The evolution of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from humans to white-tailed deer, and its transmission ability in the deer population is the driving force behind the study conducted by the Cornell Veterinary Medicine (CVM).
The study, “White-tailed Deer (Odocoileus virginianus) May Serve as a Wildlife Reservoir for Nearly Extinct SARS-CoV-2 Variants of Concern,” published in the Proceedings of the National Academy of Sciences journal, looks into the role of the white-tailed deer in the epidemiology and ecology of the virus. The study focused on the deer population in New York.
“One of the most striking findings of this study was the detection of co-circulation of three variants of concern–alpha, gamma and delta–in this wild animal population,” says Diego Diel, DVM, MS, PhD, associate professor of population medicine and diagnostic sciences and director of the Virology Laboratory at the Cornell University CVM Animal Health Diagnostic Center.
While the exact cause remains unknown, research indicates that over the course of the pandemic, deer have become infected with SARS-CoV-2 through contact with humans, possibly from hunting, wildlife rehabilitations, feeding of wild animals or through wastewater or water sources.
This study was made possible through a program co-designed by Krysten Schuler, PhD, assistant research professor of public and ecosystem health at CVM and a senior author of the study. As director of the Cornell Wildlife Health Lab, Dr. Schuler has worked with the New York State Department of Environmental Conservation to design a statewide surveillance program for chronic wasting disease in white-tailed deer. The program collected thousands of samples of deer lymph tissues taken from deer killed by participating hunters.
“We were able to leverage those samples that had already been collected and then test them for SARS-CoV-2, so we had a good statewide representation,” says Schuler.
The testing revealed potential hotspots of infection across the state, including seven clusters where samples from a defined geographic area all contained the same variant. Samples from one cluster, for example, confined to one county, all tested positive for the gamma variant. Similar clusters were also found for alpha and delta variants in different locations in the state.
When researchers compared the genomic sequences of the variants found in deer with sequences of the same variants taken from humans across New York, they found the viruses had mutated in the deer, suggesting the variants had likely been circulating in deer for many months.
By the time alpha and gamma variants were detected in deer, for example, there was no evidence of these viral strains still circulating in humans. In fact, when they were found in deer, neither variant had been detected in humans in New York for four to six months.
In future work, Diel and colleagues hope to assess the effect of the viruses’ mutations, including whether these changes make the virus more or less capable of binding to human receptors. Currently, only one study published in Canada has documented a case of a human being infected by SARS-CoV-2 that originated in deer.
“Obviously, humans are still the primary reservoir and the likelihood of anybody getting SARS-CoV-2 is from another human rather than a deer,” Schuler said.
For more information on the research findings, click here.