The Omicron variant of the virus that causes COVID-19 has so many mutations that it could be the result of “ping-pong” transmission between humans and mice or other rodents, according to a new paper released Tuesday.
The pre-print study, which has not yet been peer-reviewed or accepted for publication, was conducted by a large team of international researchers from both private companies and institutions such as the University of Washington and the Italian National Institute of Molecular Genetics.
“The unprecedented number of substitutions found in the Omicron genome raises questions about its origin,” the authors write.
To test the theory of transmission between species, the scientists examined whether Omicron would bind to receptors in mouse, mink or pangolin cells.
They found that Omicron would bind to mouse cells but not the other animals – and said previous variants of the virus did not bind to any of the three. They also found that certain Omicron mutations made it more likely to bind to human cells as well.
“Taken together, these results suggest that mutations in Omicron’s (receptor-binding domains) enabled it to adapt to rodents and contributed to potentially increased transmission in humans,” they said. They described binding to mouse cells and bypassing immunity as a “major SARS-CoV-2 mutation shift”.
The authors emphasized that the interspecies transfer theory is just that, one of many that has so far been put forward for the development of omicrons. (Others have previously speculated that it could have developed in a single immunocompromised person with a long-lasting infection.)