According to a prepublished study, a white-tailed deer (Odocoileus virginianus) allegedly transmitted the coronavirus to a resident of Ontario, Canada. This would be the first case of interspecies transmission involving a white-tailed deer, a species found across North America.
Thanks to previous work, we already knew that the virus circulated widely among American white-tailed deer populations. But before this new study came out, their virus looked like the one contracted by humans living nearby. So it was easy to believe that we are the ones who are infecting the deer, and not the other way around.
But recently, a Canadian team of 32 government and university researchers concluded, in a publication published in BioRxiv, that in 2021, more than a dozen Canadian white-tailed deer were infected with a coronavirus with a constellation of “never-before-seen mutations in SARS-CoV-2 lineages.”
At the same time, further analysis showed that an Ontario resident who was in direct contact with a white-tailed deer was infected with the same variant. (This screening was made possible thanks to the government’s campaign to sequence all Covid-19 cases occurring in the region at the time.)
Together, these parameters indicate that the virus would have circulated among deer and would have accumulated mutations as it passed from one animal to another before being transmitted to humans. It is possible that the virus first passed through another host species, such as mink, although, according to the authors, genomic analyzes indicate that transmission from deer to humans is “the most likely scenario”.
According to several experts, this pre-publication should not cause concern.
According to Jüergen Richt, a veterinarian and director of the Center for Emerging Infectious and Zoonotic Diseases at Kansas State University, the likelihood of transmitting the virus between humans remains much higher than catching it through contact with a deer. Furthermore, Jüergen Richt did not intervene in this prepublished study.
PCR TESTS FOR DEER
As part of their research, scientists collected nasal and tissue samples from 300 white-tailed deer killed in southwestern and eastern Ontario between November and December 2021. All were shot by hunters and were already being tested as part of an annual program. of sorting. for the chronic wasting disease (EC) that can kill deer and their close cousins. Some of the samples tested were illegible, but the researchers found that 17 of 298 deer (or 6% of the population studied) tested positive for a “new and highly divergent variant”.
Surprisingly, their results show that this variant is an old version of Covid, predating the Delta and Omicron variants. The coronavirus would therefore be circulating in deer for a long time.
After conducting their screening campaign, the study authors performed analyzes to assess the vaccine’s potential for vaccine leakage from this virus that affects deer. They concluded that current vaccines likely provide robust protection against it.
This is good news according to Jüergen Richt, who also believes that the hypothesis of a direct infection from deer to humans is the most likely explanation for the origin of the infection found in an Ontario resident.
However, he draws attention to the fact that there are likely other variants not listed in humans as well as animals. And the picture may be even more complex than we think.
“As a scientist, you always have to ask yourself what else can happen when you’re not 100% sure,” he recalls.
The research team points out, however, that it is not yet known whether other humans have been infected with this virus of deer origin or if there have been other cases of interspecies transmission from deer to humans.
“With the emergence of Omicron and the end of the deer hunting season, [les possibilités] for genomic screening and surveillance in humans, as well as in [cerfs de Virginie] are restricted to that region from the time these samples were collected,” the researchers write in their paper.
CASES IN MINKS AND HAMSTERS
During the pandemic, several humans were infected by farmed mink and an employee at a pet store in Hong Kong was infected with a hamster (as a result, all hamsters in the store were killed and the government required hamster keepers to hand them over authorities for euthanasia). The researchers note that, unlike these isolated cases involving domestic animals, it is much more difficult to monitor (and detect) transmission between white-tailed deer and humans.
It is also unknown how these deer may have become infected with the coronavirus. as explained National Geography in August 2021, may be due to the research teams, nature conservation, tourists and hunters they encounter.
At the time, researchers from the United States Department of Agriculture (USDA) speculated that the deer may have become infected with the virus by drinking contaminated sewage or exposing themselves to other infected species, such as the mink.
USDA did not respond to our requests for this article.
In early 2021, USDA researchers detected antibodies against Covid in 40% of white-tailed deer tested in Michigan, Illinois, New York State and Pennsylvania. According to their work, these animals were in contact with the virus, but none showed symptoms. Later studies revealed that other deer had been infected, particularly in Iowa. According to Jüergen Richt, it is now possible for the virus to “circulate widely” in the United States among the animal population.
According to the research team, it is “particularly important” to increase surveillance of human and animal populations and, more particularly, deer populations.
“At this time, there is no evidence of recurrent deer-to-human transmission or recurrent human-to-human transmission,” the researchers said.
They add that it is crucial to identify the species in the reservoir that could be the source of prolonged transmission of the virus or interspecies infection.
“I think this study will be a milestone,” says Tracey McNamara, an animal pathologist at Western University of Health Sciences in Pomona, California. She hopes that “this is the future of biomonitoring, that we have to look at the spectrum of the animal kingdom as a whole, and not just separate humans, separate animals, but that we do this work together. That’s what this band has done, and is quite remarkable. »