MOSCOW, July 28. /TASS/. Molecular biologists from China, the US and Europe compared the genomes of several closest relatives of the SARS-CoV-2 coronavirus and discovered that its ancestors separated from the common evolutionary tree of bat viruses a rather long time ago, about 40 to 70 years. The findings of the team were published in the Nature Microbiology journal.
"It is clear from our analysis that viruses closely related to SARS-CoV-2 have been circulating in horseshoe bats for many decades. The unsampled diversity descended from the […] common ancestor forms a clade of bat sarbecoviruses with generalist properties - with respect to their ability to infect a range of mammalian cells - that facilitated its jump to humans and may do so again," the researchers write.
The scientists seek to understand, when and where the novel coronavirus, which cause the global COVID-19 pandemic, initially appeared, as well as when it started transmitting to humans. There is no consensus among the epidemiologists in this regard so far.
In particular, the biologists cannot say precisely, when and where this virus appeared, what animals - besides bats and pangolins - acted as intermediate carriers, and what role did gene recombination play in its emergence.
A group of molecular biologists led by prof. David Robertson of Edinburgh University (the UK), revealed the evolutionary history of the SARS-CoV-2 ancestors by studying the genomes of six dozens of its closest coronavirus relatives.
Coronavirus evolution history
To do that, the scientists have developed special algorithms that allowed them to remove all traces of recombination from the viral genomes. This is highly important, because exchange of RNA fragments between viruses prevent the scientists from revealing family ties between them and determining the time of their emergence and the speed of their evolution.
After processing the genomes of all studied viruses this way, the scientists created an evolutionary tree for SARS-CoV-2 closest relatives and tried to understand, when this virus separated from its presumed ancestor, the RaTG13, which infects horseshoe bats that live in southern and southeastern China.
These calculations confirmed that the SARS-CoV-2 and the RaTG13 are indeed related to each other, but also revealed that their ancestors separated an unexpectedly long time ago, between 1948 and 1969, depending on the genome analysis method and the viral RNA fragments set. The COVID-19 pathogen and the SARS atypical pneumonia pathogen separated later, between 1952 and 1970.
All this indicates that viruses, similar to SARS-CoV-2, circulate among bats of Southern China for more than half a decade. Considering the special structure of their envelopes that allows them to connect to receptors on the surface of lung cells of a several different species, it explains why not one, but two similar viruses infiltrated the human population and caused serious outbreaks of respiratory infections.
The scientists hope that they would be able to study new coronavirus specimen, harvested from bats living in the Yunnan and Hubei provinces. Analysis and comparison of their genomes with the SARS-CoV-2 would make it possible to specify the time of emergence of the COVID-19 pathogen’s ancestors, and to evaluate, how probable appearance of new such pathogens is.