An Incurable Disease Is Coming for Deer

It was already dark when my family and I climbed into the big white pickup truck with Marcelo Jorge. A drizzly May night in the Ozarks; everything seemed soggy and muted. Jorge was upbeat, though. It was the peak of fawning season, and so far this year, his team had captured and collared a dozen fawns. The more deer they could collar, the more data they could collect about a disease threatening deer and their relatives.

Jorge is leading a multiyear study at the University of Georgia on chronic wasting disease, an always-fatal neurological illness. Ubiquitous deer may be, but in CWD, they face a serious threat. From its first appearance in Colorado in the late 1960s, CWD has crawled steadily across the country. It is now found in more than 30 states and multiple Canadian provinces.

Deer are all over the United States, trampling suburban lawns, running across highways, nibbling at crops. But, though seemingly counterintuitive, American deer might be on the decline. The trend is uncertain, but an estimate from G. Kent Webb, a professor emeritus at San Jose State University, suggests that deer’s total population peaked around the turn of the millennium, at about 38 million; we’re now at perhaps 35 million after a recent rebound. Although the more common white-tailed deer has been resilient, habitat loss and climate change are especially taking their toll on mule deer out west, which have declined substantially since their mid-20th-century peak. And CWD may have the potential to spread to every state. Even as deer numbers remain large, their slow disappearance would be a chilling prospect. Few of us have contemplated what a world without deer would look like.

In Jorge’s truck, we went bumping along dark gravel roads that threaded the forest; upslope, downhill, near rushing creeks, and along the flanks of steep dolomite hills. Forest crowded the roads on both sides. Prescribed burns by the state’s wildlife agency, Jorge told us, helped support the local deer by encouraging low, bushy vegetation that makes good deer food. But CWD was likely pulling the numbers the other way. The disease wasn’t detected until 2016 in this part of Arkansas, but the state soon learned it had probably been in the area for decades and, in some parts of the state, was infecting more than one in five deer.

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CWD is caused by a misfolded protein called a prion, which deer transmit through direct contact or by shedding prions into the environment. Ingested or inhaled, the prions slowly eat away at the animal’s brain and spinal cord. A deer can take well more than a year to show symptoms, but at some point the disease will leave it confused and weak. The deer’s body wastes away, and eventually, it dies. There is no treatment. Most ominously of all, the prions can bind with soil, where they can remain viable for more than a decade, Jorge told me, and can even be taken up by plants, time bombs in the leaves waiting to infect more animals. Any member of the cervid family, which includes elk and moose, can be infected.

It’s the deer equivalent of mad-cow disease, and though it’s never been known to jump to a human, the possibility lurks like a black cloud in the back of many studies, articles, and public notices about CWD. COVID, ebola, swine flu—all sorts of recent pathogens are suspected to have come from animals. CWD “seems like a juggernaut of a disease,” Jorge said. “It’s a very insidious and scary thing.”

The Age Of Deer: Trouble And Kinship With Our Wild Neighbors

By Erika Howsare

As CWD has moved around the U.S., it has also brought human concern and confusion. Jorge and others have compared the situation to the coronavirus pandemic: Each state creates its own regulations, with piecemeal national policy, and much of the public is often skeptical. That regulatory patchwork is especially troubling when it allows deer to be shipped across state lines. A major vector for CWD is thought to be the transport of captive deer by the deer-farm industry, which breeds deer for venison and antlers, and as game animals. When captive deer are sold, they may get driven long distances, possibly carrying prions with them. One Wisconsin deer farm discovered an outbreak of CWD among its animals in 2021; reportedly, officials soon realized that over the previous five years, the farm had shipped nearly 400 potentially infected deer around Wisconsin and to six other states.

Because the disease can be transmitted by a positive animal long before it causes symptoms, it’s especially hard for wildlife agencies to get a handle on what’s happening with deer in a given area. “We can’t see them until it’s too late,” Jeannine Fleegle, a wildlife biologist at the Pennsylvania Game Commission, told me. “I wish the disease would evolve to make them sicker, faster.”

Deer are one of evolution’s best survivors, having come back in the 20th century from severe overhunting. But a mostly invisible, universally fatal disease that persists in the environment for years sounds like a recipe for disaster. I found myself asking Jorge a question that, despite having researched an entire book about deer, had never even crossed my mind before: Could CWD actually cause the extinction of deer? “I think it’s a possibility that is on the table,” he said. But he emphasized that extinction is only one of a spectrum of outcomes, and no one really knows what will happen.

One possibility: The many species of deer could limp along in a diminished fashion. Preventing transmission to future generations is nearly impossible; CWD might be passed from mother to fawn in the first couple of hours after birth, Jorge said, as the mother uses her tongue to groom her baby. That’s the same amount of time that he and his team try to give newborn fawns to adjust to life on Earth before they descend on them with collars. That night, I witnessed them catch and take samples from a fawn whose soft hooves suggested that she was only a few hours old. She might have already been carrying her very first few CWD prions, which could kill her by about the age of two. In that length of time, deer can reproduce—meaning that one possibility, Jorge said, “is that we will have a deer population, but they’ll all have CWD” and die by the age of two or three.

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Another possibility: In some areas, deer may begin to vanish. Such local declines might not seem dramatic, especially for an animal as globally abundant as deer, but they add up nonetheless. Small-scale dwindlings threaten all kinds of species across our warming planet. CWD is most prevalent in the upper Midwest, the Great Plains, and the mid-Atlantic; in places where other members of the deer family are also found, those animals are also at risk.

To ward off disaster, several states have tried culls to slow the spread. But many hunters oppose these actions, and they also show sometimes-spotty compliance with rules about transporting their kills and getting them tested. And deer farmers, like the members of any industry, can be skeptical of any new regulation on their work.

Jorge’s study will try to model the effects of different management actions, but there aren’t a lot of great options. CWD spreads in stealth, and it seems that all officials can do is try to slow it down. In some areas, more than half of adult bucks are likely already infected. States declare containment zones where they find infections, but without a clear picture of where the prions actually exist, these aren’t always effective.

Because CWD-infected animals look normal until the end stages of illness, Jorge said, the disease is difficult for people to believe in. Humans “are really bad at looking into the future. You see the deer now, and most of them look healthy. If we say, ‘They could go extinct,’ it’s hard to grasp.” He drew an analogy to climate change: It’s hard to fathom how large numbers of seemingly healthy animals could vanish, just as it was hard to imagine historic flooding and wildfires devastating many chunks of the country until it became the norm.

But in this part of Arkansas, Jorge told me, you can sometimes see CWD plainly. Near death, deer look and act weird. Their front legs splay out; they lose the alertness and wariness that is their very essence. “They’re very obvious,” he said. “We just drove by one last week—a deer hanging out on the side of the road.” He pulled off the highway. “I started walking toward it and it just kind of stared. It was very skinny. Cars were driving a foot away from it and it wasn’t even flinching.” Locals have told him similar stories.

Thirty-five million deer, of course, remains a lot of deer. Even if local declines lower their numbers by millions more, hunters and ecologists might at first be the only ones to notice. Yet whether we think of them or not, deer are part of everyone’s life; most of us see them at least occasionally, and they are icons in art, literature, and design. They are also key members of the ecosystems they inhabit and a flagship game animal in the $45 billion American hunting industry. A disease that could drastically change their presence in our world might be a quiet force. But it’s one we should consider deadly serious.

This article has been adapted from Erika Howsare’s forthcoming book, The Age of Deer: Trouble and Kinship With Our Wild Neighbors.