SARS-CoV-2, the virus causing Covid-19, was transmitted from humans to deer, mutated, and was potentially transmitted back to humans many times, according to a study by the US Department of Agriculture (USDA).
The study, published in the journal Nature Communications, showed that SARS-CoV-2 is likely to have spread widely within the US white-tailed deer population (Odocoileus virginianus).
It showed that in late 2021 and early 2022, “SARS-CoV-2 was transmitted from humans to white-tailed deer at least 106 times in the US, mutated, and then in three instances may have been transmitted back to humans,” the USDA’s Animal and Plant Health Inspection Service (APHIS) said in a statement.
“This research is helping us understand if cervids, such as white-tailed deer, are acting as a host or “reservoir species,” meaning an animal host where the virus can survive and potentially change,” it added.
While experts are still learning about SARS-CoV-2 in animals, there is no evidence that animals play a significant role in spreading the virus to humans. “Deer regularly interact with humans and are commonly found in human environments — near our homes, pets, wastewater and trash,” Xiu-Feng Wan, an expert on zoonotic disease at the University of Missouri and an author of the new paper, said in a statement.
“The potential for SARS-CoV-2, or any zoonotic disease, to persist and evolve in wildlife populations can pose unique public health risks,” Wan added.
For the study, researchers collected 8,830 respiratory samples from free-ranging white-tailed deer across Washington, DC and 26 states in the US between November 2021 and April 2022.
They obtained 391 sequences and identified 34 Pango lineages including the Alpha, Gamma, Delta, and Omicron variants.
However, these lineages were identified in the deers at the time when only Delta and Omicron predominantly circulated in the human population. This indicates that the SARS-CoV-2 lineages were still present in white-tailed deer, months after the decline of those lineages in the human population.
Further, 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, the researchers said.
Viruses repeatedly adapted to white-tailed deer with recurring amino acid substitutions across spike and other proteins. “Our findings suggest that multiple SARS-CoV-2 lineages were introduced, became enzootic, and co-circulated in white-tailed deer,” the researchers wrote in the paper.
2023071237879
