First Possible Case of Covid-19 Spreading From Deer to Humans

Scientists in Canada have discovered the first potential case of deer passing coronavirus to a human, according to the new research that hasn’t yet been peer-reviewed. The event has raised new concerns that wildlife could host Covid-19 strains that could eventually spill over to humans.

The team also identified new, highly-mutated strains of Covid-19 in white-tailed deer, highlighting the potential dangers of wildlife hosting the virus. Like humans, animals can act as reservoirs for a pathogen as it spreads and mutates—sometimes into a more deadly or contagious version of itself.

In their study, the Canadian scientists collected samples from the noses and lymph nodes of hundreds of white-tailed deer hunted in southwestern Ontario last fall. Their analysis revealed that 17 of the 298 deer they tested were positive for a “new and highly divergent lineage” of the coronavirus, per the Guardian’s Leyland Cecco.

When researchers compared the “highly divergent” version of Covid-19 to human cases, they found a person with a similar strain, indicating the virus jumped from deer to humans. The infected person lived in southwestern Ontario and had close contact with deer, Rachael Rettner reports for Live Science. The study was released last week on the preprint server bioRxiv and is awaiting formal review.

The discovery underscores the importance of monitoring wildlife for diseases that could jump to humans but isn’t yet cause for panic. 

“This particular case, while raising a red flag, doesn’t seem to be hugely alarming,” says Finlay Maguire, one of the study authors and an epidemiologist at Dalhousie University in Nova Scotia, to Jaela Bernstien for CBC News.

Before researchers identified the recent case, scientists weren’t sure humans could get Covid-19 from white-tailed deer. Typically the virus spreads from humans to deer (and then deer to deer), not the other way around. Scientists aren’t sure how deer originally contracted the virus from humans, but suspect it could have been spread through water, food, other animals, or close contact with people.

The recent Covid-19 lineage identified in the study isn’t related to the Delta or Omicron variants, per Carolyn Crist for WedMD. Instead, Maguire notes that the closest genetic relative came from samples taken from humans and mink in Michigan two years ago. 

Based on the lineage’s specific mutations, researchers behind the work believe that existing Covid-19 vaccines are still effective at preventing serious disease and death. So far, the recent human case seems to be an isolated incident, though the Public Health Agency of Canada has issued new guidance for those that come in close contact with deer.

“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,” says Samira Mubareka, a microbiologist at Toronto's Sunnybrook Health Sciences Centre who was involved in the study, to CBC News. “If we continue to do this surveillance, we’ll get a much better sense of what the actual risk is.”

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Corryn Wetzel is a freelance science journalist based in Brooklyn. Her work has also appeared in Audubon magazine, National Geographic and others.