to latch onto human cells.

“It is even better than early strains of SARS-CoV-2,” said Marc Eloit, a virologist at the Pasteur Institute in Paris who led the study, referring to how well the hook on the Laos coronaviruses binds to human cells.

Some people have speculated that SARS-CoV-2’s impressive ability to infect human cells could not have evolved through a natural spillover from an animal.

Three bats captured in northern Laos carried viruses that were remarkably similar to SARS-CoV-2, the virus that causes Covid-19.

Three bat viruses genetically more similar to SARS-CoV-2 than RaTG13, which was previously thought to be the closest relative.

Three bat viruses genetically more similar to SARS-CoV-2 than RaTG13, which was previously thought to be the closest relative.

Three bat viruses genetically more similar to SARS-CoV-2 than RaTG13, which was previously thought to be the closest relative.

RaTG13, as it is known, shares 96 percent of its genome with SARS-CoV-2

Based on the mutations carried by each virus, scientists have estimated that RaTG13 and SARS-CoV-2 share a common ancestor that infected bats about 40 years ago

Both viruses infect cells by using a molecular hook, called the “receptor-binding domain,” to latch on to their surface

RaTG13’s hook, adapted for attaching to bat cells, can only cling weakly to human cells

SARS-CoV-2’s hook, by contrast, can clasp cells in the human airway, the first step toward a potentially lethal case of Covid-19

To find other close relatives of SARS-CoV-2, wildlife virus experts checked their freezers full of old samples from across the world

They identified several similar coronaviruses from southern China, Cambodia, and Thailand

They traveled to northern Laos, about 150 miles from the mine where Chinese researchers had found RaTG13

The bats harbored two dozen kinds of coronaviruses, three of which were strikingly similar to SARS-CoV-2 — especially in the receptor-binding domain

In RaTG13, 11 of the 17 key building blocks of the domain are identical to those of SARS-CoV-2

But in the three viruses from Laos, as many as 16 were identical — the closest match to date

Although the Laotians did not show signs of having been infected with SARS-CoV-2, they carried immune markers, called antibodies, that appeared to be caused by a similar virus

Linfa Wang, a molecular virologist at the Duke-NUS Medical School in Singapore who was not involved in the study, agreed that such an infection was possible, since the newly discovered viruses can attach tightly to a protein on human cells called ACE2

Paradoxically, some other genes in the three Laotian viruses are more distantly related to SARS-CoV-2 than other bat viruses

If a bat infected with one coronaviruses catches a second one, the two different viruses may end up in a single cell at once

As that cell begins to replicate each of those viruses, their genes get shuffled together, producing new virus hybrids

In the Laotian coronaviruses, this gene shuffling has given them a receptor-binding domain that’s very similar to that of SARS-CoV-2

Lytras and his colleagues are now comparing SARS-CoV-2 not just to the new viruses from Laos, but to other close relatives that have been found in recent months

He and his colleagues are now drawing the messy evolutionary trees of SARS-CoV-2-like viruses based on these new insights

Eloit believes the best bet is a zone of Southeast Asia that includes the site where his colleagues found their coronaviruses, as well as the nearby mine in Yunnan where RaTG13 was found

government’s new virus-hunting project, called DEEP VZN, may turn up one or more SARS-CoV-2-like viruses in that region

Worobey of the University of Arizona said that some bat coronaviruses carrying SARS-CoV-2-like segments have been found in eastern China and Thailand

Bats as far east as Indonesia and as far west as India, he noted, share many biological features with the animals known to carry SARS-CoV-2-like viruses

Just seven coronaviruses are known to have jumped the species barrier to become well-established human pathogens

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