It looks like SARS-CoV-2, the virus that causes COVID-19, may have possibly jumped from a deer to a human in Canada, according to a new pre-print paper. 

Last year, numerous research teams noticed that the coronavirus was spreading like wildfire among certain populations of white-tailed deer in North America. While some scientists speculated deer-to-human transmission may be a possibility, they were yet to find any evidence. 

Now, scientists in Canada argue they have found a potential human case of COVID-19 that can be traced to a strain of the virus found in deer, indicating that deer-to-human transmission has occured. The evidence, which is yet to be peer-reviewed, was recently posted on the preprint server bioRxiv.

The team of researchers tested the nose and lymph nodes of almost 300 deers that had been hunted in Southwestern and Eastern Ontario in 2021, of which 17 tested positive for SARS-CoV-2. 

Most worrying of all, the strain found in the deers appears to have some strong genetic differences from the strains currently circulating in human populations. The team noticed 76 mutations from the initial Wuhan strain of SARS-CoV-2, including 37 previously found in non-human animal hosts, 23 of which were not previously reported in deer. This distinctive strain was then seen in a human case reported in the same geographic region and sampling period.

It’s not totally clear how the virus managed to leap from a deer to a human. Certainly, direct deer-to-human transmission is a possibility, perhaps through hunters coming into contact with the animals, although the researchers also say an intermediate host animal may be involved, such as a farmed or wild mink. This is because the closest relative to the deer strain is similar to the strain found nearby in Michigan back in 2020. 

Regardless of the precise route of transmission, the possibility of deer-to-human transmission is worrying for a couple of reasons. Firstly, it raises the possibility that deer and other animals could act as a natural reservoir for the virus, silently harboring the infection and sparking new human outbreaks of COVID-19 in the future. Most pressingly, these new findings indicate that deer may be acting as a refuge for the virus that could possibly foster the creation of new variants.

Fortunately, the researchers claim there’s no evidence of recurrent deer-to-human transmission at this time, suggesting this could be just a one-off. With that said, the team also say they can not rule out the possibility of onward transmission from the human case to other people. 

Above all, they argue this discovery highlights the need for public health agencies across the world to closely monitor the emergence of new mutations in both human populations and non-human animals. 

Off the back of this new preprint, Canada’s public health authority states this “appears to be an isolated case with no further transmission,” adding that “animal-to-human transmission is likely very uncommon.”

“Until we know more, people who hunt, trap or work closely with or handle wildlife should take precautions to prevent the potential spread of the virus,” the agency said on its website.