Humans are the main source of COVID-19, but what happens now that we've spread it to animals?

If there's one thing social media loves, it's a Disney-like moment with a wild animal. There's the much-loved video with the golden retriever who's best friends with a deer, or the one where a woman hand-feeds deer on her porch. But those seemingly innocent interactions between humans and wildlife could be costly during a pandemic.

Humans are currently the main source of transmission for the virus that causes COVID-19, SARS-CoV-2. Globally, the virus has been found in 19 different species, mostly animals that are domestic or living in captivity.

What concerns scientists is the potential for another species to become a reservoir. If SARS-CoV-2 circulates widely enough in another species, there's a risk that animal could become a potential source for new variants and transmission back to humans.

While so far there's no evidence of that happening in the wild, the cycle of transmission seen on mink farms in Denmark, where mink infected by workers spread a new variant back to workers, is exactly the type of situation infectious disease experts want to avoid.

So far, the only known cases of SARS-CoV-2 in the wild were found in mink and deer. Most of the mink that have been infected were on fur farms, but a wild mink did test positive in Utah, in an area where there were outbreaks on local farms.

Until recently, most conversations about animals and COVID-19 had to do with its origins, said Scott Weese, an infectious disease veterinarian and a professor at the University of Guelph's Ontario Veterinary College.

He's one of many experts saying that kind of thinking to change to more of a holistic approach, one that considers how all species are interlinked. 

"We had to really kind of drag people kicking and screaming to pay attention to animals," Weese said. 

"We don't have people and everything else. We're all in this big ecosystem." 

People should be aware of the risk of animal transmission, but not worried, he said. At this stage of the pandemic, the average person poses a greater risk to other animals than animals pose to people, and people are far more likely to be exposed to the virus from another person than an animal. 

But the last thing we want to do is gain control of the virus in humans only to discover another species has become a reservoir, he said.

"The risk of variants emerging in the human population will get lower as we vaccinate everyone, if we vaccinate the world. So if we do that, the biggest pool of susceptible individuals and the biggest pool for circulating virus may be wildlife," he said. 

At Toronto's Sunnybrook Health Science Centre, infectious disease physician and virologist Dr. Samira Mubareka has been working with her team to analyze samples taken from white-tailed deer killed by hunters.

Together with the Canadian Food Inspection Agency's National Centre for Foreign Animal Disease, they analyzed the entire genome sequence of the virus found in Quebec deer and identified the Delta variant.