New studies in the US demonstrate that SARS-CoV-2 - the virus that causes COVID-19 - was transmitted from humans to deer in dozens of cases.

It would then mutate and then in three instances the infection may have been transmitted back to humans.

Researchers say they are still trying to understand whether white-tailed deer are acting as a host or "reservoir species", meaning an animal host in which the virus can survive and potentially change.

While experts are still learning about SARS-CoV-2 in animals, there is no evidence that animals play a significant role in spreading the virus to humans.

The research, which involved sampling more than 11,000 white-tailed deer in 27 states, was carried out by the US Department of Agriculture's Animal and Plant Health Inspection Service (APHIS).

The service's acting administrator, Dr Mike Watson, said the studies were part of the effort to answer "critical animal and public health questions" around COVID-19.

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He added: "However, additional research using a one health approach is needed to understand what the risks are to wildlife conservation and public health with continued circulation of this disease in wildlife."

During the first year of sampling, APHIS and partners detected the virus in 12.2% of white-tailed deer, and 31.6% had antibodies indicative of previous SARS-CoV-2 exposure.

"Deer regularly interact with humans and are commonly found in human environments - near our homes, pets, wastewater, and trash," said Dr Xiu-Feng "Henry" Wan, a professor at the University of Missouri.

"The potential for SARS-CoV-2, or any zoonotic disease, to persist and evolve in wildlife populations can pose unique public health risks."