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Did Omicron originate in mice before jumping to humans?

  • 25 Jan 2022

Chinese scientists say Omicron’s DNA suggests it first emerged in rodents. However, most scientists remain skeptical of an animal origin theory.

( AP )

The Omicron variant may have originated in mice before jumping to humans, according to some scientists.

Since the heavily mutated Covid-19 variant sparked global panic a month ago and spread rapidly to emerge as the dominant strain in many countries, experts have been puzzled by its origin.

A new study published in the Journal of Biosafety and Biosecurity appears to support the animal transmission theory, with Chinese scientists claiming there is evidence that links Omicron’s DNA to mice.

“Our study calculated the average number of mutations in the five VOCs and investigated the key mutations in the viral S protein, where the infection originates. We found that the Omicron variant contains mutations at five key sites of the protein: K417, E484, Q493, Q498, and N501,” said Professor Jianguo Xu from the National Institute for Communicable Diseases Control and Prevention China, who led the research.

K417 and E484 make it easier for Omicron to escape antibody protection, while N501 is linked to increased infectivity. Mutations Q493 and Q498 indicate that it is better suited to infect mice.

After comparing Omicron to mutations in 13 little-known Covid strains that had previously been found to infect mice, Xu argued the most likely intermediate host to be a rodent.

“This mutation profile shows that the virus has adapted to infect the cells of mice. In addition, the time-scaled phylogenetic tree shows that the Omicron and Gamma lineages were likely circulating in mid-2020, which supports the hypothesis that Omicron may have evolved in a non-human animal species.”

“We believe that the coronavirus slowly accumulated mutations over time in mice, before it was transmitted back to humans by reverse zoonotic.”

The Omicron variant was first reported in South Africa on November 24, 2021. The strain is distinct in that it contains 45 mutations, some of which appear to make it resistant to vaccines and more infectious compared to other variants.

Some other scientists like Professor Kristian Andersen, an immunologist at the Scripps Research Institute in California, have also suggested that Omicron may have emerged in mice.

However, there are some drawbacks to this theory.

For one, SARS-CoV-2 isn’t great at infecting mice – the part of mouse cells that the virus would typically use to gain entry has little affinity for the standard SARS-CoV-2 spike protein.

Other researchers have managed to adapt SARS-CoV-2 to infect mice in the lab, raising the question of whether lab animals are involved in its origins, as it’s not been documented in the real world.

This makes it difficult, albeit not impossible, to understand how the virus made this leap from humans into mice.

Scientists in general have been skeptical of the animal origin story of Omicron, although most believe it’s too early to understand the origins of the variant.

The prevailing consensus is that it likely emerged either in an immunocompromised patient or in an area where Covid-19 surveillance is very poor.

Nevertheless, it’s an important question to help predict and prevent the rise of dangerous variants in the future.

“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,” Professor Xu said.

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