Deer may have transmitted SARS-CoV-2 back to humans, study finds
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Key takeaways:
- More than 100 SARS-CoV-2 infections among white-tailed deer originated from human spillover.
- This resulted in 39 cases of local deer-to-deer transmission and three potential cases of spillover back to humans.
Thousands of samples taken from white-tailed deer in the U.S. showed that SARS-CoV-2 was transmitted from humans to deer more than 100 times, mutated and then was potentially transmitted back to humans in three cases, researchers reported.
“These findings suggest that white-tailed deer could potentially serve as a reservoir for
SARS-CoV-2, presenting zoonotic risks to humans,” Aijing Feng, PhD, a postdoctoral fellow at the University of Missouri’s Center for Influenza and Emerging Infectious Diseases, and colleagues wrote in Nature Communications.
Additionally, they said that spillover back to humans of SARS-CoV-2 viruses that have mutated while circulating among deer “has the potential to undermine the effectiveness of the pre-existing immunity … generated from previous SARS-CoV-2 infections and/or vaccinations within the human population.”
It was not the first report of humans getting SARS-CoV-2 from deer. Feng and colleagues noted that previous evidence of transmission from white-tailed deer to people was reported in Canada.
“Since its emergence in 2019, SARS-CoV-2 has evolved rapidly and produced numerous SARS-CoV-2 genetic variants,” they wrote. “In addition to humans, SARS-CoV-2 infections have been documented in a wide range of wild, domestic, and exotic animals in captivity, such as deer, mink, rats, otters, ferrets, hamsters, gorillas, cats, dogs, lions, and tigers. Further, SARS-CoV-2 transmission from animals to humans, while not common, has been documented or suspected in farmed mink, domestic cats, and white-tailed deer, highlighting animals as potential reservoirs for secondary zoonotic infections.”
To assess potential transmission between humans and white-tailed deer, Feng and colleagues collected 8,830 respiratory samples from free-ranging white-tailed deer from 26 states and Washington, D.C., between Nov. 4, 2021, and April 4, 2022.
Testing of the samples found that 944 had detectable SARS-CoV-2. The study included 383 of these samples from 23 states with complete metadata, including 282 samples that were used to identify of 34 lineages of SARS-CoV-2 belonging to B.1 and the alpha, gamma, delta and omicron variants.
Of those 282 samples, 238 were grouped into 109 clusters that also contained human SARS-CoV-2 viruses, according to Feng and colleagues. For each cluster, the researchers identified a SARS-CoV-2 genomic sequence from a human as the “precursor virus,” indicating at least one independent spillover event from humans to white-tailed deer.
Further analyses showed that human-to-deer spillover events resulted in 39 cases of subsequent deer-to-deer transmission and three cases of potential spillover from white-tailed deer back to humans.
In a press release, the U.S. Animal and Plant Health Inspection Service (APHIS) said there is currently no evidence showing that animals play a significant role in spreading the SARS-CoV-2 to humans, and that efforts are ongoing to better understand SARS-CoV-2 in animals.
“APHIS’s work to answer critical animal and public health questions around SARS-CoV-2 is continued with this research,” Mike Watson, PhD, acting administrator of APHIS, said in the press release. “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.”
References:
APHIS releases research on SARS-CoV-2 transmission in white-tailed deer throughout U.S. https://www.aphis.usda.gov/aphis/newsroom/stakeholder-info/sa_by_date/sa-2023/white-tailed-deer-research-sars-cov-2. Published July 11, 2023. Accessed July 12, 2023.
Feng A, et al. Nat Commun. 2023;doi:10.1038/s41467-023-39782-x.
Perspective
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This is a comprehensive study that raises the alarm for the establishment of SARS-CoV-2 transmission cycles in wildlife in the U.S. — in this case, white-tailed deer. The public health implications of this remain complex, but spread in animals could create a scenario in which new and/or ancestral variants emerge that could undermine immunity in the human population. Continued wildlife surveillance, therefore, is paramount to better understand the evolving landscape of zoonotic SARS-CoV-2 in the U.S.
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