The ancestors of the coronavirus novel may have been circulating in bats for decades. And those 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 to humans, scientists need to trace its evolutionary history through the virus’s genes, which are encoded in ribonucleic acid. , or RNA. But the evolutionary history of SARS-CoV-2 is complicated, because coronavirus they are known to exchange frequently genetic material with another coronavirus.
This gene alteration, called genetic recombination, also makes it difficult for scientists to limit how the coronavirus spreads to humans first; some researchers propose direct human-to-human transmission, while others hypothesize that there were middle species, such as pangolini, involved.
Related: Coronavirus News: Live Updates
In the new study, the researchers identified the first sections of RNA in the SARS-CoV-2 genome that were evolving “as a whole,”; without genetic recombination, for how much they could study, said co-lead author Maciej Boni, an associate professor of biology at the Penn State Center for Infectious Disease Dynamics.
They then compared these genetic regions with those of a similar coronavirus found in bats and pangolins. Adding evidence to support previous findings, they discovered that SARS-CoV-2 was most closely related to bat coronavirus, known as RaTG13.
In previous studies, scientists have specifically examined the genes responsible for the so-called coronavirus receptor binding domain (RBD). ” “Pointed” protein – the piece that allows the virus to attach to the ACE2 receptor in human cells and infect them. That research found that the RBD portion of the tip protein was genetically more similar to a 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 evolved in its ability to spread to humans in pangolins (most likely, because SARS-CoV-2 is more closely related to RaTG13 than any known pangolin virus), or second, that SARS-CoV-2 had acquired this RBD through recombination with the pangolin virus, Boni said. .
But in the new analysis, the researchers found no evidence of recombination in the SARS-CoV-2 spike protein genes. Instead, new genetic sequencing data suggests a third explanation for what happened: The genes for the pointed protein, and therefore the ability of the coronavirus to infect human cells, were passed down from a common ancestor. which eventually led to all three coronaviruses: SARS-CoV-2, RaTG13 and Pangolin-2019.
The authors note that it is still possible that pangolins “or other species have not yet been discovered” may have acted as an intermediate host that helped the virus spread to humans. But “it’s unlikely,” Boni said. Rather, the new findings suggest that the ability to replicate in the upper respiratory tract of both humans and pangolins has actually evolved into bats. From bats, SARS-CoV-2 could be spread directly to humans.
Reward for decades
But when did the lineage that led to SARS-CoV-2 first diverge from the other virus lineage? To name a few, the researchers identified mutations or differences in specific nucleotides – the molecules that make up the coronavirus RNA – among the different viruses. They then reported the number of mutations present in the regions of the SARS-CoV-2 genome that had not undergone recombination. And knowing the estimated rate at which the coronavirus dies each year, they calculated how long it had been since the three divergent.
Related: The coronavirus was not engineered in a laboratory. Here’s how we know.
They found that more than a century ago, there was one lineage that eventually led to SARS-CoV-2, RaTG13 and Pangolin-2019 viruses. Even then, “this lineage probably had everything it needed Amino acids at the site that binds to its receptor to infect human cells, “Boni said. (Amino acids are the building blocks.” proteins such as tip protein).
At that time, the Pangolin-2019 virus diverged from the SARS-CoV-2 and RaTG13 viruses. Then, in the 1960s or 1970s, this lineage split in two, creating the RaTG13 lineage and the SARS-CoV-2 lineage. Sometime between 1980 and 2013, the RaTG13 lineage lost its ability to bind to the human receptor, but SARS-CoV-2 did not.
“The SARS-CoV-2 lineage circulated in bats for 50 or 60 years before jumping into humans,” Boni said. Near the end of 2019, “someone was just very unlucky” and got in touch with SARS-CoV-2 and stopped pandemic.
There is probably another lineage of virus from the ancestor of the same century that has also gone through decades of evolution, “which we have just not characterized,” Boni said. “The question is, ‘Are there half a dozen of these lineages, 20, or a hundred?’ – and no one knows. ”But it’s likely there are others out there hiding in bats that are capable of spreading to humans, he said.
“This paper provides more clues to understanding how this and other coronaviruses can come out,” said Dr. Amesh Adalja, an infectious disease expert at the Johns Hopkins Center for Health Security in Baltimore, who was not part of the study. “We really only know the tip of the iceberg when it comes to viruses that are linked to bats.” To see that the relatives of the coronavirus have been around for so many years, suggests that there is so much to sample. “When it comes to pandemic preparedness, having a much stronger surveillance system is the only way we will look at these threats in the future,” Adalja said.
Many virus samples are made in domestic and wild birds in East Asia, Southeast Asia and other parts of the world in an effort to prevent potential pandemics of bird flu, he said. Good. “If someone gets infected with poultry influence virus, the waking time I understand to be something like 48 hours and we would immediately know that this person needs to be isolated immediately and should follow other measures. “But for bat coronavirus, there is no such preventative measure,” he added.
More than a month has passed since SARS-CoV-2 first spread to humans because scientists have the new coronavirus genome in their hands – enough time for the virus to spread to a thousand people, Boni said. “That point was too late.”
The findings were published July 28 in the journal Microbiology of Nature.
Originally published on Live Science.