According to the U.S. Department of Agriculture, which led the research project, humans transmitted the virus to deer at least 100 times. The virus then spread widely among free-ranging deer populations, and there were three possible cases of the deer transmitting the virus to humans.
The data comes from tests done between November 2021 and April 2022 on more than 12,000 deer found across half of the United States. Sequencing of the virus found in the deer showed that deer had been exposed to all of the prominent variants, including Alpha, Gamma, Delta, and Omicron.
Some of the findings about transmission were published in the journal Nature Communications, in which researchers noted that in addition to being identified in deer, the virus has been found in wild and domestic animals, including mink, rats, otters, ferrets, hamsters, gorillas, cats, dogs, lions, and tigers. Animal-to-human transmission has been documented or suspected in mink and domestic cats, in addition to white-tailed deer.
The findings are important because the animal populations can become “reservoirs ... in which the virus circulates covertly, persisting in the population and can be transmitted to other animals or humans potentially causing disease outbreaks,” according to the paper, which was a collaboration among scientists from the U.S. Department of Agriculture, CDC, and the University of Missouri–Columbia.
In the three cases of possible deer-to-human transmission, researchers said that mutated versions of the virus previously found only in deer had been found in COVID test samples taken from one person in North Carolina and two people in Massachusetts. Those deer-specific mutated versions of the virus have not been found in any other human samples, lending evidence that the mutations occurred within deer.
“Deer regularly interact with humans and are commonly found in human environments – near our homes, pets, wastewater, and trash,” researcher and University of Missouri–Columbia professor Xiu-Feng “Henry” Wan, PhD, said in a statement. “The potential for SARS-CoV-2, or any zoonotic disease, to persist and evolve in wildlife populations can pose unique public health risks.”
In the Nature Communications paper, the researchers suggested that deer may be exposed to the virus from human food waste, masks, or other waste products. The authors concluded that further study is needed to determine how virus transmission occurs between deer and humans.
A version of this article first appeared on WebMD.com.