In RaTG13, 11 of the 17 key building blocks of the domain are identical to those of SARS-CoV-2. But in the three viruses from Laos, as many as 16 were identical — the closest match to date.
Dr. Eloit speculated that one or more of the coronaviruses might be able to infect humans and cause mild disease. In a separate study, he and colleagues took blood samples from people in Laos who collect bat guano for a living. Although the Laotians did not show signs of having been infected with SARS-CoV-2, they carried immune markers, called antibodies, that appeared to be caused by a similar virus.
Linfa Wang, a molecular virologist at the Duke-NUS Medical School in Singapore who was not involved in the study, agreed that such an infection was possible, since the newly discovered viruses can attach tightly to a protein on human cells called ACE2.
“If the receptor binding domain is ready to use ACE2, these guys are dangerous,” Dr. Wang said.
Paradoxically, some other genes in the three Laotian viruses are more distantly related to SARS-CoV-2 than other bat viruses. The cause of this genetic patchwork is the complex evolution of coronaviruses.
If a bat infected with one coronaviruses catches a second one, the two different viruses may end up in a single cell at once. As that cell begins to replicate each of those viruses, their genes get shuffled together, producing new virus hybrids.
In the Laotian coronaviruses, this gene shuffling has given them a receptor-binding domain that’s very similar to that of SARS-CoV-2. The original genetic swap took place about a decade ago, according to a preliminary analysis by Spyros Lytras, a graduate student at the University of Glasgow in Scotland.
Mr. Lytras and his colleagues are now comparing SARS-CoV-2 not just to the new viruses from Laos, but to other close relatives that have been found in recent months. They’re finding even more evidence of gene shuffling. This process — known as recombination — may be reshaping the viruses from year to year.