On November 24, 2021, scientists in South Africa revealed that they had discovered a worrying new variant of SARS-CoV-2.<\/p>\n
They reported that the variant was spreading very rapidly in southern Africa and contained a large number of unusual mutations likely to make the virus more infectious than previous variants.<\/p>\n
Within days of the scientists announcement, the World Health Organization (WHO) declared that the new variant, called Omicron, was a variant of concern.<\/p>\n
Confirming the scientists early fears, by early January 2022, Omicron was driving an unprecedented surge in cases worldwide.<\/p>\n
Many of the mutations that health experts identified in Omicron are rare among previously sequenced variants of the virus.<\/p>\n
This presents a puzzle for scientists because there are no known intermediate variants to reveal how Omicron evolved. It is almost as if the new variant appeared out of nowhere.<\/p>\n
There are three alternative theories for the origin of Omicron:<\/p>\n
The second theory is the most popular among virologists and epidemiologists.<\/p>\n
However, some experts have argued that other viruses, such as the influenza virus, tend to become less infectious over time in individuals with compromised immune systems. <\/p>\n
They cite evidence that while such viruses evolve adaptations to their hosts immune system, they accumulate other mutations that make them less able to cause infections in other people.<\/p>\n
However, Omicron appears to be more infectious than all previously known variants.<\/p>\n
Researchers at the Chinese Academy of Sciences in Beijing have now found evidence that Omicron may have evolved its large collection of unusual mutations in mice.<\/p>\n
They believe that an earlier variant, from the lineage known as B.1.1, jumped from a human into a mouse in mid-2020. Over time, it evolved a range of adaptations to its new host before causing an infection in another human in late 2021.<\/p>\n
They identified 45 point mutations in the RNA of Omicron that they propose occurred after the variant split from its last known common ancestor in humans.<\/p>\n
Point mutations are substitutions of single chemical letters, known as bases, in the four-letter genetic code.<\/p>\n
Past research suggests RNA viruses tend to pick up more mutations in particular bases, according to which animal host they are replicating inside.<\/p>\n
Using this knowledge, the authors of the new paper have previously identified the mutation signature of different animal hosts of SARS-CoV-2.<\/p>\n
Their new study found that the relative frequency of the new point mutations in Omicron is characteristic of evolution in a mouse host rather than a human host.<\/p>\n
They discovered that the mutation signature of Omicron is different from several variants known to have evolved in humans, including three variants isolated from patients with chronic COVID-19.<\/p>\n
The scientists also found that several mutations in Omicrons spike protein, which SARS-CoV-2 uses to cause infection in host cells, help the virus bind more tightly to its target receptor in mice. <\/p>\n
They have published their findings in the Journal of Genetics and Genomics.<\/p>\n
In the paper, they conclude:<\/p>\n
Collectively, our results suggest that the progenitor of Omicron jumped from humans to mice, rapidly accumulated mutations conducive to infecting that host, then jumped back into humans, indicating an inter-species evolutionary trajectory for the Omicron outbreak.<\/p>\n
Biologist Matt Ridley, author of Viral: The Search for the Origin of COVID-19, responded to the study on Twitter:<\/p>\n
Looks like Omicron developed from a human variant in a mouse. The question is: what mice and where? House mice in homes? Or lab mice in labs?<\/p>\n
We believe that Omicron likely evolved in a wild mouse population, the senior author of the study, Wenfeng Qian, Ph.D., told Medical News Today. <\/p>\n
He said that mutations in the spike protein of Omicron significantly overlapped with mutations in SARS-CoV-2 viruses that have adapted to a mouse host.<\/p>\n
However, 18 out of a total of 25 mutations in the Omicron spike were not present in any of the SARS-CoV-2 viruses they studied that were adapted to lab mice. <\/p>\n
In addition, he pointed out that Omicron appears to have diverged from the B.1.1 lineage, with which it shares seven mutations. <\/p>\n
It is implausible that a lab will use a B.1.1 variant for their mouse adaptation experiments, he commented. Instead, he said they would most likely use a strain of SARS-CoV-2 that researchers sequenced at the start of the pandemic, known as Wuhan-Hu-1.<\/p>\n
Evolutionary biologist Mike Worobey, Ph.D., of the University of Arizona in Tucson, said the most plausible theory remained that Omicron evolved in an immune-compromised patient with a protracted [SARS-CoV-2] infection.<\/p>\n
I think their approach is really interesting, but I still think it is more likely that the unusual array of mutations in Omicron occurred in a chronically human [with the infection], he told MNT.<\/p>\n
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\nCOVID-19: Did Omicron evolve in mice? - Medical News Today<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"