Typically, humans spread the virus to deer, and then deer spread it to other deer. But new evidence suggests that the virus could spill over from deer into humans. The researchers identified a COVID-19 case in someone from Ontario who had recently been in contact with deer.
“This particular case, while raising a red flag, doesn’t seem to be hugely alarming,” Finlay Maguire, PhD, one of the study authors and an epidemiologist at Dalhousie University, told CBC News.
“While we haven’t seen [transmission from deer to humans] happen directly, we sampled from the human case around the same time we sampled from the deer, and we sampled from around the same location,” he said. “There is also a plausible link by which it could have happened, in that the individual involved is known to have had considerable contact with deer.”
Maguire and colleagues have been monitoring the spread of the coronavirus among animals. They analyzed nasal swabs and lymph node samples taken from hundreds of deer that were killed by hunters in fall 2021 in southwestern and eastern Ontario. Among 298 sampled deer, 17 tested positive -- all from southwestern Ontario.
During the analysis, they found a “highly divergent” coronavirus lineage, which means a cluster of samples with many mutations. Around the same time, they found a genetically similar version in a person from the same region.
The study points to the need for better surveillance of the coronavirus, Maguire told CBC News, including in humans, animals, plants, and the broader environment. Researchers aren’t quite sure how deer contract the virus from humans, but it could happen through contaminated water, direct contact, food, farming, or other animals such as mink.
The coronavirus lineage identified in the study is different from what’s circulating among humans now, and it’s not related to the Delta or Omicron variants. The closest genetic relative came from samples taken from humans and mink in Michigan in 2020, which means the divergent lineage mutated and evolved over time.
“It’s reassuring that we found no evidence of further transmission, during a time when we were doing a lot of sampling and a lot of sequencing,” Samira Mubareka, MD, one of the study authors and a virologist at Sunnybrook Health Sciences Centre, told CBC News.
“If we continue to do this surveillance, we’ll get a much better sense of what the actual risk is,” she said.
So far, the coronavirus has been found in wild white-tailed deer in the northeastern U.S. and central Canadian provinces.
Other known cases of transmission from animals to humans have been identified in farmed mink and potentially hamsters, the news outlet reported. But for the most part, humans transmit the virus to animals and are most likely to catch the virus from other people.
At the same time, the Public Health Agency of Canada has issued guidance for hunters, trappers, and those who handle wild deer. People should wear gloves, goggles, and a mask when they could be exposed to respiratory tissues and fluids, especially indoors.
Coronaviruses are killed by normal cooking temperatures, the agency said, and there has been no evidence that cooked venison can spread the virus.