Photo by Garrett Mynatt
A frothy trail of saliva hangs to the ground as a mule deer slumps onto the bank of a river. The deer’s rough, patchy coat is stretched and looks melted on its rocky frame. Its eyes are bulging and transfixed on nothing. It is clear this animal is in pain. Its last moments are spent seeking an end to its perpetual thirst, but nothing can help the deer in its final stages of the always-fatal Chronic Wasting Disease.
This deer, like many of the cervid family (white tail and mule deer, elk and moose) in northern Larimer County are dying from this neurological disease.
And CWD is not letting up anytime soon.
“Prevalence rates aren’t going down, they’re going up – we don’t have a handle on it [CWD] yet,” said Kurt C. VerCauteren, a research wildlife biologist and CWD project leader at the National Wildlife Research Center, which is a part of the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service. He added that 40 percent of the deer in this area are infected with CWD.
Although humans cannot contract CWD, it is in the same family of diseases known as Transmissible Spongiform Encephalopathies, which includes mad cow disease, scrapie in sheep and goats and Creutzfeldt-Jakob Disease in humans.
There is no known cure or vaccine, and this disease is difficult to detect in wild and captive species because the signs don’t show up until the animal is in its final stages.
According to the APHIS Web site, the disease first appeared in Colorado wildlife research facilities in 1967. For years CWD stayed around northern Colorado and in parts of Wyoming. It wasn’t until 2001 that an infected mule deer was found in Nebraska. Since then, the disease has spread throughout many states, but the heavy concentrations are in Colorado, Wyoming, Nebraska, Wisconsin, Minnesota and two Canadian provinces, which includes both wild and captive cervids.
After CWD appeared in other states, researchers could not figure out how it spread or how this disease was transmitted, aside from saliva contact. Only now are researchers learning the ins and outs of CWD.
N. Thompson Hobbs, an ecology professor and senior research scientist at Colorado State University’s National Research Ecology Lab, said one of the ways CWD can be transmitted is by one sick animal to another, and his research shows how the disease can manifest itself in other ways, too.
“Chronic Wasting Disease can be transmitted from the environment probably from urine, feces and residues from carcasses,” Hobbs said. “It is persistent in the environment, which makes eradication of the disease a much more challenging problem.”
Hobbs is leading a research team that was given a $2.5 million grant from the National Science Foundation to conduct an observational study about how CWD is transmitted among wild mule deer populations. His team will look at the different conditions of hunted mule deer and different soil compositions, particularly clay soil. Hobbs said that in the laboratory, clay soil is shown to elevate “the ability of the disease to be transmitted from the environment,” which is what one of their several hypotheses is centered on.
“Animals that live in areas dominated by clay soils have a higher risk of infection,” Hobbs said. “Prions that adhere to particles of clay are shown to be 200 times more infectious than those that are not, so the environment plays an important role.”
The main soil in northern Colorado has a heavy concentration of clay. So what does that mean for the cervids in this area?
“They’re getting dosed, potentially, quite a bit,” VerCauteren explained. “CWD has been here for a long time and environmental contamination is a larger issue than we realized even just a couple years ago. So these environments are contaminated and the longer you have infected animals in the area, it keeps building.”
So whether an elk touches or sneezes on another elk, it isn’t the only way CWD is transmitted. If a plant grows from the soil with a heavy concentration of CWD (from urine, feces or carcass residue from an infected animal) then there is potential transmission.
Photo by Stephanie Scott
But if soil all over the U.S. isn’t clay-concentrated, then how is CWD popping up in Canada, New Mexico and even Ohio?
VerCauteren’s research team recently finished a study that found crows – avian scavengers – to be responsible for moving CWD around because they feast on dead animals.
“We found that if positive material goes into the front end of a crow, what comes out the back end of the crow is infectious,” VerCauteren said.
Since cervids are already spreading CWD just by eating, excreting and dying in nature, it becomes problematic that crows are potentially spreading the disease, too.
Then what happens next?
Since research is still uncovering the how’s and why’s of CWD, one way to potentially manage a disease is through controlling the amount of infected individuals.
“In the wild, when animals exist at really high density, there’s a good reason to believe that transmission rates are going to be higher, not only for CWD, but all kinds of disease,” Hobbs explained.
That is where hunters come in.
Mark Vieira, a terrestrial biologist at the Colorado Division of Wildlife said in, 2001 to 2005 they greatly liberalized hunting licenses in northern Larimer County so they could manage cervids, in particular female mule deer.
“We attempted to lower the prevalence and stop the spread of CWD,” Vieira said. “To fast forward, we were unsuccessful in stopping the spread because now we have detected it in much of the state and the prevalence hasn’t gone down.”
During that time, Vieira explained the DOW extended the hunting season and also offered two for one carcass tags for hunters. He said that hunters could buy up to four tags, so if they were able to they could harvest eight does in one season.
“People were camped out there wanting the licenses,” he said. “That year, in 2002, we harvested 1,200 does in northern Larimer County with hunters. Now, in 2009 we’re going to harvest between 70 to 90 does.”
But this strategy, as Vieira explained, did not work and they had to reevaluate their management plan because even though they reduced the herd in northern Larimer County the DOW did not see CWD prevalence rates drop.
During 2002, when mad cow disease was a headline mainstay, VerCauteren explained there was a lot of paranoia surrounding CWD because the diseases are in the same family. This did not deter hunters from harvesting 1,200 does during that time of paranoia. And it was also mandatory for hunters to bring their harvested heads into the DOW for testing, Vieira said.
Now, however, it is a voluntary submission.
“Hunters can submit deer or elk heads, have them tested and it provides a way to survey units where we haven’t detected the disease in that area,” Vieira said. “If we have a stream of heads we can figure out the odds of what prevalence might actually be, based on hunter-harvested heads.”
Jeff Forsberg, a white tail deer hunter, said he has never worried about his harvests being infected with CWD, but still submits them for testing. Forsberg recently moved to Colorado from Minnesota where he worked in a butcher shop where hunters brought their harvests.
“It was interesting to see the results. In Minnesota some harvests were brought in from different geographic locations because we had a lot of animals from Canada in there,” Forsberg said. “A lot of people, though, did not pick up their meat and so we would donate it to a local food shelter.”
As a hunter, Forsberg explained that he has an obligation to not only kill something humanely and legally, but not to waste harvest because he wants to respect the outdoors and what he takes from it.
Josh Tashiro, a junior majoring in natural resources management at CSU, agreed that with hunting comes a great responsibility to be safe, which is why he only hunts on land belonging to friends of his.
“I’ve never dropped my elk heads [off for testing],” Tashiro said. “If I were to [hunt] off of my friend’s ranch, I probably would submit my harvest.”
Fred Quarterone, a wildlife manager at the DOW, said not all hunters submit their harvests now that it is voluntary.
“We have seen a reduction each year, but it’s a personal decision whether to turn [a head] in for testing,” Quarterone said. “A major reason some hunters do is because they want to know whether the animal they’re eating is infected or not.”
For Delwin E. Benson, a CSU professor in the fish, wildlife and conservation biology department and CSU Extension wildlife specialist, he said that it’s important for people to have more knowledge about CWD because even though there is no connection between humans and CWD, caution still needs to be there.
“It’s very important that people have an interest in wildlife and they need to know how to manage wildlife and part of that involves disease and preventing transmission,” Benson said.
As for the future of CWD, there is still a lot of research being done, and VerCauteren said they just developed a live rectal test for elk. This test enables them to detect CWD before the physical signs show up.
Even if humans may not be able to contract CWD, Hobbs said this problem demands our best attention.
“CWD is a serious environmental problem – even if it poses no risk to people, it poses grave threats to ecosystems throughout the world,” Hobbs said.
Tags: Volume 5 Issue 1
