Coronavirus may be widespread in white-tailed deer; it could mutate and spread to humans and other animals

A researcher swabs a white-tailed deer's saliva. (New York Times photo by Sergio Flores)

Evidence suggests the novel coronavirus may become entrenched in the white-tailed deer population. That could give the virus much more opportunity to mutate and spread to other animals, including humans, Emily Anthes and Sabrina Imbler report for The New York Times. "If deer were to become established as a North American wildlife reservoir, and we do think they’re at risk of that, there are real concerns for the health of other wildlife species, livestock, pets and even people," said Dr. Casey Barton Behravesh of the Centers for Disease Control and Prevention. "This is a top concern right now for the United States." Behravesh directs the CDC's One Health Office, which focuses on connections between human, animal and environmental health.

"From the start of the pandemic, experts were aware that a virus that emerged from animals, as scientists believe SARS-CoV-2 did, could theoretically spread back to animals. Mink have garnered much attention after the virus spread through mink farms in Europe and North America, leading to massive culls of the animals. But white-tailed deer, which may wander into urban and rural backyards, are also easily infected," Anthes and Imbler report. "Infections in free-ranging deer, which display few signs of illness, are tricky to detect and difficult to contain. Deer also live alongside us in dizzying numbers; about 30 million white-tailed deer roam the continental United States."

Scientists knew mammals, especially deer, would be more susceptible to infection from the beginning of the pandemic; the coronavirus enters cells by attaching to a certain kind of receptor, and many mammals have close cousins of that receptor, Anthes and Imbler report.

Evidence has borne out the theory. In December 2020, scientists analyzed more than 4,000 dead white-tailed deer in Iowa and found that more than 60 percent were infected. And in July, when the federal Animal and Plant Health Inspection Service sampled blood from deer in Illinois, Michigan, New York and Pennsylvania, 40% had coronavirus antibodies (which meant they likely had already been infected), Anthes and Imbler report. Scientists in Ohio, Texas, Ontario, Quebec and Saskatchewan have found similar results.

"Whether the virus makes deer sick remains unknown. There is no evidence that infected deer become seriously ill, but humans might not notice if a wild animal was feeling slightly under the weather," Anthes and Imbler report. Stephanie Seifert, a zoonotic diseases expert at Washington State University, told the Times that, while scientists know many deer have been infected and spread the virus, they're not sure how humans (or other animals) are infecting the deer, how the virus is adapting or what will happen next. Knowing those things, especially how the deer are getting infected, is critical for risk assessment, so scientists are researching it.