Nick Wilson/Daily Mining Gazette A male white-tailed deer in Keweenaw County.

HOUGHTON — A study from the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (USDA-APHIS) discovered that white-tailed deer populations in four states, including Michigan, carry antibodies against SARS-CoV-2, the coronavirus that causes COVID-19 in people.

This study indicates that deer have been exposed to SARS-CoV-2, and suggest that the virus has likely been circulating within the deer population. Researchers do not know how deer were first exposed to the virus.

The study analyzed 481 serum samples collected from free-ranging deer populations in Michigan, Illinois, Pennsylvania, and New York between January 2020 and March 2021. Researchers discovered antibodies in 33% of samples, although these results do not necessarily represent the prevalence of SARS-CoV-2 antibodies in the deer population as a whole.

In Michigan, 67% of the 113 samples contained antibodies. Michigan samples were collected in Emmett, Lenawee, Montmorency, Jackson, Presque Isle, Alpena, Alcona, Mecosta, Gratiot, Ingham, and Isabella counties. No UP counties were surveyed.

This study looked for antibodies in the animals’ blood, indicating some prior exposure to SARS-CoV-2, but not necessarily a current infection. More recently, deer sampled in Ohio tested positive for the virus itself.

Another study performed by researchers at Pennsylvania State University found active SARS-CoV-2 infections in Iowa’s deer population. This research, which has yet to be peer reviewed, analyzed samples from the lymph nodes of almost 300 wild and captive deer during 2020, and found that 30% carried the virus.

During the winter months of the study, when people experienced a surge in COVID-19 cases, researchers found that the rate of positive tests among deer climbed to 80%, making the prevalence of the virus in these deer 50 to 100 times higher than that of Iowa residents. Researchers also sequenced the genes of almost 100 samples of the virus, and found that the variants found in deer matched those circulating in people.

Although the virus does not seem to make deer sick, the presence of coronavirus in US deer herds could complicate the nation’s long-term COVID-19 recovery.

Researchers are concerned that deer could act as a “reservoir” for the virus, carrying it indefinitely and transmitting it back to humans. Another concern is the possibility of the virus mutating into a more virulent, more transmissible, or a vaccine-resistant strain within the deer population.

There are an estimated 30 million white-tailed deer in the US, including more than 1.5 million in Michigan, occupying a variety of habitat types and frequently coming into contact with people and domesticated animals.

However, scientists do not yet know whether deer can transmit the virus to people.

In an email to the Gazette, USDA-APHIS Legislative and Public Affairs Specialist Gail Keirn addressed some of the questions surrounding the recent studies, saying “Currently, there is no evidence that animals play a significant role in spreading SARS-CoV-2, the virus that causes COVID-19, to people. The risk of animals, including deer, spreading COVID-19 to people is low.”

Keirn also said that there is no current evidence that people can contract the virus from eating game meat. But because many other diseases can be transmitted to people when handling or eating game animals, Keirn encouraged hunters to observe good hygiene and follow safety precautions.

Michigan DNR Deputy Public Information Officer John Pepin also told the Mining Gazette that the DNR encourages people to adhere to safe practices for handling and cooking wild game as recommended by the Centers for Disease Control and Prevention (CDC). Pepin said that the Michigan DNR has not done any studies on COVID in deer.

While the question of deer to human virus transmission remains uncertain, previous studies have demonstrated that SARS-CoV-2 can be transmitted between humans and other species including domestic animals like cats and dogs, and zoo animals such as lions, jaguars, and multiple primate species.

Last year in Denmark, farmed mink contracted the coronavirus from humans, and then transmitted it back to people. The virus mutated inside of the mink population, although the mutated variants were not especially deadly. In response to these discoveries, Denmark slaughtered its entire population of 17 million farmed mink.

Additional research on U.S. deer populations is needed to determine how and where deer are exposed to the virus, whether new virus variants are emerging in deer, whether deer can transmit the virus to humans or other species, and what impact this may have on the trajectory of pandemic recovery.

Keirn’s statement also detailed plans for further research:

“APHIS and its state partners will begin a phased, multi-year approach this winter to understand the impacts of SARS-CoV-2 in deer to human and animal health. The goals are to determine how widespread the virus is in white-tailed deer populations in the United States and if deer can serve as a reservoir for the virus, potentially leading to new virus variants that may impact the health of deer, other animals, and people.”