Are there bats carrying coronaviruses that are direct precursors of SARS-CoV-2? Is it possible to go back to the animal virus that contributed to the emergence of the agent responsible for Covid-19? An article, published on September 17 on Research Square, the pre-publication site for the journals of the Nature group, even if it has yet to pass through the filter of peer review, provides important elements in this regard.
Since the emergence of this new human virus, many animal species have been studied in order to identify possible natural reservoirs and / or intermediate hosts. Studies have shown that SARS-CoV-2 shares a genetic proximity with coronaviruses hosted in insectivorous bats, those of the group of Rhinolophus.
Researchers at the Institut Pasteur in Laos are interested in Rhinolophus living in karstic reliefs sheltering caves serving as breeding sites for these species. The analysis of rectal samples from bats captured between July 2020 and January 2021 then enabled the team led by Marc Eloit from the Institut Pasteur in Paris to identify coronaviruses genetically very close to SARS-CoV-2.
“A future risk of transmission to humans”
All these flying mammals infected with these coronaviruses came from Feuang district in Vientiane province. These viruses were named “BANAL-103”, “BANAL-236”, “BANAL-52” (contraction of “Bat”, “Bat”, and “Anal”). The BANAL-52 genome has a 96.85% identity with SARS-CoV-2. Until now, the coronavirus closest to this has been a strain dubbed “RaTG13”, the complete genetic sequence of which shows 96.2% identity with SARS-CoV-2. RaTG13 was isolated in 2013 in the Mojiang copper mine, in Yunnan province, southwest China, by researchers from the Wuhan Institute of Virology (WIV), the city where the Covid pandemic -19 declared at the end of 2019.
The SARS-CoV-2 envelope contains a protein called “Spike” (“Spicule”). Protein attachment spike to the ACE2 receptor present on the surface of target cells, in particular respiratory cells, constitutes the first step in the infectious process. The protein subregion spike coming into contact with the ACE2 receiver is referred to as “RBD” (Receptor Binding Domain, for “receptor binding domain”). Biologists have shown that bats Rhinolophus from this region of Laos harbor coronaviruses possessing an RBD capable of binding to the ACE2 receptor with high affinity. Their RBD differs by only one or two amino acids (the building blocks of proteins) from that of SARS-CoV-2. By comparison, of the 17 amino acids of the RBD of the coronavirus RaTG613 coming in close contact with the ACE2 receptor, only 11 are identical to those of the RBD of SARS-CoV-2.
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