Canadian researchers discover 1st possible case of deer spreading COVID-19 virus to a human

In a world first, preliminary research suggests deer may be able to transmit the COVID-19 virus to humans, following analysis by a team of Canadian scientists monitoring the spread of SARS-CoV-2 in animals.

Up until now, researchers have only found evidence of humans spreading the virus to deer, and deer spreading it to other deer.

New evidence suggesting the virus may be able to spill from deer to humans is a significant development, as scientists are closely tracking whether wild animals could become a source of new variants and act as a reservoir for SARS-CoV-2.

Still, humans remain the main source of the virus and its spread around the world. 

The new research paper posted Friday on bioRxiv, an online archive and distribution service for unpublished preprints in the life sciences, has not been peer reviewed. 

The findings stem from work by a team of scientists who collaborated to analyze samples taken from hundreds of deer killed by hunters in the fall of 2021 in southwestern Ontario.

In their analysis, scientists discovered a highly divergent lineage of SARS-CoV-2 — which essentially means a cluster of the virus with a lot of mutations.

Around the same time, a genetically similar version of the virus was identified in a person from the same region of Ontario who had recently been in contact with deer.

Finlay Maguire, who collaborated on the research and helped analyze the genetic sequencing, underscored the fact no other cases were found in humans.

"This particular case, while raising a red flag, doesn't seem to be hugely alarming."

He said their conclusions come down to strong circumstantial evidence.

"While we haven't seen [transmission from deer to human] 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," Maguire 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."

The research points to the need for better surveillance of the COVID-19 virus — not just in humans, but also in animals, plants and the wider environment, said Maguire, an assistant professor at Dalhousie University and a pathogenomics bioinformatics lead at Sunnybrook Health Sciences Centre in Toronto.

How the deer caught the virus in the first place is unclear, which is one of the reasons Maguire and others say more surveillance is needed.