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Deer Population Could Decline From Chronic Wasting Disease

One topic of concern is chronic wasting disease and its slow spread throughout the US and Canada. Now found in 30 states! Chronic wasting disease (CWD) is a prion disease that has no cure and is always fatal. It is similar to mad cow disease, but this fatal neurological disease occurs in cervids, such as deer, elk, and moose.

Recently, The Atlantic had an article about the spread of chronic wasting disease, and how it could ultimately result in the extinction of deer in the US. Some estimates already have the deer population down several million (for several reasons, not just CWD). Or perhaps deer populations will get decimated, with only some deer living and reproducing until the age of 2, and then dying.

This is because the disease can be transmitted before symptoms appear. It takes a while (more than a year) for a deer to show symptoms and die, and it can be passed to newborn fawns from the mother deer when she uses her tongue to groom the newborn.

Incredibly, the disease particles are shed into the environment (e.g., from deer feces) and stay in the soil for at least a decade. It can even be taken up by plants (thus it's in the leaves that deer eat) from the soil.

And yes, if you're wondering, scientists are very concerned that some day this incurable prion disease can make the jump to humans. So far it hasn't, but this is one reason why hunters are told to bring in deer heads for testing (and definitely to not eat deer meat until results come back negative).  Unfortunately, many people resist believing that there is a problem, and testing efforts vary from state to state.

Excerpts from The Atlantic: An Incurable Disease Is Coming for Deer

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.

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.”

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.

,,, 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.

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.

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