The white-tailed deer – the most abundant large mammal in North America – harbors SARS-CoV-2 variants that were once widespread but are no longer present in humans.
studying, “white-tailed deer (Odocoileus virginianus) may serve as a wildlife reservoir for the nearly extinct SARS-CoV-2 variants of concern,” which was published January 31 in the journal Proceedings of the National Academy of Sciences, represents one of the most comprehensive studies to date to assess the prevalence, genetic diversity, and evolution of SARS-CoV-2 in white-tailed deer. The study focused on a group of white-tailed deer in New York.
“One of the most striking findings of this study was the discovery of the common distribution of three variables of concern — alpha, gamma, and delta — in these wild animals,” said Dr. Diego Delle, Associate Professor of Population Medicine and Diagnostic Sciences. and Director of the Virology Laboratory at the Animal Health Diagnostic Center at Cornell University College of Veterinary Medicine.
Although the exact cause is still unknown, research indicates that over the course of an epidemic, deer became infected with SARS-CoV-2 through constant contact with humans, possibly from hunting, rehabilitating wildlife, feeding wild animals, or through sewage or water sources.
This study was made possible by a program co-designed with Dr. Christine Schuller, assistant research professor of public and ecosystem health at CVM and lead author of the study. As director of the Wildlife Health Laboratory at Cornell, Schuler worked with the New York State Department of Conservation to design a statewide surveillance program for chronic wasting disease in white-tailed deer. The program collected thousands of samples of deer lymph tissue taken from deer killed by participating hunters.
“We were able to take advantage of those samples that were already collected and then tested for SARS-CoV-2, so we had good representation statewide,” Schuler said.
Testing detected potential infection hotspots across the state, including seven clusters where all samples from a specific geographic area contained the same variant. Samples from one group, for example, confined to one county, all tested positive for the gamma variant. Similar combinations of alpha and delta variants were found at different locations in the state.
When the researchers compared the genomic sequence of the variants found in the deer with sequences of the same variants taken from humans across New York, they found that the viruses had mutated in the deer, indicating that the variants had likely been circulating in the deer for several months. By the time alpha and gamma variants were discovered in deer, for example, there was no evidence that these viral strains were still circulating in humans. In fact, when it was found in deer, no variant was detected in humans in New York for four to six months.
In future work, Dale and colleagues hope to assess the effect of virus mutations, including whether these changes make the virus more or less able to bind to human receptors. Currently, only one study published in Canada has documented a human case of SARS-CoV-2 that originated in deer.
“Obviously, humans are still the primary reservoir and the possibility of anyone contracting SARS-CoV-2 is from another human, not a deer,” Schuller said.
More research is needed to confirm whether white-tailed deer did indeed become a reservoir for these now-extinct variants in humans or if the variants would disappear over time in the wild. Other questions include whether deer might spread SARS-CoV-2 to other wildlife animals, including predators.
Written by Krishna Ramanujan; the The full version of this story Appears in Cornell Chronicle.
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