Hunting season fears: COVID

COLUMBUS, Ohio — Fall is fast-approaching and for many people that also means more contact with deer — especially if they’re hunters or live in rural areas. Now, concerning new research out of Ohio reports local deer all over the state are infected with SARS-CoV-2, the virus that causes COVID-19. While the prospect of disease-carrying deer is bad enough, researchers at The Ohio State University have also discovered that viral variants of SARS-CoV-2 mutate roughly three times faster in deer compared to humans.

With that in mind, the team at OSU call local deer “reservoirs” for the coronavirus promoting ongoing mutations. Researchers collected a total of 1,522 nasal swabs from free-ranging deer in 83 of the state’s 88 counties between November 2021 and March 2022 to facilitate these findings.

Over 10 percent of samples came back positive for the SARS-CoV-2 virus, and at least one positive case was documented across 59 percent of tested counties. Then, a genomic analysis revealed that at least 30 of those infections in deer had been introduced by contact with humans. Researchers were surprised by this discovery and are now concerned that COVID’s circulation among deer may eventually spread to other wildlife and livestock.

“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,” says Andrew Bowman, associate professor of veterinary preventive medicine at Ohio State and co-senior author of the study, in a university release.

“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.”

Prof. Bowman and the team previously reported detecting SARS-CoV-2 infections among local white-tailed deer across nine Ohio locations back in 2021, and continue to monitor deer populations for infection by newer COVID-19 variants.

“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 adds. “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.”

Beyond just detecting active infections, researchers also uncovered that roughly 23.5 percent of deer in Ohio have already been infected with a form of the coronavirus at one time or another. This was accomplished by examining blood samples containing antibodies.

The 80 whole-genome sequences gathered from collected samples accounted for different groups of viral variants: the highly contagious Delta variant, seen as the predominant human strain in the United States in the early fall of 2021 that accounted for almost 90 percent of the sequences, and Alpha, the first variant of concern to be given a name that circulated in humans around the spring of 2021.

Researchers’ analysis showed that the genetic composition of Delta variants in deer matched dominant lineages seen in human patients at the same time. This points to instances of human to animal transmission, with deer-to-deer transmission following in clusters, in some cases spanning multiple counties.

“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,” Prof. Bowman notes. “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.”

Researchers note that COVID-19 vaccination will likely help people against severe disease if a spillover back to humans takes place. For example, an analysis of the effects of deer variants on Siberian hamsters (often used as an animal model for SARS-CoV-2 studies), revealed that vaccinated hamsters did not become as ill from infection as unvaccinated animals.

Still, the variants currently circulating in deer are expected to continue evolving. Further analysis of mutations found in the samples showed evidence of more rapid evolution among both the Alpha and Delta variants in deer compared to humans.

“Not only are deer getting infected with and maintaining SARS-CoV-2, but the rate of change is accelerated in deer – potentially away from what has infected humans,” Prof. Bowman comments.

How the virus is transmitted from humans to white-tailed deer is still very much a mystery. So far, and on a positive note, despite there being roughly 30 million free-ranging deer in the United States, no substantial outbreaks of deer-origin strains have been seen in humans.

Circulation of SARS-CoV-2 among animals, however, remains highly likely. Prof. Bowman says that about 70 percent of free-ranging deer in Ohio still have not been infected or exposed to the virus, “so that’s a large body of naive animals that the virus could spread through rather uninhibited.”

“Having that animal host in play creates things we need to watch out for,” the study author concludes. “If this trajectory continues for years and we have a virus that becomes deer-adapted, then does that become the pathway into other animal hosts, wildlife or domestic? We just don’t know.”

The study is published in the journal Nature Communications.

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