Omicron variant may have evolved in rats, one theory says - Livescience.com

There are several theories as to how the omicron variant evolved.

The newly identified omicron coronavirus variant may have evolved in a nonhuman animal species, potentially a rodent, some scientists suggest.

Compared with other theories about omicron's origin, such as it evolving in an immunocompromised person or in a human population with poor viral surveillance, "this reverse zoonosis followed by new zoonosis seems more likely to me, given just the available evidence of the really deep branch," meaning the early split from other coronavirus variants, "and then the mutations themselves, because some of them are quite unusual," Andersen said.

Omicron carries seven mutations that would allow the variant to infect rodents, such as mice and rats; other variants of concern, like alpha, carry only some of these seven mutations, Robert Garry, a professor of microbiology and immunology at Tulane Medical School, told STAT.

In addition to these "rodent adaptation" gene variants, omicron carries a slew of mutations not seen in any other versions of SARS-CoV-2, and some scientists take this as potential evidence that the variant emerged in an animal host, Science reported.

Evidence suggests that the alpha variant may have acquired mutations in this way, but this has yet to be confirmed for omicron, Science reported. .

If it didn't emerge in either an animal or immunocompromised person, Omicron may have first appeared in a population with poor viral surveillance, meaning it may have spread and evolved, unnoticed, for upwards of a year.

"I assume this evolved not in South Africa, where a lot of sequencing is going on, but somewhere else in southern Africa during the winter wave," Christian Drosten, a virologist at Charité University Hospital Berlin, told Science.

Nicoletta Lanese is a staff writer for Live Science covering health and medicine, along with an assortment of biology, animal, environment and climate stories.