The omicron variant of Covid-19 may have originated in mice

According to a study by the University of Minnesota, in the United States, the variant omicron of Sars-cov-2 it may have originated in mice. The researchers, in fact, studied the numerous mutations in the spike protein of the variant still dominant globally, finding that one of these would be compatible with both a receptor of human cells with either one of the mouse cells, while others two mutations would only be compatible with the mouse receptor: these characteristics could be justified of the transmission of a variant of Sars-cov-2 from humans to the mice, its evolution into omicron and its subsequent return to humans. The results of the study were published in the journal Pnas.

Omicron continues to spread – and to mutate

The variant emerged at the end of 2021 and spread rapidly globally omicron continues to be dominant in all countries of the world. Moreover, as time goes by, his own emerge sub-variantssome of which appear to be more infectious and escape better to the immune system of the guest. As reported by ainvestigation coordinated by the Higher Institute of Health (Iss) in Italy, according to data updated to 4 October last, omicron had a prevalence estimated at 100%, with the sub-variant Ba.5 (called omicron 5, which spread from February 2022 and which we have talked about here) largely predominant. Not only that: according to the Centers of disease control and prevention (CDC), two sub-variants deriving from Ba.5 (called Bq.1 and Bq.1.1), accounted for about 11% of infections in the United States as of October 15, while less than 1% the month before, suggesting their high infectivity; meanwhile, the usual update epidemiological report of the World Health Organization (WHO), published last October 19, reported the presence in 26 countries of the world of xbb, a recombinant of the omicron sub-variants Ba.2.10.1 and Ba.2.75 with 14 additional mutations in the spike protein; according to the health organization, which was based on preliminary laboratory tests, the latter would be the variant of Sars-cov-2 best able to escape from antibodies.

The study and the results

In light of this, monitor dissemination And the origin of the variants of an infectious agent is essential to contain it and prevent any future epidemics; for this reason, in the case of zoonoses such as Covid-19, it is also crucial to study the animal reservoirs that can host the viruses and their variants, in order to understand betterevolution. Regarding Sars-cov-2, there is no definite evidence on the origins of the omicron variant, but a method to investigate them (which has also proved useful in the study of the animal origin of Sars-cov-1, the agent responsible for the Sars) is analyze the portion of the spike protein – which in omicron has more than 50 mutations compared to the original strain – which interacts with Ace receptors, contained in both humans and mice, and that through this bond mediates the entry of the virus into host cells. Studying the adaptations of the spike structure to the Ace receptor based on the different animal species (in this case humans and mice, considered, as we read in the study, two possible sources of the omicron variant) can provide very useful information on evolution and origins of the virus.

In fact, the researchers focused on four mutations typical of omicron surrounding the region of interaction with the Ace receptor, finding that all would be the fruit of adaptations of the spike structure to the Ace receptor of mice: in particular, while three of them are uniquely compatible with the protein of mice, one would have adapted to both the human and the murine receptor. L’hypothesis advanced by the researchers would, therefore, be that a variant of Sars-cov-2 containing the mutation adapted to humans and mice could have been transmitted by humans or from another animal species to mice. Later, when this began to spread in rodents, mouse-specific mutations have evolved (like the three analyzed by the researchers) that they have contributed to the emergence of the omicron variantwhich then returned to infect humans, spreading rapidly and soon becoming the dominant variant of Sars-cov-2.