LOS ANGELES - As the latest proof showed that white-tailed deer can contract and carry COVID-19, health experts in the United States said the situation is concerning.

Jennifer Ramsey, wildlife veterinarian for Montana Department of Fish, Wildlife and Parks (FWP), was quoted by the Billings Gazette newspaper Monday as saying that a recently released study, which found about one-third of 283 captive and free-ranging deer had tested positive for the infection, rose concerns about deer being a reservoir for the virus to mutate.

"There's a lot of uncertainty about how deer are getting exposed, and what this will mean for wildlife and humans over time," she said.

"What's the highlight of this research is that this is a free-ranging animal we don't have reason to suspect has any intimate human contact," Rachel Ruden, a coauthor of the paper and member of the Iowa State College of Veterinary Medicine, told the Duluth News Tribune. "But they're still getting this infection."

According to the paper published on biorxiv.org, an online preprint repository for the biological sciences, SARS-CoV-2 was detected in one-third of sampled white-tailed deer in Iowa between September 2020 and January of 2021 that "likely resulted from multiple human-to-deer spillover events and deer-to-deer transmission."

"The geographic distribution and nesting of clusters of deer and human lineages strongly suggest multiple zooanthroponotic spillover events and deer-to-deer transmission," the paper read. "The discovery of sylvatic and enzootic SARS-CoV-2 transmission in deer has important implications for the ecology and long-term persistence, as well as the potential for spillover to other animals and spillback into humans."

An estimated 30 million white-tailed deer live in the United States.

The Billings Gazette also reported that in early August the US Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) published information showing COVID-19 antibodies in 33 percent of 481 samples collected from deer in Illinois, Michigan, New York and Pennsylvania.

The presence of antibodies means the animals had been exposed to the virus but not necessarily infected. "We do not know how the deer were exposed to SARS-CoV-2," APHIS wrote in its report. "It's possible they were exposed through people, the environment, other deer, or another animal species."

Then in late August APHIS confirmed COVID-19 in wild whitetails in Ohio, which is the first deer confirmed with the SARS-CoV-2 virus worldwide.

However, APHIS, which also monitors diseases like brucellosis found in bison and elk in the Greater Yellowstone Ecosystem, said the risk of spreading disease from deer to people is low.