JUDY WOODRUFF: Scientists have recently discovered what they are calling a silent
outbreak of coronavirus among white-tailed deer.
William Brangham is back now with this report about how one of the most ubiquitous species
in North America got COVID and what that means for the future of the pandemic.
And a warning: Viewers may find some of the images in this report distressing.
WILLIAM BRANGHAM: They are an elegant sight dancing through the trees.
There are an estimated 25 million white-tailed deer in the U.S.,
and now scientists have learned some have shockingly high rates of COVID infections.
SURESH KUCHIPUDI, Virologist, Penn State University: The
level of infectivity we found in these animals was truly stunning.
VIVEK KAPUR, Infectious Disease Specialist, Penn State University: Gobsmacked is the word I used.
WILLIAM BRANGHAM: That's the technical term for it?
(LAUGHTER)
VIVEK KAPUR: That's the technical term, is gobsmacked. It was quite, quite striking.
So, these are the Penn State Deer facilities, the facilities...
WILLIAM BRANGHAM: Oh, I see where it gets its name, all the deer.
Stunning, gobsmacked, striking, not the usual vocabulary for scientists.
So, on a cold Pennsylvania day, I went out with veterinary virologists Suresh Kuchipudi and Vivek
Kapur to see some deer up close. This is an enclosed facility at Penn State University.
And the scientists said it's fine for us to be near them.
And some of the deer, like tiny Peanut, who was raised in captivity and bottle-fed by humans,
wanted to be near us. It was in Kapur and Kuchipudi's labs here at Penn State that
they made this remarkable discovery about widespread infections in deer.
And it raises concerns about whether humans can fully control this coronavirus.
SURESH KUCHIPUDI: This is the first time
a widespread natural infection of a wild animal species has been demonstrated, which
really changes the way we ought to understand this pandemic and the virus.
WILLIAM BRANGHAM: It began with these deer lymph nodes from Iowa collected
when deer were killed by hunters or cars at various times during the pandemic.
Researchers in Iowa weren't looking for COVID. They were tracking what's known
as chronic wasting disease. but Kapur and Kuchipudi took the samples and tested them
to see if deer had gotten COVID, and when.
VIVEK KAPUR: September, the first positive there. October, another one shows up. November.
WILLIAM BRANGHAM: Wow.
VIVEK KAPUR: And, December, all that positive.
WILLIAM BRANGHAM: Wow.
VIVEK KAPUR: You Zoom out into the state, the whole state. You can see this event in different
parts. With these samples, about 30 percent of them overall were positive at this stage.
SURESH KUCHIPUDI: If you look at the spread of these red dots on the map, these are all
individual clusters, which also points to the fact that there are multiple spillover events happened.
WILLIAM BRANGHAM: Spillover, meaning the virus that was circulating in humans
spills over into the wild animal population.
VIVEK KAPUR: So, out of just under 2,000 samples collected, 1,200 were positive.
It's just completely amazing. If this were happening in humans, you would just give up, yes.
(CROSSTALK)
VIVEK KAPUR: It's just incredible to see that to see how quickly this occurred.
WILLIAM BRANGHAM: And, of course, because there's no interventions,
they're not -- they don't know to distance or mask or no vaccines. And...
There's no evidence infected deer showed any symptoms of COVID-19.
The virus seems not to affect them. The Iowa samples showed they got the same variants
we got. And by tracking the timing of the infections, and using genomic sequencing,
the researchers are certain humans gave the virus to the deer, not the reverse.
But how?
With the exception of Peanut here, who does seem very eager to interact with humans,
most humans don't have interactions like this with the deer. So, how is it possible that that we gave
the virus to them?
SURESH KUCHIPUDI: It doesn't necessarily require a direct interaction between a human and the deer.
A kid throwing half-eaten apple or leftover food or somebody's feeding deer in their backyard,
all it takes is just one or two deer to pick up the infection.
They can transmit the virus among themselves very effectively. And once one animal gets infected,
the virus spreads among them very, very quickly.
VIVEK KAPUR: If you look back there, you can simply see them interacting...
WILLIAM BRANGHAM: Right. They're all...
VIVEK KAPUR: ... quite a lot. They're all huddled up.
WILLIAM BRANGHAM: They're all very packed together.
VIVEK KAPUR: Yes. They're all huddled up.
And then, if you have ever walked in a forest and seen deer, it's -- and they're blowing, you just
see plumes of their breath come out. And given what we know about the amount of virus that these
deer had, it's very easy to see why they were so susceptible and it spread explosively in herds.
WILLIAM BRANGHAM: Given what your findings in Iowa indicate, should we just make the assumption
that deer, white-tailed deer all over North America, are carrying the virus?
VIVEK KAPUR: I think it's safe to assume that that would be the case.
WILLIAM BRANGHAM: These human-to-animal leaps by the coronavirus aren't unheard of.
While this research is the first known case in a wild population,
there are examples with more domesticated animals. In the Netherlands, scientists discovered that,
when pet owners got COVID, their dogs and cats had a one-in-five chance of getting it too.
In Hong Kong, a pet store hamster got the virus,
and officials then killed 2,000 others to stop any further spread.
All this leads to a potentially more troubling issue. If humans can mutate
the virus and pass different variants to deer, could deer do the same in reverse, meaning,
could they create new variants and pass those back to us?
It's not impossible. In 2020, in Denmark, officials killed the country's entire
population of farmed mink after a mutated COVID strain jumped from mink back to humans.
But Kapur and Kuchipudi say, thus far, there's no evidence that's happening with deer.
SURESH KUCHIPUDI: This is still primarily a pandemic of a virus that is
spreading in human beings across the world. And, so far,
all the animal infections have been opportunistic spillover from human beings.
VIVEK KAPUR: My personal feeling is, actually,
deer are more likely to get the infection from humans than give it to humans.
And so I think we also have to be respectful that, when we are going out, we're likely to be
transmitting just as easily to deer, animals we love, than getting the infection back.
WILLIAM BRANGHAM: We're the problem here, for the most part, not them.
VIVEK KAPUR: We're the initial problem. And we want to make
sure that they don't become a problem for us in the future.
WILLIAM BRANGHAM: These scientists say that, given how widespread deer and this virus are
in North America today, much more research needs to be done about this potential threat.
For the "PBS NewsHour," I'm William Brangham in State College, Pennsylvania.