Scientists have discovered another clue to the origins of the virus that causes Covid-19, with bats living in caves in Laos found to be carrying a similar pathogen that experts suggest could potentially infect humans directly.
Researchers from the Pasteur Institute in France and the University of Laos captured 645 bats from limestone caves in northern Laos and screened them for viruses related to SARS-CoV-2. What they found gives credence to the reports that the virus behind COVID-19 has a natural origin.
According to their study, posted to the preprint server Research Square on Sept. 17, among the hundreds of bats tested in Vientiane Province, three were found to carry viruses that closely resemble the virus that causes Covid-19, particularly in the mechanism for latching on to human cells.
In three horseshoe (Rhinolophus) bat species, they found viruses that are each more than 95 percent identical to SARS-CoV-2, which they named BANAL-52, BANAL-103, and BANAL-236.
The new viruses contain receptor binding domains that are almost identical to that of SARS-CoV-2, and can therefore infect human cells. The receptor-binding domain allows SARS-CoV-2 to attach to a receptor called ACE2 on the surface of human cells to enter them.
“The idea was to try to identify the origin of this pandemic,” Marc Eloit, who leads the Pasteur Institute’s pathogen discovery laboratory, told AFP. Eloit, whose team analyzed the samples collected, said there were still key differences between the viruses found and SARS-CoV-2.
Case for natural origin
“When SARS-CoV-2 was first sequenced, the receptor-binding domain didn’t really look like anything we’d seen before,” says Edward Holmes, a virologist at the University of Sydney in Australia. This caused some people to speculate that the virus had been created in a laboratory. But the Laos coronaviruses confirm these parts of SARS-CoV-2 exist in nature, he says.
“I am more convinced than ever that SARS-CoV-2 has a natural origin,” agrees Linfa Wang, a virologist at Duke–NUS Medical School in Singapore.
Alice Latinne, an evolutionary biologist at the Wildlife Conservation Society Vietnam in Hanoi, says that added to recent studies of relatives of SARS-CoV-2 discovered in Thailand, Cambodia, and Yunnan in southern China, this latest study demonstrates that southeast Asia is a “hotspot of diversity for SARS-CoV-2 related viruses.”
It seems that the more scientists learn about the many close relatives of the SARS-CoV-2 virus, the more intriguing and dangerous the viruses become. Last year, researchers described another close relative of SARS-CoV-2, called RaTG13, which was found in bats in Yunnan. It is 96.1 percent identical to SARS-CoV-2 overall and the two viruses probably shared a common ancestor 40–70 years ago.
BANAL-52 is 96.8 percent identical to SARS-CoV-2, says Eloit — and all three newly discovered viruses have individual sections that are more similar to sections of SARS CoV-2 than seen in any other viruses.
Viruses swap chunks of RNA with one another through a process called recombination, and one section in BANAL-103 and BANAL-52 could have shared an ancestor with sections of SARS-CoV-2 less than a decade ago, says Spyros Lytras, an evolutionary virologist at the University of Glasgow. “These viruses recombine so much that different bits of the genome have different evolutionary histories,” he says.
The authors say their findings support the hypothesis that SARS-CoV-2 resulted from the recombination of viral sequences existing in horseshoe bats. The findings are currently being considered for publication in a Nature journal, Bloomberg reported.