The researchers analyzed 454,443 SARS-CoV-2 genes and 14,427 genome-wide sequences collected from around the world. They were unable to find traces of the early evolution of the “British” strain in viral samples from humans. However, after they expanded their search to include animals, they found some early forms of B.1.1.7 in dogs, including in one sample taken from the United States last July.
“Such progenitor variants included most or all of the early B.1.1.7 mutations in populations of the Canidae (canine) family, and they may have returned to humans after a period of rapid mutation,” the study authors wrote in an article that peer reviewed and published as a preprint.
The “British” variant has nine different mutations that scientists say were rarely found in earlier human lines, and perhaps never.
These mutations did not occur in neighboring genes, but spread throughout the viral genome. The likelihood of all these mutations occurring at the same time is extremely small, and the authors of the study believe that they arose one after the other. In their opinion, this variant could appear outside the UK and acquire mutations on the animal. Among the possible “suspects”, scientists also named the families of mustelids (minks, ferrets, otters, etc.) and felines.
According to the deputy. the head of the scientific and educational center of the FGBNU FITSViM, a specialist in infectious animal diseases Timofey Sevskikh, the hypothesis of Chinese scientists has a strong evidence base and may be the most likely variant of the appearance of the “British” variant of the virus. Cases of transmission of the virus from cats or dogs to humans have not been recorded, since a single animal taken releases too little virus into the environment to infect humans. Cases of animal-to-human transmission of the virus have been mainly associated with fur farms, where infection of large numbers of animals in an indoor environment creates a high viral load sufficient to infect humans.
“This study showed that mutations of the virus acquired during passage through the body of dogs contributed to an increase in its virulence, while reducing its replication. This means, firstly, that infection requires a smaller dose of viral particles than the original version. Secondly, due to a decrease in the replication rate, the infectious process can develop longer, which is why the affected individual can release the virus into the environment for a longer time, ”the expert told MedPortal Sevskikh. According to him, when a virus enters a large population – for example, in a dog nursery – the likelihood of infection increases significantly.
“Thus, the WHO recommendation to minimize contact with pets in case of detection of COVID-19 takes on new meaning,” the scientist said.