A white-tailed deer at the Penn State Deer Research Center in State College, Feb. 2, 2022.  (Hannah Yoon/The New York Times)

A white-tailed deer at the Penn State Deer Research Center in State College, Feb. 2, 2022. (Hannah Yoon/The New York Times)

Even after the alpha and gamma variants of the coronavirus stopped spreading widely among humans, they continued to spread and evolve in white-tailed deer, according to a new study.

It is unknown if the variables are still circulating in the deer. “That’s a big question,” said Dr. Diego Dill, a virus expert at Cornell University and author of the study, published Tuesday in the Proceedings of the National Academy of Sciences.

But in the year The findings, based on samples collected through December 2021, provide further evidence that deer may be a reservoir of the virus and a source of future variants.

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“It’s a very large wildlife population in North America that has a constant and very intense relationship with people,” Dill said.

Previous studies on deer have shown that humans have frequently introduced the coronavirus into white-tailed deer in the United States and Canada, suggesting that deer can transmit the virus to one another. Scientists aren’t sure how humans transmit the virus to deer, but they speculate that it could happen when humans come into contact with human waste or waste from deer or reindeer.

The extent of the risk to humans from infected deer is not yet known. Scientists have reported a possible case of deer-to-human transmission in Ontario and noted that hunters and other people who have regular contact with the animals can contract the virus.

For the new study, Dill and his colleagues analyzed about 5,500 tissue samples collected from deer killed by hunters in New York state between September and December 2020 and 2021.

In the 2020 season, only 0.6 percent of the samples were positive for the virus, a figure that rose to 21 percent in the 2021 season.

Genetic sequencing showed that three types of concern — alpha, gamma and delta — were all present in deer during the 2021 season.

At the time, Delta was still prevalent among the human inhabitants of New York. But alpha and gamma have virtually disappeared, especially in rural parts of the state where infected deer have been found.

The scientists also compared the genomic sequence of the virus samples they found in the deer with those collected from humans. In deer, all three variants had new mutations that set them apart from the human sequence. But the researchers found that the alpha and gamma samples from the deer were significantly different from the human sequences than the delta samples.

Together, the results suggest that alpha and gamma have been circulating among deer and accumulating new mutations for months after spilling over into the human population, experts say.

Dr. Suresh Kuchipudi, a veterinary microbiologist at Pennsylvania State University, who was not involved in the new study, “supports the argument that deer can maintain lineages or diversity.”

The discovery not only raises concerns that deer could be a source of a new coronavirus that could be retransmitted to humans, but also raises the possibility that the virus could mutate in ways that pose a greater risk to wildlife, he said. “It can also be an animal health problem,” Kuchipudi said.

The study highlights the need for continued monitoring of wild deer populations, said Kuchipudi and D.L. DL and his colleagues are preparing to analyze deer samples during the 2022 hunting season to determine if the virus has spread among deer and which variants are circulating.

The Centers for Disease Control and Prevention recommends that deer hunters take several basic precautions to reduce their exposure to disease, including wearing a mask when handling game and washing hands thoroughly afterward.

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