There is no evidence that deer play a major role in spreading the virus to humans, but the transmission of the virus from humans to animals raises several public health concerns.

First, an animal reservoir could allow viral variants that have disappeared from human populations to persist. Indeed, the new study confirms previous reports that some coronavirus variants, including Alpha and Gamma, continued to circulate in deer even after they became rare in humans.

New animal hosts also give the virus new opportunities to mutate and evolve, potentially giving rise to new variants that could infect humans. If these variants are sufficiently different from those that have previously circulated in humans, they could evade some of the immune system’s defenses.

Researchers from the Animal and Plant Health Inspection Service, in collaboration with other government and academic scientists, began looking for the coronavirus in free-ranging white-tailed deer in 2021, after studies suggested the animals were susceptible to the virus.

In that first year of surveillance work, the scientists finally collected more than 11,000 samples from deer in 26 states and Washington. Almost a third of the animals had antibodies to the coronavirus, suggesting they had been previously exposed, and 12 percent were active. infected, APHIS said Tuesday.

For the new Nature Communications paper, scientists from APHIS, the Centers for Disease Control and Prevention and the University of Missouri sequenced nearly 400 of the samples collected between November 2021 and April 2022. They found multiple versions of the virus in deer, including the Alpha. , Gamma, Delta and Omicron variants.

Then, the scientists compared the virus samples isolated from deer with those from human patients and mapped the evolutionary relationships between them. They concluded that the virus moved from humans to deer at least 109 times and that deer-to-deer transmission often followed.

The virus also showed signs of adaptation to deer, and the researchers identified several cases in North Carolina and Massachusetts in which humans were infected with these “deer-adapted” versions of the virus.

APHIS expanded its surveillance to additional states and species.

Many questions remain, including exactly how humans transmit the virus to deer, and the role the animals might play in perpetuating the virus in the wild.

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