Covid-19: First proven transmission from deer to humans

Could a deer be the source of the next variant of the coronavirus? Many mammals can be infected with the virus responsible for Covid-19, hosts in which the virus can develop and develop variants that can then re-infect humans. But so far, transmission back to humans has only been observed in a small number of these animals, including mink And hamster, which led to mass carnage to avoid these transfers. But to these potential sources of new variants, a new group of mammals, the deer, can be added.

The virus has accumulated dozens of mutations in deer

In August 2021, US authorities stressed that almost half of deer in North America could have contracted Covid, which was the first detection of mass infection with coronavirus in wild animals. This high infection rate showed that the coronavirus appeared to be very easily transmitted among deer (which do not develop serious illness once infected), but it was not yet certain that deer could retransmit the virus to humans. This uncertainty was removed on February 25, 2022. preprint (scientific article not yet peer-reviewed) published by the Canadian Center for Animal Diseases. According to this study, the coronavirus has already been transmitted at least once from deer to humans.

Canadian researchers analyzed samples of 300 white-tailed deer (Odocoileus virginus) in the Canadian province of Ontario during the hunting season from November to December 2021. Among these deer, the presence of coronavirus was confirmed in 21 samples (6% of the total number of deer in the study). With these samples, the researchers were able to reconstruct five complete genomes of the virus, as well as two partial ones. Prior to this study, all virus sequences found in deer were very close to those that were simultaneously present in humans, indicating that the virus did not have time to evolve in its new hosts. But these five genomes, very similar to each other, were very different from the rest of the variants currently circulating in humans, with 76 mutations compared to the sequence of the original coronavirus strain.

At least one transmission to a person

Their analysis also revealed a genomic sequence of the virus very close to that found in deer (which have the vast majority of these mutations) in a human living in Ontario. This person became infected in the fall of 2021 and had direct contact with deer shortly before infection.

But no other human sample showed these mutations, and the closest genomic sequence was found a year earlier in Michigan, with less than half of these genetic variations. Therefore, it is likely that this new variant comes from a coronavirus that was transmitted to deer a year ago in North America, where it would have evolved over a year, accumulating 49 mutations, before returning to humans.

But these mutations do not seem to pose a threat to humans.

Nine of the 76 mutations found in deer and infected humans in Ontario are in the coronavirus spike protein, six of which result in at least one amino acid change. This raised concerns that this new variant might elude antibodies that recognize this protein. Fortunately, analysis of the plasma of vaccinated people has shown that their antibodies have no problem recognizing and neutralizing this variant. Thus, these mutations do not affect the effectiveness of current vaccines.

Indeed, the researchers found that the ratio of nonsynonymous mutations (which change an amino acid) to synonymous mutations is very low, suggesting there was no selection pressure for the coronavirus in deer. Thus, these mutations are probably neutral, i.e., they do not represent an advantage for the virus. This lack of selection pressure could be explained by the weak (or even absent) acquired immunity to other coronaviruses in deer, which become less ill after infection, allowing the virus to be transmitted unhindered, which accumulates neutral mutations between each passage. from one deer to another.

However, the authors warn that if the dangerous variant ever appears in wild animals such as deer, it will be much more difficult to control than in farmed species such as hamsters and minks. However, there is no further evidence of deer-to-human or human-to-human transmission of the deer variant of the coronavirus. So at this point it seems unlikely that the next worrisome option comes from these animals, but we still have to remain vigilant.

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