How did moose get CWD?
Star Valley deer, elk likely have the disease as well.
By Cory Hatch, Jackson Hole, Wyo.
October 29, 2008
Chronic wasting disease has likely infected Star Valley deer and elk herds, and the best option to slow its spread is to phase out feedgrounds in northwest Wyoming, a federal disease expert said Tuesday.
Tom Roffe, chief of wildlife health and a veterinarian for the U.S. Fish and Wildlife Service in Bozeman, Mont., made the comments a week and four days after Wyoming Game and Fish officials announced they found CWD in a moose near Bedford. The town in Star Valley is about 40 miles south of Jackson and the National Elk Refuge.
Game and Fish found the moose in February about 13 miles from the nearest state-run winter elk feedground. CWD wasn’t discovered in samples until recently, the state agency said.
The infected moose marks the first time CWD has crossed the Continental Divide into northwest Wyoming, where the state operates more than 20 elk feedgrounds. Artificial feeding critics say feedgrounds would promote the spread of the disease.
“The fact that this is in a moose means it’s probably in elk and deer,” Roffe said in a telephone interview from North Carolina, where he was attending a conference. More cases of CWD likely exist around Star Valley, because moose typically don’t migrate far, meaning the chances of the infected animal bringing the disease in from elsewhere is unlikely. Also, because moose have not typically been infected in areas where deer and elk have contracted CWD, the Star Valley discovery raises a host of new questions.
This is only the fourth documented case of CWD in moose. Chronic wasting disease is a cousin of “Mad Cow Disease” whose human form is Creutzfeldt-Jacob disease. While there is no known connection between CWD and the human form of the brain-wasting ailment, researchers have not ruled out a potential link.
The Centers for Disease Control recommends against eating any animal known to be infected.
Roffe said the chances of detecting the very first animal infected with a given disease are “astronomically against us.” That means the moose likely isn’t the only animal in the area that is infected.
“This is some distance from other areas with CWD,” he said. “When you find a moose like they did in this situation, it’s likely that [CWD] is already there.”
Roffe acknowledged that there is no conclusive study on the effects of CWD on a feedground but said most researchers feel the impact would be adverse. Elk are concentrated on feedgrounds more than when they forage naturally.
“I think that both sides of the issue would agree that feedgrounds aren’t going to improve the situation,” he said. “It’s going to make it worse for CWD. The question is: How much worse?”
Roffe pointed to a study of CWD-infected elk at Rocky Mountain National Park where the animals live in crowded conditions, although on native winter range, similar to feed grounds. That study showed an 11 percent infection rate. Roffe said, however, the testing method detects only about 75 percent of infected animals. “It’s probably more like 12 or 13 percent,” he said.
Wyoming’s feedgrounds, Roffe said, could exacerbate the situation. Once CWD is endemic to a given area, Roffe said there is very little wildlife managers can do to eliminate the disease, in part because the infectious prions, a defective protein that is at the root of the disease, can persist in the environment for several years.
“You have repeated use by a large number of animals in a small focal area,” he said of winter feedgrounds. “You’re going to have contamination of a long-lived prion agent.
Infected elk “are going to seed that ground,” he said. “You are going to be repeatedly reseeding that ground. You are going to enhance transmission cycles.” Roffe said there are options for “preventative wildlife disease management” before CWD becomes entrenched.
“I don’t think it’s too late [for Star Valley],” he said. “We have good information that says it’s over here on the west side, but it’s probably in low prevalence. The best thing for a feedground situation is that you don’t have them.”
Wyoming Game and Fish spokesman Eric Keszler defended the agency’s decision to keep operating feedgrounds. The state runs them to replace developed winter range, keep animals off private ranches and away from highways and sustain an excess population for hunters.
Some conservationists want the state to develop a plan that would eliminate elk winter feedgrounds as a defense against spread of CWD. They say feedgrounds could exacerbate the spread of the disease, possibly threatening a regional economy that has developed around elk, including a robust outfitting and hunting industry and tourism devoted to wildlife viewing.
Wyoming Game and Fish is monitoring hunter kills in the state, seeking samples of elk and moose that are killed. After disclosing discovery of the disease in the moose, the agency said it would increase its search for samples from wildlife in the Star Valley area.
“CWD is a different kind of disease, and there are a lot of things we don’t know about it,” Keszler said. “I think it’s accurate to say with most diseases, if you have animals in a higher concentrations like feedgrounds, you are going to have high prevalence rates of that disease.”
“On the other hand, we’re not convinced that CWD in an elk feedground population is going to be devastating to that population,” Keszler continued. “Some of the research we’re doing suggests that it won’t be.
“We still don’t know,” he said of how the disease will affect herds. “All that we can do is keep conducting surveillance and letting people know if we do find it or if we don’t find it.”
Keszler said there are significant problems with closing feedgrounds including a 60 percent to 80 percent reduction in the size of some elk herds and the likelihood of spreading brucellosis to cattle.
“We have serious concerns related to brucellosis,” he said. “If those animals aren’t on feedgrounds, they are going to be on ranches close to cattle.”
Brucellosis can cause undulant fever in humans. Health officials say hunters can eat the muscle tissue of brucellosis-infected game animals without worry about contracting brucellosis, which is hard to cure and sometimes fatal.
Bob Wharff, executive director of Wyoming Sportsmen for Fish and Wildlife, said the prospect of CWD in Star Valley is “scary.” His group is pro- hunting and believes in feedgrounds.
Detection of the disease doesn’t mean the feedgrounds should close, he said.
“It’s not the end all that some groups portray it as,” he said. “I’m more inclined to think that CWD has always been around.”
CWD remains a mysterious disease about which little is known, including how it is spread. There is no known cure or vaccine. It causes slow deterioration of the brain and ultimately death.