Covid-19: Canadian researchers find first possible transmission to humans from deer

Deer may be able to transmit the coronavirus virus to humans, according to preliminary research conducted by Canadian scientists monitoring the spread of the SARS-CoV-2 virus in animals.

Until now, researchers had found evidence of humans spreading the virus to deer and the animals then spreading it to other deer. But the new evidence suggests that the virus may be able to spill the other way as well.

Scientists are tracking if wild animals could become a source of new Covid-19 variants and act as a SARS-CoV-2 reservoir.

However, humans remain the primary source of the virus’ spread around the world.

The new paper was posted on bioRxiv, an online archive for unpublished preprints in life sciences. It has not been peer reviewed.

The findings stem from the work by scientists collaborating to analyse samples from hundreds of deer killed by hunters in southwestern Ontario in the fall of 2021.

The scientists discovered a highly divergent SARS-CoV-2 lineage, essentially meaning a cluster of the virus with several mutations. Around the same time, scientists identified a genetically similar virus version in a person from the same region of Ontario. The person had recently come in contact with deer.

Finlay Maguire, a collaborator on the research who helped analyse the genetic sequencing, underscored that no other human cases were found. He said in interviews reported widely in Canada that the particular case might be a red flag and didn’t seem hugely alarming.

He said the conclusions stemmed from strong circumstantial evidence.

There is a plausible link by which it could have happened — the individual involved had considerable contact with deer, said Maguire, a Dalhousie University Assistant Professor.

The research points to the need for better virus surveillance — not just among humans, but plants, animals, and the wider environment, said Maguire. Who is also a pathogenomics bioinformatics lead at Toronto’s Shared Hospital Laboratory.

BETTER SURVEILLANCE

It is still unclear how the deer caught the virus and is among the reasons Maguire called for better surveillance.

The virus might have been transmitted directly from humans, an intermediary host animal, or through wastewater.

Speaking to the state-owned Canadian Broadcasting Corporation, infectious disease physician Samira Mubareka said this version of the virus was different from the virus in circulation.

It is not closely related to the Delta or the Omicron variants. It’s most recent relative was traced to 2020, said Samira, a virologist at the Sunnybrook Health Sciences Centre in Toronto.

One of the authors of the paper, Samira said it meant that it took time for the divergent lineage to mutate.

She said, however, that it was reassuring that no evidence of further transmission was found during a time when a lot of sampling and sequencing was done.

She said further surveillance would allow them to get a better sense of the actual risk.

Previously, the other known cases of animal-to-human transmission have been in farmed mink. Some preliminary research in Hong Kong suggests that the virus might be able to spread to humans from hamsters.

CAUTION FOR HUNTERS

Most people face a higher risk of catching the virus from human contact than from deer.

The Public Health Agency of Canada (PHAC) said there was still no evidence that animals played a large role in the current Covid-19 spread. While it added that animal-to-human transmission was rare, it has warned hunters to be cautious.

Hunters and people handling wild deer have been advised to regularly wash their hands, wear goggles, gloves, and a well-fitted mask when there is the chance of being exposed to respiratory tissues and fluids, particularly indoors.

Normal cooking temperatures kill the coronaviruses and there is still no evidence that Covid-19 can spread from cooked venison.

The PHAC said National Microbiology Laboratory scientists reviewed the research findings and confirmed that the genetic similarities suggested the possibility of deer-to-human transmission.

It added that routine genomic surveillance would continue to monitor positive polymerase chain reaction test results for unusual variations in Canada.

The virus has so far been found in wild white-tailed deer in northeastern US and Canada’s Ontario, Quebec, Manitoba, and Saskatchewan.