Ames Plantation, in the middle of the CWD infection zone.
By Dr. Allan Houston
Chronic Wasting Disease was discovered in southwestern Tennessee in 2019. Certainly, the disease had been present on the local landscape for a number of years before it was discovered. It has since spread across much of western Tennessee.
Unfortunately, Ames Plantation in Grand Junction, Tenn. is in the middle of the infection zone; and compared to a decade ago, we are observing what might be typified as a younger and smaller herd.
CWD was first described in the mid-1960’s when penned deer in Colorado began to exhibit symptoms that were labeled as a mysterious “wasting syndrome.” Stress was usually blamed; but, in actuality no one knew the cause. In the late 1970’s, Dr. Beth Williams, a wildlife veterinarian, performed necropsies on deer and discovered brain lesions consistent with transmissible spongiform encephalopathy, which is a medically correct way of saying: an infectious disease that ends with a brain riddled with small holes.
A year later, a neurologist, Stanley Pruisner, discovered a very small protein that could become misshapen and influence other proteins to assume that same shape. These proteins, which he called prions, would proliferate inside the body, move into lymph systems and from there the nervous system and finally the brain, where they would clump and cause small holes, or as Williams noted, TSE.
CWD is confined to Cervids, or deer-like animals, including white-tails, mule deer, elk and moose. It is always fatal, usually killing a deer within 18-to-36 months. The prion is not alive; and with no genetic material, there is nothing to “kill.” Denaturing the prion requires 1,800 degrees F or highly concentrated chlorine solutions. The prion can be deposited onto the landscape with feces or urine, remaining durable and deadly for decades.
The prion is a multiforked dagger: deer are highly social and the prion can be transmitted as they lick and groom one another; prions are continually deposited on the landscape, nigh on to being indestructible, perhaps best imagined as a long-lasting poison; CWD can even arrive in newborn fawns with fetal transmission from the mother, although perhaps a moot factor with any infected mother apt to transmit the disease to a fawn anyway; deer live long enough to breed for a season or two and there is no strong genetic selection process to favor resistance; and bucks have a list of behaviors, especially during the breeding season, making them especially prone to exposure.
In the final stages, a deer is truly pitiable. It becomes emaciated, drooling, maybe propped against something or spraddled like a sawhorse, oblivious and aimless. The popular media, quick to coin a headline, labelled these “Zombie Deer;” and it quickly took root in the public consciousness this was a litmus for the prion’s presence in a herd – “See no Zombies, See no Disease.”
However, even with a high incidence of the disease, a deer in these final stages is essentially never seen. In the wild, as the disease progresses and before its ravages are apparent to a casual observer, deer become predisposed and succumb to other problems. They rarely live long enough to become zombies.
At Ames, every harvested deer arrives at the Check-In Station to be weighed and aged. Every deer is checked for CWD. It is extraordinarily rare for a deer to show symptoms obvious enough to say, “this one has CWD.” Yet, about a third of the does and half the bucks do have it.
Upon discovery in 2019, Ames began to move away from its highly successful QDM program and more toward CWD mitigation and an aggressive research program. Although the disease has been studied for more than half a century, there is much yet to learn, with every new piece of the puzzle helping in the fight and buying time as laboratories continue to seek ways to combat the prion.
We have developed research partnerships from around the country and these include TWRA’s help and involvement at every step. Colorado State University is testing dog’s ability to detect metabolites associated with the disease and have used Ames as a training ground. Work is ongoing with the University of Wisconsin to examine the presence of prions in mineral stations and how to go about neutralizing infected sites. Mississippi State University identified 105 scrapes on Ames and monitored these with cameras during the 2021-22 deer season, identifying 218 unique bucks, over 3,000 scrape interactions and more than 6,800 connections between bucks as they roamed across the 10,000-acre study area. Prions were found in some scrapes and also on the licking branches above the scrapes. These findings demonstrate the potential for scrapes to act as sentinels, a deer-installed system to detect CWD and act as an early warning.
A current study out the University of Tennessee is looking at both CWD and COVID in the Ames herd. Deer are captured, samples obtained, and fitted with collars reporting location every 30 minutes and able to send a “death signal.” The collars record proximity to other collared deer and there are stations scattered around Ames that turn on cameras when a collar is within a detectable radius to record interactions with uncollared deer.
Deer are one of the few animals, other than humans, that can contract COVID. As with us, the disease can have harmful lung effects; but the major concern is potential for a herd to harbor the virus and with continual mutation and transmission, eventually have a dangerous variant spill over into human populations.
The deer are captured with long hours, drop nets, cage-traps made of flexible nylon and dart guns with darts equipped with homing devices to help locate the animal.
A question regarding CWD: “is the meat safe to eat?” While there has never been a documented case of human illness with exposure to CWD, the potential for prion mutation and length of incubation are unknown. The CDC’s recommendation is to avoid meat from an infected animal because, “while the CWD threat to humans is low, it is not zero.”
In a final analysis, no one wants a fatal disease named after them.