After Humans Spread COVID to Deer, They Got Us Back

Humans spread COVID-19 to American deer more than 100 times, according to a new analysis, which shows the "deer-adapted" virus jumped back to humans on a few occasions. The study, confirming early alpha and gamma variants were circulating in deer after becoming rare in people, raises concerns that the animals could maintain the virus, allowing it to mutate, before potentially passing new variants to people. "The potential for SARS-CoV-2, or any zoonotic disease, to persist and evolve in wildlife populations can pose unique public health risks," says study author Xiu-Feng Wan of the University of Missouri. He notes "deer regularly interact with humans and are commonly found in human environments—near our homes, pets, wastewater, and trash."

Scientists from the USDA's Animal and Plant Health Inspection Service initially collected more than 11,000 samples from wild white-tailed deer in 26 states and Washington, DC. Nearly a third had coronavirus antibodies, while 12% had active infections, per the New York Times. APHIS then joined with the CDC and the University of Missouri to sequence nearly 400 samples collected between November 2021 and April 2022, identifying variants including alpha, gamma, delta, and omicron. By comparing the sequences to publicly reported samples of human infections, they were able to trace the likely spread of the variants, per CBS News.

They concluded the virus had spread from humans to deer at least 109 times in "independent spillover events," according to the research published Monday in Nature Communications. The virus then spread from deer to deer at least 39 times, per the Hill. And it appears to have jumped back to humans at least three times. Two samples in North Carolina and one in Massachusetts carried mutations indicating the virus had moved from a human to deer, then back to humans. Researchers tracked down the three people with the "deer-adapted" mutation—which was also found among zoo lions—but all said they hadn't had close contact with deer or the zoo, per CBS. APHIS continues to look for the virus in additional species and states. (More COVID-19 stories.)