The ancestors of the new coronavirus have been able to circulate bats unnoticed for decades. And these coronaviruses probably also had the ability to infect humans, according to a new study.
To understand where the new coronavirus, known as SARS-CoV-2, comes from and how it spreads in humans, scientists need to trace its evolutionary history through the genes of the virus, which are encoded in ribonucleic acid or RNA. But the evolutionary history of SARS-CoV-2 is complicated because coronaviruses it is known that they are often exchanged genetic material with other coronaviruses.
This gene exchange, called genetic recombination, also makes it difficult for scientists to determine how the coronavirus first spread to humans; some researchers suggest direct transmission from a bat to a human, while others hypothesize that there was a medium species, such as pangolinsinvolved.
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In the new study, researchers first identified sections of RNA in the SARS-CoV-2 genome that develop “as a whole piece,”
They then compared these genetic regions with those of similar coronaviruses found in bats and pangolins. Adding evidence to support previous findings, they found that SARS-CoV-2 was most closely associated with another bat coronavirus known as RaTG13.
In previous studies, researchers looked specifically at genes responsible for the so-called receptor-binding domain (RBD) of the coronavirus. “spike” protein – the piece that allows the virus to bind to the ACE2 receptor in human cells and infect them. This study found that the RBD portion of the thorn protein is genetically more similar to the coronavirus found in pangolins (called Pangolin 2019) than that of RaTG13. There are two possible explanations for this finding: first, that the SARS-CoV-2 virus has developed its ability to spread to humans with pangolins (unlikely, given that SARS-CoV-2 is more closely related to RaTG13 of all known pangolin viruses), or second, that SARS-CoV-2 acquired this RBD by recombination with pangolin virus, Bonnie said.
But in the new analysis, the researchers found no evidence of recombination in the genes for the SARS-CoV-2 spike protein. Instead, new genetic sequencing data suggest a third explanation for what happened: The genes for the spiny protein and thus the ability of the coronavirus to infect human cells were passed on from a common ancestor who eventually gave birth to all three coronaviruses: SARS-CoV-2 , RaTG13 and Pangolin-2019.
The authors note that it is still possible that pangolins “or another hitherto undiscovered species” acted as an intermediate host that helped the virus spread to humans. But it’s unlikely, Bonnie said. Rather, the new findings suggest that the ability to replicate in the upper respiratory tract in both humans and pangolins has actually evolved in bats. From bats, SARS-CoV-2 could spread directly to humans.
It has been circulating for decades
But when did the pedigree that gave rise to SARS-CoV-2 first deviate from the other two viral lines? To understand this, the researchers identified mutations or differences in specific nucleotides – the molecules that make up coronavirus RNA – among different viruses. They then counted the number of mutations present in the regions of the SARS-CoV-2 genome that did not undergo recombination. And knowing the approximate rate at which the coronavirus mutates each year, they calculated how much time had elapsed since the divergence of the three.
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They found that more than a century ago, there was a single line that would eventually lead to SARS-CoV-2, RaTG13 and Pangolin-2019 viruses. Even then, “this genus probably had everything it needed amino acids at its receptor-binding site to infect human cells, “said Bonnie. (Amino acids are the building blocks of proteins such as thorn protein).
At that time, the Pangolin-2019 virus differed from the SARS-CoV-2 and RaTG13 viruses. Then, in the 1960s or 1970s, this line split into two, creating the RaTG13 origin and the SARS-CoV-2 line. Sometime between 1980 and 2013, the RaTG13 line lost its ability to bind to human receptors, but SARS-CoV-2 did not.
“The SARS-CoV-2 family line has been circulating in bats for 50 or 60 years before jumping on humans,” Bonnie said. At the end of 2019, “someone just got very unhappy” and got in touch with SARS-CoV-2 and it started pandemic,,
There are probably other viral genera from the same ancestor of the century that have also undergone decades of evolution, “which we simply did not characterize,” Bonnie said. “The question is, ‘Are there half a dozen of these genera, 20 or a hundred?’ “- and no one knows.” But there are probably other people hiding in bats that are able to spread in humans, he said.
“This paper provides more clues to understanding how this and other coronaviruses can occur,” said Dr. Amesh Adala, an infectious disease expert at the Johns Hopkins Health Security Center in Baltimore who was not part of the study. . “We really only know the tip of the iceberg when it comes to the viruses that get into bats.” Seeing that the relatives of the coronavirus have been around for so many years, he suggests that there are so many without samples. “As far as pandemic preparedness is concerned, having a much stronger surveillance system is really the only way we will protect ourselves from these threats in the future,” Adalja said.
Many virus samples are being taken from poultry and wild birds in East Asia, Southeast Asia and other parts of the world to prevent a potential bird flu pandemic, Bonnie said. “If someone gets infected with a bird flu virus, the feedback time to understand that this would be something like 48 hours and we would immediately understand that this person should be isolated immediately and other measures should follow. “But for bat coronaviruses there are no such preventive measures, he added.
More than a month has passed since SARS-CoV-2 first spread to humans so that scientists can have the genome of the new coronavirus – long enough for the virus to spread to a thousand people, Bonnie said. “It was too late at this point.”
The findings were published in the magazine on July 28 Natural microbiology,,
Originally published in Live Science.