The main assumption of Chinese researchers is that the mouse has somehow been infected with the SARS-CoV-2 virus by the so-called reverse animal transfer. All (or most) mutations in the S protein developed in the rodent’s body and then the pathogen transferred back to humans. This theory is bold, but it explains why Omicron so different from the earlier SARS-CoV-2 variants.
There is a problem though: mouse ACE2 receptor homolog (hACE2), which SARS-CoV-2 uses to penetrate the human body, has a low affinity for the S protein of the coronavirus. Simply put: SARS-CoV-2 attacking humans should not spread to mice.
The Omikron variant seems to be on the way into different types of cells in the respiratory system. These can include bronchial and alveolar epithelial cells, as well as alveolar macrophages and various types of pneumocytes. There is a theory that the Omikron does not need to connect to ACE2 for penetration into cells, and prefers direct uptake by endosomes. In other words: SARS-CoV-2 did not need human ACE2 receptors to reach the body of mice.
If the Omicron did evolve in the rodent organism, it should be able to be tested for the analysis of his DNA. A species-specific molecular spectrum of mutations should be detectable. Unfortunately, in practice it is not that easy.
Molecular spectrum of Omicron mutations it differs significantly from any other virus that spreads among humansand resembles the spectra associated with the evolution of viruses in mouse cells. Hence, there were suggestions that Omikron was created even after a short stay in an intermediate host – a mouse, a rat or a deer.
If the Omicron is indeed descended from mice, what kind of rodent was it? Are we talking about a wild mouse or a laboratory mouse? There is no clear answer to this question, but further research should shed new light on the Omicron’s origins.