CHICAGO — The US government said on Friday it had confirmed the world's first cases of COVID-19 in deer, expanding the list of animals known to have tested positive for the disease.

The US Department of Agriculture reported infections of SARS-CoV-2, the virus that causes COVID-19, in wild white-tailed deer in the state of Ohio, according to a statement. There were no reports of deer showing symptoms of infection, the USDA said.

"We do not know how the deer were exposed to SARS-CoV-2," USDA spokeswoman Lyndsay Cole wrote in an e-mail to Reuters. "It’s possible they were exposed through people, the environment, other deer, or another animal species."

The USDA has previously reported COVID-19 in animals including dogs, cats, tigers, lions, snow leopards, otters, gorillas and minks.

Worldwide, most animal infections were reported in species that had close contact with a person with COVID-19, according to the agency.

The USDA reported last month that white-tailed deer populations in Illinois, Michigan, New York, and Pennsylvania were exposed to SARS-CoV-2, based on a study that analyzed serum samples from free-ranging deer for antibodies to the disease. — Agencies