Uh Oh, the Coronavirus Has Been Spreading Widely in U.S. Deer

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The coronavirus behind covid-19 appears to have found another species in which it can easily reproduce and spread. Preliminary research out this week seems to confirm that the virus is now freely circulating among wild deer. Though it’s unclear how important this discovery may be, it’s possible that it could affect our own future with covid-19.

Coronaviruses in general are known for their ability to infect a wide range of species — a trait that made them prime suspects for causing a pandemic, even before covid-19 arrived. And while the true origins of this pandemic are still being argued over, it’s clear that it didn’t take long for SARS-CoV-2 to make itself comfortable in other animals beside us. Cats, dogs, weasels, and even other primates like gorillas have all been documented carriers of the virus, along with deer.

In most of these reported animal outbreaks, humans have been implicated as the initial source of transmission. The virus has also been shown to be capable of spreading from animal to animal, particularly among weasels. These have often been isolated incidents, such as zoos where a worker might infect a few animals before the chain of transmission stops there. This new research, released as a preprint paper on Biorxiv, suggests that the virus has truly spilled over into at least some populations of white-tailed deer in the U.S. and is now widely spreading among them.

Researchers at Penn State and elsewhere tested lymph node samples collected from nearly 300 captive and free-living deer living in Iowa, looking for the presence of coronavirus RNA. The samples came from an already-established surveillance program for chronic wasting disease, an emerging illness in deer that many states are tracking. Between September 2020 and January 2021, about a third of these samples tested positive for the virus.

What’s more, the samples from free-living deer were more likely to test positive for the virus than captive populations (including those living on preserves). And when the authors tried to map out the geographic distribution and genetic signature of these cases, they determined that the virus had jumped over from humans to deer multiple times during those months and that it was then spreading among free-living deer.

In August, scientists with the USDA released research suggesting that up to 40% of deer in Michigan, New York, Illinois, and Pennsylvania carried antibodies to the coronavirus. But the authors say theirs is the first to show that the virus is almost certainly circulating among wild white-tailed deer, the most abundant deer species in North America. And that could carry some serious ramifications for our journey with the coronavirus moving forward.

“Our results suggest that deer have the potential to emerge as a major reservoir host for SARS-CoV-2, a finding that has important implications for the virus genomic diversity and future trajectory of the pandemic,” the authors wrote.

As they explain in the paper, viruses that only have one major host are easier to track and predict on an evolutionary level. But a virus that jumps between multiple species can pick up a wider array of mutations as it adapts, some of which could make the virus more likely to evade a person’s existing immunity or more likely to cause serious illness. A more travelled SARS-CoV-2 also has opportunity to mingle with other coronavirus species, allowing for unlucky genetic jumbles to occur. We see this dynamic play out already with influenza, which mutates very quickly for a virus but also occasionally swaps genes with the influenza viruses common to birds and pigs. Sometimes, this mix can produce a pandemic strain of flu on top of the seasonal flu we deal with every year. The coronavirus could also mutate to become more dangerous to deer, though lab experiments have suggested that most infected deer do not become sick currently.

If nothing else, simply having another place to crash could allow the coronavirus to bide its time before coming back into our lives. As the researchers note, “animal reservoirs can provide a refuge outside of a largely immune/vaccinated human population and thus represents a looming threat of reemergence into humans.”

Of course, the pandemic is still in our present. Much of the world remains unvaccinated, and it may take years before the virus will run out of fresh human bodies to easily infect. And it’s not inevitable that a deervid-19 would return with a vengeance down the line to severely plague humanity again. The virus may not actually become endemic in deer as it will in humans, but the potential risks posed by another nearby animal host of the coronavirus are definitely worth keeping an eye on, the authors say.

“Given the social and economic importance of deer to the U.S. economy, even while experimental evidence suggest that SARS-CoV-2 infected deer remain largely asymptomatic, the clinical outcomes and health implications of SARS-CoV-2 infection in free-living deer are unknown and warrant further investigation,” they wrote.




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