Bats that inhabit limestone caves in northern Laos were found to be carriers of coronavirus that share a key characteristic with SARS-CoV-2, which brought scientists closer to identifying the cause of COVID-19.
Researchers from the Pasteur Institute in France and the University of Laos looked for viruses similar to the one that causes COVID among hundreds of horseshoe bats. They found three with very similar receptor-binding domains: the part of the coronavirus spike protein that is used to bind to human ACE-2, the enzyme it targets to cause infection.
The finding, reported in an article published Friday that is being considered for publication by a journal Nature, shows that viruses closely related to SARS-CoV-2 exist in nature, including in several species of Rhinolophus or horseshoe bats. . The research supports the hypothesis that the pandemic started from the spread of a virus transmitted by bats.. About 1,000 of these infections may be occurring daily in southern China and Southeast Asia in areas with dense populations of Rhinolophus bats, a study found Tuesday.
The three viruses found in Laos, called BANAL-52, BANAL-103 and BANAL-236, are “the closest ancestors of SARS-CoV-2 known to date,” said Marc Eloit, head of pathogen discovery at the Pasteur Institute in Paris and co-authors. “These viruses may have contributed to the origin of SARS-CoV-2 and may inherently present a future risk of direct transmission to humans.”
The receptor-binding domains of three Lao coronaviruses are closer to those of SARS-CoV-2 than to the RaTG13 virus identified in Rhinopholus affinis bats from the Mojiang mine shaft in Yunnan province, which was considered to be the strain closest to pandemic. The BANAL-236 virus has a receptor-binding domain almost identical to that of the pandemic virus, according to the article.
“The SARS-CoV-2 receptor-binding domain seemed unusual when it was first discovered because there were so few viruses to compare it to,” said Edward Holmes, an evolutionary biologist at the University of Sydney, who was not involved in the research. .
Tracing ancestors
“Now that we are taking more samples from nature, we are beginning to find these closely related fragments of genetic sequence,” Holmes said in an email Saturday. “Eventually, with more samples, the natural ancestry of the entire SARS-CoV-2 genome will be revealed.”
None of the bat viruses isolated in Laos harbor a furin cleavage site on the spike that facilitates cell entry. It is a feature of the SARS-CoV-2 virus that has led some scientists to theorize that it was created in a laboratory.
No evidence has emerged to support the theory of laboratory leaks. Last month, the US intelligence community ruled out the possibility that SARS-CoV-2 was developed by China as a biological weapon, but no consensus was reached on its origin.
The lack of furin cleavage may be explained by insufficient sampling in bats, or by the acquisition of the furin cleavage site during transmission chains in an alternative animal host, or during unreported circulation in humans in the early stages. of the outbreak when the virus may have caused few symptoms, the authors said.
“Our results point to the presence of new bat sarbecoviruses that appear to have the same potential to infect humans as the early SARS-CoV-2 strains,” they said.
Guano collectors
People who spend time in or near caves, such as guano collectors, are at special risk of exposure. More research is needed to assess whether people exposed to bats have been infected with one of these viruses and whether they have antibodies that can provide protection against subsequent SARS-CoV-2 infections.
“This document is really interesting and we need more research like this one,” Maria Van Kerkhove, World Health Organization technical lead for COVID-19, said in an email.
The researchers studied 645 bats of 46 species captured at four sites, in the Fueng and Meth districts of Vientiane province, and in the Namor and Xay districts of Oudomxay province, between July 2020 and January 2021. The Bats live in the limestone karst terrain common in China, Laos, and Vietnam on the Indochina peninsula.
The document highlights the diversity of viruses similar to SARS-CoV-2 present in bats in Southeast Asiasaid Holmes.
“Continuous sampling is the only way to understand the origins of this virus and it is important that more sampling is done throughout China as this remains the most likely place of origin,” he said. “This study emphasizes that bat coronaviruses that have the potential to infect humans readily exist in nature and could emerge at any time. This is the clear risk for the future. “
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