Question: I read in the news that the Omicron variant has been found in wild deer. What does this mean for the future of the COVID-19 pandemic?
Answer: Researchers have long known that SARS-CoV-2, the virus that causes COVID-19, can infect some animals, including household pets, farm livestock and wildlife such as white-tailed deer.
The main concern is that the virus could establish itself in animal populations, where it would continue to mutate and potentially produce new variants.
“Once the virus goes into an animal, the selective pressures on it are going to be quite different, and it may change in unpredictable ways,” said Vikram Misra, a professor of microbiology at the University of Saskatchewan.
“And if the virus comes back into the human population, it’s impossible to say how virulent it might be or whether it will be neutralized by the immunity we have acquired through vaccinations and previous infections,” he added.
“There are a lot of big unknowns.”
Regardless of whether the virus is infecting a person or an animal, it generally uses the same approach. Spike proteins – knobby protrusions on the virus – latch onto ACE-2 receptors on the surfaces of cells.
The ACE-2 receptors serve as gateways into cells and differ between species. That means the virus may not always be able to effectively bind onto the ACE-2 receptors of certain creatures. So in some animals the virus enters cells with relative ease, while in others it is blocked.
However, over the course of the pandemic, some of the newer variants have evolved with the ability to infect more types of animals.
For instance, the original version of the novel coronavirus first identified in Wuhan, China, was not able to invade mouse cells, noted Angela Rasmussen, a virologist with the Vaccine and Infectious Disease Organization at the University of Saskatchewan.
“But Alpha, Beta, Gamma and Omicron variants all have a mutation in the spike protein that allows the virus to bind and infect mouse cells,” she said.
As a result, the virus now has more animals in which to flourish.
In a paper that has not yet been peer reviewed, some scientists speculate that the highly infectious Omicron variant, which contains many mutations, may have emerged from a rodent.
Dr. Misra said the paper doesn’t provide conclusive proof and we may never learn the real origins of Omicron.
But there is at least one well-documented example of the virus jumping back and forth between people and animals, said Samira Mubareka, an infectious diseases physician and virologist at Sunnybrook Health Sciences Centre in Toronto.
She points to mink farms in Demark, where the animals are raised in close quarters. Workers infected with SARS-CoV-2 spread the virus to the captive mink. Once in the animals, the virus mutated and got transmitted back to the workers. “Luckily, that variant burnt out – it didn’t go any further,” Dr. Mubareka said.
Even so, the case illustrates the need for ongoing monitoring of potential sources of new variants in animals.
Dr. Rasmussen is part of the Coronavirus Variants Rapid Response Network (CoVaRR-Net), a federally funded group of researchers sharing data from across Canada.
“One of our main objectives is to understand which species are susceptible in Canada and which of those species are then likely to interact with people,” she explained.
Researchers have also been trying to collect viral samples from animals using existing programs for monitoring diseases in wildlife populations, said Dr. Mubareka, who is also part of CoVaRR-Net.
During hunting season, deer carcasses are routinely checked for a condition known as chronic wasting disease. From such a program last year, researchers were able to obtain nasal swabs that confirmed white-tailed deer in Quebec were infected with COVID-19.
Since then, the virus has been identified in deer in other Canadian provinces. And it is widespread in deer populations in numerous U.S. states.
Experts aren’t sure how the deer were originally infected, but it could be happening on a continuing basis when people encounter the animals, Dr. Misra said.
Of course, there’s a theoretical risk that deer could now infect people. Hunters, in particular, are being urged by public-health officials to use safety precautions when handling an animal carcass, such as wearing a mask, following proper sanitation procedures and, possibly most important, getting vaccinated.
The virus affects animal populations in different ways. Deer show no outward signs of illness, whereas mink can become extremely sick and even die, Dr. Mubareka said.
In the case of domestic pets, cats appear to be more likely than dogs to contract COVID-19 from their owners. And cats seem to be quite capable of spreading the infection to other felines. So far, though, there have been no reports of people catching the virus from their pets. But that’s not necessarily a reason to completely let down your guard.
“Just because we haven’t had a report of it happening yet doesn’t mean that it couldn’t potentially happen in the future,” Dr. Rasmussen said. The virus, she noted, continues to evolve and change.
For that reason, people should try to protect their pets from infection. “If I got COVID, I wouldn’t nuzzle up as closely with my dog as I normally do – for her safety as well as my own,” she added.
Meanwhile, researchers are facing the huge task of trying to identify potential animal reservoirs of the virus and developing mitigation strategies to prevent people from being infected with new variants.
“We have just begun to scratch the surface in terms of what needs to be done,” Dr. Mubareka said. But she is equally concerned that a lot of focus on finding potential reservoirs in animals will create the wrong impression among the public.
“It’s important not to think of these animals as a threat. In fact, the opposite is true. We are threatening them,” she said.
Human activities, she noted, are shrinking and fragmenting environments where wild animals normally reside.
“We are encroaching on their habitats and surrounding them in ways that increase the interface between people and animals.”
Right now, the virus is primarily spreading within the human population. “There is just so much more of the virus circulating in humans than in animals,” she added.
If we want to minimize the risk of COVID-19 spilling over into wildlife populations, then “the best thing we can do is reduce the amount of viral disease in people.”
Paul Taylor is a former patient navigation adviser at Sunnybrook Health Sciences Centre and a former health editor of The Globe and Mail.
Paul Taylor