Did Omicron originate in MICE? Researchers say analysis suggests extremely-transmissible variant evolved in rodents before jumping back to humans
- Chinese scientists say Omicron’s DNA suggest it first emerged in mice
- They said it has mutations that made it better able to infect the animal group
- But most scientists say it likely emerged in an immunocompromised patient
Omicron could have jumped into humans from mice, scientists say.
The mysterious origin of the heavily-mutated Covid variant that triggered global panic only a month ago continues to puzzle experts.
But Chinese scientists now say they may have unearthed evidence linking the mutant strain to mice — in its DNA.
Analysis showed the variant carries 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 other mutant strains, which the scientists held up as yet more proof it did not emerge in humans.
This is not the first time experts have raised the prospect that the variant first appeared in rodents before jumping back into humans.
But most scientists agree that Omicron likely emerged after a prolonged infection in an immunocompromised person, such as an HIV patient.
Some scientists argue that Omicron evolved in mice before jumping back into humans (stock picture). Others say, however, that it likely emerged in an immunocompromised patient
In the study, researchers compared the DNA of Omicron to the original Wuhan virus and other variants including Alpha and Delta which sparked last summer’s wave.
They found it had a much higher average 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 animal species’.
They also compared Omicron to mutations in 13 little-known Covid strains that had previously been found to infect mice.
Results showed it shared five mutations with this group, which the scientists claimed was further evidence it had emerged in mice.
The mutations include K417 and E484, which makes it easier for Omicron to escape antibody protection, N501, which is linked with increased infectivity.
Omicron also includes mutations Q493 and Q498, which the researchers said makes it better suited to infect mice.
Professor Jianguo Xu, from China’s National Institute for 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 over time in mice, before it was transmitted back to humans by reverse zoonotic.
‘These findings suggest that researchers should focus on SARS-CoV-2 variants isolated from wild animals, especially rodents.
‘If Omicron is determined to have been derived from mice, the implications of it circulating among non-human hosts will pose new challenges in the prevention and control of the epidemic.’
Some scientists — including Professor Kristian Andersen at the US-based Scripps Research Institute — have suggested that Omicron may have emerged in mice.
They argue this could explain why it carries so many mutations that are radically different from other variants.
But the argument is yet to gain much traction among scientists.
Many still argue it likely emerged either in an immunocompromised patient or in an area where Covid surveillance is very poor.
The study was published in the Journal of Biosafety and Biosecurity.
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