Scientists study bats that harbor a near relative to COVID-19 virus

Bats dwelling in limestone caves in northern Laos were found to carry coronaviruses that share a key feature with SARS-CoV-2, moving scientists closer to pinpointing the cause of COVID-19.

Researchers at France’s Pasteur Institute and the University of Laos looked for viruses similar to the one that causes COVID-19 among hundreds of horseshoe bats. They found three with closely matched receptor binding domains — the part of the coronavirus’s spike protein used to bind to human ACE-2, the enzyme it targets to cause an infection.

The finding, reported in a paper released earlier this fall that’s under consideration for publication by a Nature journal, shows that viruses closely related to SARS-CoV-2 exist in nature, including in several Rhinolophus, or horseshoe bat, species. The research supports the hypothesis that the pandemic began from a spillover of a bat-borne virus. About 1,000 such infections may be occurring daily in southern China and Southeast Asia in areas with dense populations of bats from the Rhinolophus genus, a study found.

The three viruses found in Laos, dubbed 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 SARS-CoV-2’s origin and may intrinsically pose a future risk of direct transmission to humans.”

The receptor binding domains of three Laos coronaviruses are closer to that of SARS-CoV-2 than to the RaTG13 virus identified in Rhinopholus affinis bats from the Mojiang mineshaft in Yunnan province, that was regarded as the pandemic strain’s closest match. The BANAL-236 virus has an almost identical receptor binding domain to the pandemic virus, according to the paper.

“The receptor binding domain of SARS-CoV-2 looked 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 wasn’t involved in the research.

“Now that we are sampling more from nature, we are starting to find these closely related bits of gene sequence,” Holmes said in an email. “Eventually, with more sampling, the natural ancestry of the entire SARS-CoV-2 genome will be revealed.”

None of the bat viruses isolated in Laos harbors a so-called furin cleavage site in the spike that facilitates cell entry. It’s a feature of the SARS-CoV-2 virus that has led some scientists to theorize that it was created in a laboratory.

No evidence supporting the lab-leak theory has emerged. In August, the U.S. 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.