Young white-tailed deer in the snow
A young white-tailed deer in the snow

Possible Case of Deer-To-Human SARS-CoV-2 Transmission

Canadian researchers identify a highly mutated variant of the virus in white-tailed deer and link it to a human COVID-19 case in the region—though they emphasize that the infection risk to people is low.

Catherine Offord
Catherine Offord

Catherine is a senior editor at The Scientist.

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Mar 3, 2022

ABOVE: A white-tailed deer © ISTOCK.COM, Gunther Fraulob

Update (March 22): A study published yesterday in PLOS Pathogens finds that experimentally infected white-tailed deer can shed infectious SARS-CoV-2 for five days after inoculation.

A study carried out in southwestern Ontario has identified a highly mutated variant of SARS-CoV-2 in local populations of white-tailed deer (Odocoileus virginianus) and found evidence that it might have infected a person in the area. This so-called Ontario WTD lineage, described in a preprint last week (February 25), is unlikely to present a risk to people, according to The Guardian and other news outlets, but underlines the need for better surveillance of wildlife that may act as reservoirs for the virus.

“There’s certainly no need to panic,” Arinjay Banerjee, a virologist at the University of Saskatchewan who was not involved in the study, tells The New York Times. However, he notes that “the more hosts you have, the more opportunities the virus has to evolve.”

Several studies had already identified SARS-CoV-2 in white-tailed deer populations, with researchers concluding last year that the virus was being transmitted from humans to deer as well as spreading within deer populations. Until now, however, there haven’t been any suspected cases of deer-to-human transmission.

See “Researchers Detect Coronavirus in Iowa Deer

The Ontario WTD lineage was discovered as part of a survey of white-tailed deer hunted in the province late last year. Researchers found that a little more than 5 percent of the nearly 300 deer tested were harboring the novel lineage of SARS-CoV-2. The variant is highly divergent from strains circulating in human populations, the authors note in their preprint, suggesting that it has been mutating and evolving independently for some time.

“It’s actually a pretty significant study, I think, because we’re seeing potential evolution of the virus in an animal reservoir,” the University of Guelph’s J. Scott Weese, who studies zoonotic diseases and was not involved in the work, tells CNN.

The team also linked the variant to a human COVID-19 case in southwestern Ontario. They report in their paper that the infected person, who had been in contact with deer, had a very similar strain of the virus, pointing to the animals as a probable source of infection.

Reassuringly, study coauthor Samira Mubareka tells the CBC, there is no evidence that the infected person transmitted the variant to anyone else, even “during a time when we were doing a lot of sampling and a lot of sequencing.” Mubareka, an infectious disease physician and virologist at the Sunnybrook Health Sciences Centre in Toronto, adds: “If we continue to do this surveillance, we’ll get a much better sense of what the actual risk is.”

There have been a few other animals identified as potential SARS-CoV-2 reservoirs, although reported cases of animals infecting humans are still very rare. During the first year of the pandemic, some studies indicated that people could catch SARS-CoV-2 from mink, while a preprint last month suggested that pet hamsters might also transmit the virus to people.

See “The Rise of COVID-19 Vaccines for Animals