The Origin of the Omicron Variant: A Hypothesis of Animal Cross-Species Evolution

The Omicron variant has already spread around the world, causing huge numbers of infections in many countries, including unprecedented records in the US, UK, Australia and many places in Europe . Although it appears milder than previous variants of the coronavirus, its high transmissibility — as well as its ability to partly evade antibodies acquired after previous infection or vaccination — could still lead to high rates of hospitalization and death.

One of the most puzzling aspects of this variant is the high number of mutations it has acquired compared to previous strains, such as the wild-type virus first discovered in Wuhan in 2019. Given that Omicron is clearly not a direct descendant of other variants of concern such as Whether it is Alpha, Beta or Delta, scientists want to know where this variant originated and how it managed to acquire such extraordinary contagiousness.

One hypothesis regarding the origin of Omicron is that it began circulating in mid-2020 in a location without much surveillance or genetic testing capacity (perhaps an African country), and that A year and a half later, he managed to detect so many mutations that he practically “exploded onto the scene” in November, in the South African province of Gauteng. However, this theory is unlikely given that such a contagious coronavirus strain would likely have been detected much earlier.

Another hypothesis is that one of the previous SARS-CoV-2 variants (or perhaps even the Wuhan wild type) may have infected a severely immunocompromised person (perhaps an untreated HIV patient). The virus was not fatal, but remained in the individual’s body long enough to acquire a large number of mutations. The most troubling question with this theory, however, is how the variant was not spread by this person sooner.

A new study published in the Journal of Genetics and Genomics offers a fascinating alternative hypothesis. According to a research team led by the Chinese Academy of Sciences, the rapid accumulation of mutations in the Omicron variant that enabled its runaway global outbreak suggests its proximal origin could be an animal rather than a human host – most likely from mouse.

“The molecular spectrum of mutations acquired by Omicron’s ancestor was significantly different from the spectrum of viruses that evolved in human patients, but resembled the spectrum associated with virus evolution in a mouse cellular environment,” the researchers wrote. authors of the study.

“Additionally, Omicron spike protein mutations significantly overlapped with SARS-CoV-2 mutations known to promote adaptation to mouse hosts, particularly through enhanced spike protein binding affinity. for the entry receptor in mouse cells. »

So, it seems highly possible that at some point during 2020 the virus jumped from humans to mice, where it quickly accumulated this impressive number of mutations, and then returned to humans near the end of 2021, “indicating cross-species evolution”. trajectory of the Omicron epidemic.

If this hypothesis proves true, it would add to the evidence that hope for definitive eradication of SARS-CoV-2 becomes less and less likely as we learn more about this virus. Although animal populations remain susceptible to SARS-CoV-2 infection, there is still the possibility that the virus could spread again in humans at some point, likely in highly mutated forms. And whether these new strains turn out to be more or less pathogenic will most likely be a matter of pure luck (or bad luck), an evolutionary gamble.

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Par Andrei Ionescu, Threatened-species.fr Editor

2024-01-21 23:22:56
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