Deer Caught COVID-19 From People, Study Shows, But Questions Loom

ACROSS AMERICA — White-tailed deer are likely contracting the coronavirus from humans and rapidly spreading it among themselves, according to a new study that found up to 80 percent of deer sampled in Iowa were infected with COVID-19.

The study by Iowa wildlife officials working with veterinary microbiologists from Penn State University raises troubling questions about the spread of coronavirus, which has been found in deer populations in multiple U.S. states, from one coast to the other.

The study’s authors weren’t able to answer the critical question of how the coronavirus spread to deer from people. They said there is no evidence to show the virus has jumped from deer back to humans, citing the need for more research to determine if that can happen — and, if it can, if it the virus will mutate to a more dangerous strain.

Although the researchers focused on deer in Iowa, they said there is no reason to think the same thing isn’t happening in other states with white-tailed deer populations. White-tailed deer are widely distributed across the United States, with the total population estimated at 38 million.

With almost half a million white-tailed deer roaming Iowa, there are plenty of opportunities for people to have passed the coronavirus to deer, Dr. Rachel Ruden, the state wildlife veterinarian and one of the study’s authors, told The New York Times.

Some possibilities include backyard feeding, sewage discharges or even an animal licking a plug of chewing tobacco spat by an infected hunter.

“Perhaps it doesn’t take much of a loading dose to get deer infected,” Ruden told The Times. “But either way, all of this is a striking example that we’re all in this pandemic together.”

To determine active coronavirus infections in deer, the veterinary microbiologists from Penn State University examined the lymph nodes of samples of roadkill and deer harvested by hunters from March 2020 to January 2021, during the height of the pandemic.

The researchers noted the greatest increases in active COVID-19 infections in deer coincided with the peak of deer hunting season in Iowa last year.

And though their study hasn’t been published in a peer-reviewed journal, the authors were alarmed enough by their findings to warn deer hunters and others to wear personal protective equipment when handling deer carcasses and processing meat, and to get vaccinated against COVID-19.

The study provides the first direct evidence of the COVID-19 virus in any free-living species.

“Our findings have important implications for ecology and long-term persistence of the virus,” Suresh Kuphipudi, one of the lead researchers, said in the news release.

“These include spillover to other free-living or captive animals and potential spillback to human hosts,” Kuphipudi said. “Of course, this highlights that many urgent steps are needed to monitor the spread of the virus in deer and prevent spillback to humans.”

The lead researchers told The New York Times they were surprised COVID-19 infections in deer were so widespread in Iowa, and that there’s no reason to think the same thing isn’t happening in other states with deer populations.

“It was effectively showing up in all parts of the state,” Kuchipudi told The New York Times. “We were dumbfounded.”

An earlier study showed two-thirds of deer in four states — Michigan, Illinois, New York and Pennsylvania — have COVID-19 antibodies. That study, by the U.S. Department of Agriculture’s Animal and Plant Health Inspection, turned up antibodies for the virus. The researchers emphasized the findings indicated exposure, not an active infection, but also said the presence of antibodies could mean the deer fought off the infection.

Scientists reacting to the findings emphasize more research is needed to determine if deer, or other animal populations, can pass the virus back to humans, or how the virus might mutate.

The risk of animal transmission is considered low. But it does happen. In late 2020, millions of farmed minks were slaughtered in Denmark after about a dozen people were infected with a strain of coronavirus found in the animals.

Tony Goldberg, a veterinarian at the University of Wisconsin-Madison who was not involved in the study, told The Times it would be “game changer” if the virus could jump from deer to people.

“If deer can transmit the virus to humans, it’s a game changer,” said Tony Goldberg, who studies the evolution of infectious diseases as they jump between animals and people. “To have a wildlife species become a reservoir after transmission from humans is very rare and unlucky, as if we needed more bad luck.”

Scientists are keen to look at how the virus behaves in other species, including rodents that live in close proximity with people, and whether it will mutate to more dangerous levels.