Recent research led by the US Department of Agriculture’s Animal and Plant Health Inspection Service revealed that humans transmitted the coronavirus to white-tailed deer more than 100 times in late 2021 and early 2022.
The research suggests that the virus probably spread widely among deer, that it mutated in the animals, and that they may have passed these altered versions of the virus back to people at least three times.
The findings add to concerns that deer, which are very common in the US, might become a long-term animal reservoir for the virus and a potential source of new variants, reports The New York Times.
“Deer regularly interact with humans and are commonly found in human environments – near our homes, pets, wastewater and trash,” said Xiu-Feng Wan, an expert on zoonotic disease at the University of Missouri and an author of the paper, which was published in Nature Communications.
“The potential for SARS-CoV-2, or any zoonotic disease, to persist and evolve in wildlife populations can pose unique public health risks.”
There is no evidence that deer play a major role in spreading the virus to humans, but the transmission of the virus from people to animals raises several public health concerns.
First, an animal reservoir could allow viral variants that have disappeared from human populations to persist. In fact, the new study confirms prior reports that some coronavirus variants, including Alpha and Gamma, continued to circulate in deer even after they became rare in people.
New animal hosts also give the virus new opportunities to mutate and evolve, potentially giving rise to new variants that could infect people. If these variants are different enough from those that have previously circulated in humans, they could evade some of the immune system’s defences.
Background
Researchers at 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, the scientists ultimately collected more than 11 000 samples from deer in 26 states and the Washington district. Nearly a third of the animals had antibodies to the coronavirus, suggesting they had previously been exposed, and 12% were actively infected, APHIS said.
For the new Nature Communications paper, scientists from APHIS, the US Centres 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 they compared the viral 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 adapting 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.
Surveillance will continue
APHIS has expanded its surveillance to additional states and species.
Many questions remain, including precisely how people are passing the virus to deer, and the role that the animals might play in sustaining the virus in the wild.
Study details
Transmission of SARS-CoV-2 in free-ranging white-tailed deer in the United States
Aijing Feng, Sarah Bevins, Xiu-Feng Wan et al.
Published in Nature Communications on 10 July 2023
Abstract
SARS-CoV-2 is a zoonotic virus with documented bi-directional transmission between people and animals. Transmission of SARS-CoV-2 from humans to free-ranging white-tailed deer (Odocoileus virginianus) poses a unique public health risk due to the potential for reservoir establishment where variants may persist and evolve. We collected 8,830 respiratory samples from free-ranging white-tailed deer across Washington, DC and 26 states in the United States between November 2021 and April 2022. We obtained 391 sequences and identified 34 Pango lineages including the Alpha, Gamma, Delta, and Omicron variants. Evolutionary analyses showed these white-tailed deer viruses originated from at least 109 independent spillovers from humans, which resulted in 39 cases of subsequent local deer-to-deer transmission and three cases of potential spillover from white-tailed deer back to humans. Viruses repeatedly adapted to white-tailed deer with recurring amino acid substitutions across spike and other proteins. Overall, our findings suggest that multiple SARS-CoV-2 lineages were introduced, became enzootic, and co-circulated in white-tailed deer.
See more from MedicalBrief archives:
Next coronavirus variant could cause more illness, SA study finds
Virus hunters of Sierra Leone pursue the next deadly coronavirus
Will bird flu spark the next pandemic?
Global research group focuses on bats to avoid next pandemic