CWD Research, Insights Shared At Recent Deer Research Meeting
SAN ANTONIO — Gino D’Angelo, associate professor of deer ecology and management, University of Georgia, told those attending the recent Caesar Kleberg Wildlife Research Institutes (CKWRI) Deer Associates annual gathering that Chronic Wasting Disease (CWD) is the “greatest threat” to whitetail deer, and it’s a threat that is here to stay.
“In my estimation, all deer populations are going to experience the disease at some point,” D’Angelo told the group. “We’ll be dealing with this the rest of our lives.”
CWD is a transmissible spongiform encephalopathy caused by the abnormal folding of proteins, known as prions, which erode the brain, ultimately resulting in death. The disease may be spread by feces, urine, saliva, semen and the like when deer interact with each other. Also, the prions are persistent in the environment, held in the soil, and may be taken up by plants, at least experimentally.
“It's unlikely we're going to be able to scrub the wild environments of these prions,” D’Angelo told the group.
He also noted that bucks are more susceptible and are more likely to be carriers of the disease. Additionally, animals can be infectious and carry the disease for years before displaying clinical signs.
“That’s a concern and a challenge for management agencies,” he said.
Finally, he reiterated that the disease is always fatal for deer.
D’Angelo’s presentation focused on a large-scale whitetail deer research study conducted in Arkansas, in which he essentially witnessed firsthand “a train wreck,” a population decline caused by CWD.
The project objectives were to look at the abundance of deer, survival, recruitment and reproduction and the level of CWD infection by age and sex.
“Ultimately, we wanted to produce a tool for the state wildlife agency to understand how populations in the system would change over time relative to CWD and management,” said D’Angelo.
Additionally, researchers wanted to know if changing the season length and bag limits would lessen the impacts of CWD in this system. They also wanted to understand the impacts of this disease on the people living here. As D’Angelo explained, the people tend to be land rich and money poor, venison is an important component of their diets, and hunting is a cultural resource passed across generations.
The first incidence of CWD here was detected in the elk population, which cohabitates with the deer.
The research was conducted on state and federal lands in the Ozarks in the northwestern part of the state, where the disease is endemic, though researchers do not know where the disease originated. The terrain is rocky, and soils are thin and not highly productive. Much of it is a
closed canopy forest of primarily oaks. Consequently, acorns make up a large portion of the deer’s diet. The acorn mast goes through boom-and-bust cycles, and the deer population fluctuates accordingly through these boom-and-bust cycles. The deer battle the familiar predators, coyotes, black bear and bobcats.
There were three study areas: the Erbie Wildlife Management Area (WMA), the epicenter of CWD and where it was first discovered, the Gene Rush WMA and National Park Service land at Tyler Bend. Researchers surmised that disease prevalence would move from the epicenter at the Erbie WMA west to east.
Several hundred deer were under study using three camera grids of 81 cameras in each of the study areas, resulting in some seven million-plus photos. Researchers attempted to get the same deer sampled multiple times during the study.
Biopsy was used to detect the presence of prions. That entails collecting live animal tissue, specifically recto-anal mucosal-associated
lymphoid tissue or tonsils. If an animal died during the study, the obex was collected to determine whether it had CWD.
Essentially, what they found was consistent with other studies in that animals that were positive for CWD had a shorter lifespan. In fact, about 33 percent of the deer that became infected with CWD in their sample set died from CWD. The Erbie WMA, the endemic area, had the highest
prevalence rate at 50 percent. The other two areas had a prevalence rate in the 30s.
“We thought the prevalence rate for the two more eastern study areas would be perhaps five to 10 percent,” said D’Angelo. “Turns out the disease was well advanced even at the start of our study.”
The annual infection rate was about seven percent. That meant by 3.5 years of age, 50 percent were positive for CWD.
“We had deer dying at 3.5 to 4.5 years of age because of CWD, which led to fewer recreational opportunities from hunting,” said D’Angelo.
CWD prevents deer from behaving normally. For example, researchers found dead deer stuck in fences that were CWD positive. They simply didn’t have the capability to do what healthy deer normally can do, said D’Angelo. Another died after trying to swim a river, again something that a healthy deer would not have had an issue with, he noted.
They also saw quite a lot of predation of CWD-positive deer. He told the group that the CWD-positive deer that were predated by a coyote, for example, went into the killed by predation category, not the overall death by CWD category. The point being that the 33 percent “death by CWD” category was very conservative, said D’Angelo.
The researcher also told participants that CWD was found in tandem with Epizootic Hemorrhagic Disease (EHD) and other illnesses such as bacterial pneumonia.
The captured does were not only outfitted with a GPS collar but also a vaginal implant transmitter. That enabled researchers to also get collars on fawns and track their survival. The one bright spot was that fawn survival was relatively typical for a mountain environment at about 30 to 40 percent, D’Angelo told participants. Additionally, there was no statistical difference in fawn survival between does that had CWD and those that didn't.
“There is some vertical transmission between mom and fawn, but it's not always the case that a CWD-positive mother is going to have CWD positive
fawns,” D’Angelo stressed.
Looking at the CWD incident rate based on sex and age, he reiterated that males tended to have a higher likelihood of being positive. He attributed it to social interaction and their movement tendencies. Also, does at 4.5 years of age and older had a high infection rate.
He pointed out that in Wisconsin, where CWD was first discovered in the eastern U.S., the statewide prevalence rate is currently 11 percent.
“These rates in Arkansas are really concerning,” said D’Angelo.
Deer density estimates were not available before the study. Thus, they simulated density numbers for the life of the study. What they found was a 17 percent annual decline in deer density.
“We saw populations that were plummeting,” D’Angelo reiterated.
In the Erbie WMA, deer density was less than 2.5 deer per square mile, and deer were still being harvested here.
“That’s not a sustainable resource,” he stressed.
He next shared some of their genetically related findings. Specifically, there were some deer, “a couple dozen” in the study, that never became CWD positive. Of those, 6.5 percent were does and a few adult bucks. All were culled at the end of the study and found to be CWD negative.
“Maybe there's some hope there,” said D’Angelo.
He and his team are now under contract with the USDA to look further into the genetics piece of the equation in hopes of being able to identify gene-resistant CWD deer.
Summarizing the results, D’Angelo reiterated that animals are clearly dying here because of CWD. Luckily, fawn survival has been relatively stable. Finally, CWD prevalence is high and the population is declining. In the core endemic area, researchers recommended that the state suspend the harvest of female deer and consider suspending the harvest of males.
“That's how critical we believe it is,” said D’Angelo.
He then offered some additional comments about Wisconsin. CWD was discovered here in 2001. Yet, unlike the Arkansas study area, the deer population in Wisconsin is increasing and currently stands at about 1.8 million deer.
He described the farmland in southern Wisconsin as “a deer’s heaven,” abundant habitat, great food resources, including “beautiful” browse as well as ample cover. Many Boone and Crockett deer have been harvested in this region.
The state’s CWD prevalence rate is at 11 percent, though the highest prevalence rate is at about 20 percent. He also pointed out that the disease has not spread extensively to the big woods in northern Wisconsin. It is still mainly found in the most productive habitat in the state, the
farming area in the southern part of the state.
“We believe populations don’t decline in the face of CWD until they reach about 25 percent prevalence,” said D’Angelo. “That leaves us wondering if Wisconsin will stay below that level.”
He predicted that it may well be different in the state’s northern forest zone, where CWD is just starting to “trickle” in.
“We're talking about less animals and less quality habitats. That area could struggle with an additive issue of CWD.”
He then turned to a study done in North Georgia, though the study was not CWD-specific. It was chosen, in part, because the deer in this part of the state are in decline.
“Here in the Appalachians, we found that even when harvest of females is removed, the population still did not respond,” said D’Angelo. “It did not increase.”
He described it as poor habitat on public lands with little management. Namely, there has been little to no timber management.
Over the four years, the population continued to decline due primarily to poor fawn recruitment.
“We saw some of the highest fawn mortality rates in the country with only about 16 percent of the fawn surviving,” said D’Angelo.
Doe harvest has been removed, and yet populations have not responded.
“To increase fawn survival, we believe extensive habitat management must be done,” he told the group.
The National Deer Association has begun to work with the U.S. Forest Service to overcome some of the hurdles, namely the lack of management. However, D’Angelo opined that even with proper timber harvest over the next two decades, there will still not likely be enough early
successional plants for the deer to thrive here.
“My point is, we’ve got other deer herds across all Appalachians that are vulnerable, that are already in decline, or they're barely hanging on as stable. Put CWD on top of that, and that's going to be an issue,” he stressed.
He highlighted work from CKWRI in which researchers also found that in areas where the vegetation is poor, there are fewer deer and those deer tend to be in poorer condition.
He also pointed to CKWRI’s most recent Wildlife Monograph, in which the authors recommend that, in these fragile environments, managers should be cautious about including adult females in harvest prescriptions.
In closing, D’Angelo reiterated that in populations where CWD is prevalent, the deer are not going to live with the disease, they will die from the disease.
“It's not if, but when.”
Finally, he told the group that there is something for everyone to hate about CWD. He stressed the importance of effective communication and partnering in the deer community between researchers, managers, the hunting public and those indirectly tied to the hunting world.