Chronic Wasting Disease in Cervids

By Mark L. Drew, D.V.M.,Wildlife Veterinarian Idaho Department of Fish and Game January 26, 2001 Chronic Wasting Disease (CWD) is a disease that is present in the United States. It has been found in both captive and free-ranging cervids, including elk, mule deer and white-tailed deer. It is of importance to wildlife health because it is a newly recognized disease about which little information is known. It is of significant regulatory importance to domestic animal disease control agencies. Chronic Wasting Disease is included in a group of diseases known as Transmissible Spongiform Encephalopathies (TSE). Other similar diseases include Scrapie in sheep and goats, Bovine Spongiform Encephalopathy (BSE) in cattle, Transmissible Mink Encephalopathy (TME) in mink, and Creutzfeld-Jakob Disease (CJD), Fatal Familial Insomnia, Gerstmann-Straussler-Scheinker Syndrome (GSS) and Kuru in humans. CJD was first diagnosed in the 1920's and affects about one in one million people worldwide. Scrapie was first recognized in sheep in the 1700's. BSE was identified in cattle in Britain in about 1990. All of these diseases have long incubation periods, minimally 1.5 years to 5-10 years before the onset of clinical signs. All are fatal. The cause of these diseases is not known at this time, but all are presumed to be due to a group of proteins called prions (proteinaceous infectious particles) that appear to affect the ability of the brain and other tissues to function. Although these diseases are transmissible, they are not highly contagious. Humans are not thought to be capable of being infected with the TSE of animal origins with one exception. A new variant of Creutzfeld-Jakob Disease (nvCJD) has been found in approximately 80 individuals in Great Britain, two in Ireland and one in France and is associated with the consumption of meat from BSE infected cattle. CWD was first recognized in 1967 in a wildlife research facility in Fort Collins, Colorado in mule deer. Over the next 20 years, the disease has been diagnosed in about 100 animals in this facility and a wildlife research facility in Wheatland, Wyoming in mule deer, elk, white-tailed deer and black-tailed deer. A definitive diagnosis of CWD was established based on histopathology in 1978. In 1986, several free-ranging mule deer and elk in northeastern Colorado and southeastern Wyoming were diagnosed with CWD. Since that time, extensive opportunistic and hunter harvest surveys have revealed that CWD is present in about 5-6 percent of the mule deer and 2-3 percent of the free-ranging elk in the area. CWD has not been identified in other populations of free-ranging cervids in the USA despite testing of numerous animals. However, CWD has been diagnosed in captive elk kept on game farms. The disease has been found on farms in Saskatchewan, South Dakota, Nebraska and Oklahoma. Control and eradication programs are being developed by individual states and the federal government at this time to ensure that this disease does not pose further problems to farmed or free-ranging cervids. The disease has not been found in free-ranging or captive cervids in Idaho. Preliminary surveys of hunter-killed and road-killed animals are limited, but no evidence has been found that the disease is present in free-ranging populations of cervids in the state. The Idaho Department of Fish and Game has embarked on a targeted surveillance program wherein deer or elk that are observed or reported with clinical signs that may be associated with CWD (emaciation, abnormal behavior, etc.) are euthanized and tested. In addition, some hunter-killed animals have been tested. Specifically, 47 animals were tested in 1997; 31 were tested in 1999 and eight were tested in 2000. No animals have tested positive for CWD to date. All samples have been tested at the Wyoming State Diagnostic Laboratory, Laramie, Wyoming. Future testing plans include collection of samples from road-killed deer and elk in late winter and spring of 2001 and collection of samples from deer and elk harvested by hunters in fall of 2001. Specific training of IDFG personnel in recognition of suspect CWD animals and collection of appropriate samples is limited. Training sessions were conducted prior to the collection of samples from hunter-killed animals in 1997. Further training of IDFG personnel is planned for later this winter and early spring. The Idaho State Department of Agriculture has temporary rules in place that require mandatory testing of all elk older than 16 months of age that die on elk farms and testing of 25% of the elk that either go through slaughter facilities or are harvested on shooting operations. A voluntary certification program for elk farmers is in place, although full certification of any facility will take a minimum of 5 years. No evidence of this disease has been detected in the limited number of animals examined to date. The important message to be delivered is that CWD is a serious concern for ISDA and IDFG. Surveillance for the disease is being conducted by both agencies. Staff training is going to be done in the near future. A more generalized sample collection and testing program will be conducted in 2001. Funding ($35 per sample for testing and unknown collection costs) must be sought to enable the surveillance efforts to go forward. To date, there is no evidence that CWD is present in Idaho in either free-ranging or captive deer or elk.