Chronic wasting disease for the first time has been found in the heart muscle of white-tailed deer and elk, according to researchers in the University of Wyoming’s College of Agriculture.
The finding is important to wildlife managers, hunters and scientists because the cardiac muscle — which comprises meat — of big-game animals susceptible to CWD is consumed by humans.
Hunters, however, should not be alarmed, said Jean Jewell, a research scientist in the UW Department of Veterinary Sciences.
“There is a tendency for people to become alarmed when they hear something that makes them think their health might be at risk, but at this stage there is no evidence to suggest humans are susceptible to CWD,” Jewell said.
That does not mean hunters shouldn’t take precautions, according to the Wyoming Game and Fish Department (G&F). They are advised not to kill or eat animals that appear sick, and it is recommended they wear long, disposable rubber or latex gloves when field dressing animals. This will help protect them from not only CWD but other diseases.
Meat should be removed from bones when butchering, according to G&F.
The Centers for Disease Control and Prevention and the World Health Organization recommend animals testing positive for CWD not be consumed, according to a two-page brochure on CWD recently published by the G&F.
The brochure is available at G&F district offices across Wyoming and includes regulations governing the disease in the state, where it has been found, management efforts and how hunters can protect themselves and help prevent the spread of the disease.
An electronic copy is available on the Wyoming State Veterinary Laboratory’s (WSVL) Web site at http://wyovet.uwyo.edu/Diseases_2006.asp. The Department of Veterinary Sciences manages the WSVL, where the research took place.
G&F wildlife disease specialist Hank Edwards said the highest concentration of CWD in Wyoming occurs in the southeast corner of the state. “That’s where we’ve historically found it and continue to find it. In the last two years, it was also discovered in the Kaycee, Worland, Thermopolis and Newcastle areas,” he said.
In areas where CWD is known to occur, Jewell noted, hunters are advised not to consume brain, spinal cord, lymph nodes or heart. She said thorough cooking kills many pathogens, but prions are not destroyed by cooking.
CWD is a chronic, fatal disease of mule and white-tailed deer, Rocky Mountain elk and moose. It belongs to the group of diseases called transmissible spongiform encephalopathies (TSEs), which are thought to be caused by prions.
A prion is a microscopic protein particle lacking nucleic acid. It is thought to be the infectious agent responsible for CWD, the other animal TSEs (including scrapie in domestic sheep and bovine spongiform encephalopathy [BSE], also known as “mad cow” disease, in cattle), and other degenerative diseases of the nervous system. There is no evidence CWD is transmissible to livestock, Jewell said.
Jewell and UW research partner Jeremy Brown said their finding of abnormal prion proteins in the heart tissue of elk and white-tailed deer raises additional questions.
“This study has opened some interesting avenues for further research, such as delving further into the pathology of the disease and following it down through the nervous system,” Brown said. For instance, he asked, why was CWD detected in only the heart muscle and not other muscle tissues of the infected white-tailed deer and elk?
Why wasn’t the disease found in the heart muscle of CWD-infected mule deer?
Jewell and Brown detected seven CWD-positive heart samples from 16 captive and one free-ranging white-tailed deer infected with the disease. They also detected CWD in the heart muscle of 12 of 17 captive elk that were infected.
“This is the first report of disease-associated prion protein in the cardiac muscle tissue of ruminants infected with a TSE,” said Jewell, who carried on the research started in 2003 by the late Beth Williams, a professor in the Department of Veterinary Sciences, and Terry Kreeger, adjunct professor in the department and supervisor of the G&F’s Veterinary Services Branch.
“This had not been seen before in any of the animal prion diseases,” Jewell said. Previously, she said, CWD had been detected in the lymph nodes and nervous systems — including the brain and spinal cord – of white-tailed deer, mule deer and elk.
Jewell said other parts of infected deer can contain very small amounts of CWD prions that can only be detected by sensitive bioassays. Bioassay is the determination of the strength of a biological activity of a substance, such as a drug or hormone, by comparing its effects with those of a standard preparation on a test organism.
CWD has been diagnosed in wild deer and elk in 10 states, including Wyoming, and two Canadian provinces, said Cynthia Tate, G&F assistant wildlife veterinarian.
One of the most recent cases was detected by the WSVL Sept. 29 and involved an elk killed by a hunter in the Shirley Mountains northwest of Medicine Bow in southeastern Wyoming. Animals show no apparent signs of illness throughout much of the disease course. In terminal stages of CWD, animals typically are emaciated and display abnormal behavior.
Hunters taking animals in the CWD areas identified in the G&F regulations should consider submitting samples of deer, elk or moose to the WSVL or G&F for testing, Jewell said.
The WSVL fee is $25, and results are typically known within two weeks. The G&F does not charge for testing, but it will only test animals based on where they were harvested and what the current department needs are, Edwards said.
The Wyoming Wildlife/Livestock Disease Research Partnership and the International Association of Fish and Wildlife Agencies contributed $100,000 to a number of CWD projects started by Williams, including the one just completed.
Helping with the project by Jewell and Brown were Paula Jaeger, Mercedes Thelen, Todd Cornish and Don Montgomery with the Department of Veterinary Sciences; Edwards and Kreeger with the G&F; and Michael Miller with the Colorado Division of Wildlife.
A report of these findings is being published in the November edition of Journal of General Virology. Authors are Jewell, Brown, Kreeger and the late Beth Williams.