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Researchers at the Pasteur Institute in France and the University of Laos searched hundreds of horseshoe bats for viruses similar to the one that causes Covid. They found three with very similar receptor-binding domains, the part of the coronavirus spike protein that binds to human ACE-2 (the enzyme that attacks to cause infection).
The conclusion, published in a recent article in the journal Nature, reveals that viruses closely related to SARS-CoV-2 exist in nature, among various species of hornbills. The study confirms the hypothesis that the pandemic began with the spread of the virus transmitted by bats.
The study estimates that around 1,000 similar infections can occur daily in southern China and Southeast Asia, areas where large numbers of Rhinolophus bats breed.
The three viruses found in Laos, called BANAL-52, BANAL-103 and BANAL-236, are “the closest ancestors of SARS-CoV-2 that we know of,” said Marc Eloit, head of pathogen research at the Pasteur Institute of Paris. .
“These viruses may have contributed to the origin of SARS-CoV-2 and, in principle, may represent a risk of direct transmission to humans in the future,” he said.
The receptor-binding domains of the three Lao coronavirus receptors are closer to SARS-CoV-2 than to the RaTG13 virus detected in bats Rhinopholus affinis from the Manggyang mines in Yunnan province, which was considered the closest equivalent. of a pandemic strain. According to the study, the BANAL-236 virus has a receptor-binding domain almost identical to the virus that caused the pandemic.
“The receptor-binding domain of SARS-CoV-2 initially seemed unusual because there were so few viruses that it could be compared to,” said Edward Holmes, an evolutionary biologist at the University of Sydney, who was not involved in the study.
Ancestor tracing
“Now that we are taking more samples from nature, we are beginning to discover closely related fragments of the gene sequence,” he said. E. Holmes wrote in the letter. “Further sampling will reveal the natural ancestors of the entire SARS-CoV-2 genome.”
None of the bat viruses isolated from Laos have a furin cleavage site on the spike that facilitates entry into cells. This is a feature of the SARS-CoV-2 virus that led some scientists to put forward the theory that it was developed in the laboratory.
So far, no evidence has been found to support the theory of laboratory leaks. Last month, US intelligence ruled out the possibility that SARS-CoV-2 was developed in China as a biological weapon, but no consensus was reached on its origins.
According to the study authors, the lack of a furin cleavage site may be explained by insufficient samples from bats, or its appearance in the transmission chains in another vector animal, or circulation in humans in the early stages of an outbreak when the virus caused few symptoms.
“Our results suggest that there are more bat sarbecoviruses that appear to have the same potential to infect humans as the early SARS-CoV-2 strains,” the authors write.
Guano voters
People who spend a lot of time in or near caves, such as guano collectors, are at particular risk of contracting the virus. More studies are needed to assess whether people who have been in contact with bats have been infected with one of these viruses and whether they have antibodies that can protect against future SARS-CoV-2 infections.
“This study is really interesting and we need more like it,” he said. wrote in a letter to Maria Van Kerkhove, technical director of the World Health Organization COVID-19.
The researchers studied 645 bats representing 46 species captured in four areas, Fueng and Meth in Vientiane and Namor and Xay in Oudomxay, as of 2020. July to 2021 January.
Bats live in the limestone karst area of the Indochinese peninsula, typical of China, Laos, and Vietnam.
The article highlights the diversity of SARS-CoV-2-like viruses found in bats in Southeast Asia, Holmes says.
“Continuous sampling is the only way to understand the origin of this virus, so it is important that as many samples are taken as possible throughout China, as it remains the most likely place of origin,” he says. – The study emphasizes that bat coronaviruses, which can infect humans, exist in nature and can occur at any time. That is a clear risk for the future. “
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