COLUMBUS, Ohio — A new study reveals that a growing number of white-tail deer in Ohio have been infected with COVID-19, with variants of the virus evolving nearly three times faster than in humans.
In the study, published earlier this week by Nature Communications, scientists collected 1,522 nasal swabs from free-ranging deer in 83 of the state’s 88 counties between November 2021 and March 2022. From the samples, more than 10% were positive for COVID-19, and at least one positive case was found in 59% of the counties in which testing took place.
One statistic that surprised the research team, including Ohio State University associate professor of veterinary preventive medicine Andrew Bowman, was that at least 30 of the COVID infections in deer were introduced by humans.
“We generally talk about interspecies transmission as a rare event, but this wasn’t a huge sampling, and we’re able to document 30 spillovers. It seems to be moving between people and animals quite easily," Bowman, who was one of the study's co-senior authors, told Ohio State News. "And the evidence is growing that humans can get it from deer – which isn’t radically surprising. It’s probably not a one-way pipeline.”
The overall findings suggest that the white-tailed deer species is "a reservoir for SARS-CoV-2" that enables continuing mutation. The virus’s circulation in deer could lead to its spread to other wildlife and livestock.
In addition to active infections, researchers say they discovered antibodies in blood samples indicating that nearly 25% of deer in Ohio had been infected with the virus at some point.
Infections in white-tailed deer were first reported in nine parts of Ohio in December of 2021. Bowman said the study was then expanded to the state as a whole to determine whether it was a localized issue or one that was more widespread.
“We expanded across Ohio to see if this was a localized problem – and we find it in lots of places, so it’s not just a localized event,” Bowman added. “Some of the thought back then was that maybe it’s just in urban deer because they’re in closer contact with people. But in rural parts of the state, we’re finding plenty of positive deer.”
Two groups of viral variants were discovered in the samples: the delta variant, which was the predominant human strain in the U.S. in the early fall of 2021. There was also the alpha variant, which first circulated in the spring of 2021.
“There’s probably a timing component to what we found – we were near the end of a delta peak in humans, and then we see a lot of delta in deer,” Bowman stated. “But we were well past the last alpha detection in humans. So the idea that deer are holding onto lineages that have since gone extinct in humans is something we were worried about.”
The study also suggests that the COVID-19 vaccination is likely to help protect people against severe cases of the virus in the event of a spillover back to humans.
How the virus is transmitted from humans to white-tailed deer remains a mystery to researchers. Thus far, even with about 30 million free-ranging deer in the U.S., no substantial outbreaks of deer-origin strains have occurred in humans.