Did Omicron originate in MICE?

Omicron might have jumped from mice into humans, scientists say.

The mysterious origins of the highly mutated Covid strain that sparked global panic just a month ago continues to confuse experts.

But Chinese scientists now say they may have found evidence linking the mutant strain to mice — in its DNA.

Analysis showed the variant contains mutations that make it better at infecting the animal group – which previous research has shown can catch Covid from humans.

And that it has many more mutations than any of the other mutant strains, which the scientists argued is even more proof that it didn’t originate in humans.

This isn’t the first time experts have suggested the prospect of the variant first appearing in rodents before leaping back into humans.

But most scientists agree that Omicron probably arose after a long-term infection in an immunocompromised person, such as an HIV patient.

In the study, researchers compared Omicron’s DNA to the original Wuhan virus and other variants, including Alpha and Delta, that sparked last summer’s wave.

They found that it had a much higher mean number of mutations (53.3) than other mutant strains (28.4 to 35.4).

And that its closest relative was the Gamma variant – which emerged in Brazil – although the two split into separate groups in mid-2020.

This “long branch,” the scientists said, suggested it “may have evolved in a non-human species.”

They also compared Omicron to mutations in 13 little-known Covid strains previously found to infect mice.

The results showed it shared five mutations with this group, which the scientists said was further evidence that it originated in mice.

Professor Jianguo Xu, of China’s National Institute of Communicable Diseases, said Omicron’s mutation profile “shows that the virus has adapted to infect the cells of mice.”

He added: ‘We believe that Covid slowly accumulated mutations in mice over time, before being transferred to humans by reverse zoonosis.

These findings suggest that researchers should focus on SARS-CoV-2 variants isolated from wild animals, especially rodents.

“If Omicron is determined to be mouse-derived, the implications of circulating it among non-human hosts will pose new challenges in the prevention and control of the epidemic.”

Some scientists — including Professor Kristian Andersen of the US-based Scripps Research Institute — have suggested that Omicron may have originated in mice.

They argue that this could explain why it contains so many mutations that are radically different from other variants.

But the argument has yet to gain a lot of traction among scientists.

Many still argue that it probably originated in an immunocompromised patient or in an area where Covid surveillance is very poor.

The research is published in the Journal of Biosafety and Biosecurity.