Mass. is monitoring white-tailed deer for COVID. Here's why
On a recent evening at the MassWildlife field headquarters in Westborough, Martin Feehan stood face-to-face with a 160-pound dead buck, splayed out on the loading dock.
The deer died of a broken leg, after it was apparently hit by a car in Needham. Feehan, a deer and moose biologist, had brought it to headquarters to test it for COVID.
He took a long white nasal swab out of its packaging, and stuck it up the deer’s nose.
“We go all the way in, and the idea is to saturate as much as the swab as possible,” he said, rotating the swab in tiny circles. “Just like every sampling that’s done for humans.”
Feehan pulled the swab out, covered in blood and mucus, and stored it in a vial.
This COVID test is bound for the U.S. Department of Agriculture’s National Wildlife Research Center in Colorado. Feehan will also send two samples of the deer’s blood to test for antibodies.
The SARS-CoV-2 virus has been found in white-tailed deer across the country, and Massachusetts is now one of 41 states participating in a national effort to study the prevalence of the virus in deer.
Scientists know that deer can be infected by the virus that causes COVID-19. Now they want to know how it happens, and whether the deer might spread it back to us.
“We do know that at this point, every place that [deer] have been tested, there have been antibodies found,” Feehan said. “Whether it’s transmitting amongst deer populations, whether they’re contracting it somewhere in the environment — or any other mode that they’re getting it — it is transmitting regularly to deer.”
The idea to test deer for COVID was set off after a 2020 study in the Proceedings of the National Academy of Sciences found that — theoretically — certain protein receptors in white-tailed deer, and a number of other animals, could make the animals vulnerable to infection by the novel coronavirus.
Scientists at the National Wildlife Research Center realized they could test the theory in real life, having banked deer blood for years.
They analyzed samples from Pennsylvania, New York, Illinois, and Michigan from 2021, and found COVID antibodies in 40% of them, indicating the deer had contracted the virus and recovered.
Furthermore, by comparing the 2021 blood samples to prior years, they found evidence of infection in deer only after the virus had first infected people, suggesting the deer somehow contracted it from us.
A later study out of Ohio State, published in Nature, found active infection in nearly 36% of the deer tested. That study also found that the prevailing variants in the deer matched the prevailing variants in the human population.
The authors say the evidence draws a clear line of transmission from people to deer.
“It was devastating to hear that these other species were getting infected with this new virus. It’s never something that you want to hear,” said Elinor Karlsson, director of the Vertebrate Genomics Group at the Broad Institute of MIT and Harvard.
Karlsson, who was involved in early work identifying white-tailed deer as potentially susceptible to the virus, said she was surprised to hear about the high percentage of infected deer.
“I certainly wouldn’t have expected to hear about that level, that number of individuals in a population having been exposed or being actively infected,” she said.
Jeremy Luban, a virologist at the University of Massachusetts Medical School who was not involved in the research, said he also found the findings stunning.
“The numbers in both of these studies are, I think most scientists would agree, are extraordinarily high,” he said.
Luban said we should be concerned about the virus jumping between species.
“So many of the viruses that we’re concerned about — the really serious viruses that cause serious human disease — have come to humans from other animals,” he said.
Scientists aren’t concerned that COVID will start killing off deer since the animals do not appear to develop severe symptoms. Rather, Luban said, scientists are concerned that deer could become a “reservoir” species, and that even as we get a handle on the pandemic, the virus could be spreading, replicating, and mutating alongside us, in our animal neighbors.
A new, more dangerous form of the virus could then “jump back” to us.
“If large numbers of deer are infected, that means the virus is spreading and replicating extensively among these animal populations. The virus then has more opportunity to mutate,” Luban said. “That, far and away, is the major concern.”
An example of this type of transmission and mutation played out recently with mink. Last year, mink at multiple fur farms in the Netherlands were diagnosed with the novel coronavirus. Workers at the farms then started getting sick.
A study later published in Science found the virus had spilled over from people to mink, mutated, and then spilled back to people in a slightly different form. The Dutch government has since culled hundreds of thousands of mink to prevent further infections.
Some scientists also suspect the highly-mutated omicron variant could have evolved in an animal before jumping back to people, in an example of “reverse zoonosis.” But the question is far from settled,
There’s no evidence of this type of transmission in the U.S. with deer, according to Luban, but we should keep monitoring how the virus spreads.
“It has potential to turn into something of great significance to all of us,” he said. “Once the cat’s out of the bag, there’s not that much we can do to control it.”
Once tested, the deer was placed in the game freezer for the night, nestled next to other important specimens, like moose heads to be tested for brainworm, and federally protected bald eagles.
“Most of our samples end up in the freezer, where we store some of them for like, decades,” he said.
While those species are not being tested for COVID right now, another iconic Massachusetts animal soon will be. Feehan said state wildlife managers will soon start testing hibernating black bears in their dens.
Results of the national study on deer are expected in the next few months. But that won’t be the buck’s only contribution to science.
Feehan has since removed its head and cleaned it with his wife over the holiday break. He said he’s planning to use the skull and antlers to teach schoolchildren about local wildlife.
Because, as the spread of the virus between us and deer shows, our lives and theirs are much more intertwined than we realize.