Scientists have found three viruses in bats in Laos that are more similar to SARS-CoV-2 than any known viruses. Researchers say that parts of their genetic code bolster claims that the virus behind COVID-19 has a natural origin — but their discovery also raises fears that there are numerous coronaviruses with the potential to infect people.

David Robertson, a virologist at the University of Glasgow, UK, calls the find “fascinating, and quite terrifying”.

The results, which are not peer reviewed, have been posted on the preprint server Research Square1. Particularly concerning is that 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.

To make the discovery, Marc Eloit, a virologist at the Pasteur Institute in Paris and his colleagues in France and Laos, took saliva, faeces and urine samples from 645 bats in caves in northern Laos. In three horseshoe (Rhinolophus) bat species, they found viruses that are each more than 95% identical to SARS-CoV-2, which they named BANAL-52, BANAL-103 and BANAL-236.