Posted on 04/11/2002 10:19:10 PM PDT by ATOMIC_PUNK
D E N V E R, April 11 — Colorado wildlife officials have killed more than 1,720 elk since last fall to stanch the spread of a fatal brain illness related to mad cow disease.
Known as chronic wasting disease, the illness has been found in 44 elk on nine ranches, state Agriculture Department spokeswoman Linh Truong said Wednesday.
State veterinarian Wayne Cunningham said one ranch may have been infected as early as 1992. The disease also has been found in Colorado deer.
Wildlife officials have killed both wild and domestic elk that were in contact with infected animals, or at ranches where the disease was found.
Chronic wasting causes animals to grow thin as it destroys their brains. It is related to bovine spongiform encephalopathy, or mad cow disease. There is no test to determine if live elk are infected.
It is not known to spread from animals to people but scientists say that cannot be ruled out.
Veterinary Services
October 2001
Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy (TSE) of deer and elk. To date, this disease has been found only in cervids (members of the deer family) in North America. First recognized as a clinical "wasting" syndrome in 1967 in mule deer in a wildlife research facility in northern Colorado, it was identified as a TSE in 1978. CWD is typified by chronic weight loss leading to death. There is no known relationship between CWD and any other TSE of animals or people.
In the mid-1980s, CWD was detected in free-ranging deer and elk in contiguous portions of northeastern Colorado and southeastern Wyoming. In May 2001, CWD was also found in free-ranging deer in the southwestern corner of Nebraska (adjacent to Colorado and Wyoming). The limited area of northern Colorado, southern Wyoming, and southwestern Nebraska in which free-ranging deer and/or elk
positive for CWD have been found is referred to as the endemic area. Soon after diagnosis of the
disease as a TSE, Colorado and Wyoming wildlife management agencies stopped the movement of deer and elk from their research facilities; wild cervids have not been translocated from the endemic area.
CWD also has been diagnosed in farmed elk herds in a number of States and in one Canadian province. The first positive farmed herd in the United States was detected in 1997 in South Dakota. Since then, 16 additional positive herds have been found: South Dakota (6), Nebraska (3), Colorado (5), Oklahoma (1), and Montana (1). As of October 2001, 6 of these 17 positive herds remain under State quarantine. Ten of the herds have been depopulated or have been slaughtered and tested, and the quarantine has been lifted from one herd that underwent rigorous surveillance with no further evidence of disease. CWD also has been found in farmed elk and free-ranging mule deer in the Canadian province of Saskatchewan. For more information on CWD in Canada visit the Canadian Food Inspection Agency Web site at www.inspection.gc.ca/english/anima/heasan/disemala/cwdmdce.shtml.
Species that have been affected with CWD include Rocky Mountain elk, mule deer, white-tailed deer, and black-tailed deer. Other ruminant species, including wild ruminants and domestic cattle, sheep, and goats, have been housed in wildlife facilities in direct or indirect contact with CWD-affected deer and elk with no evidence of disease transmission. There is ongoing research to further explore the possibility of transmission of CWD to other species.
Causative Agent
The agent responsible for CWD (and other animal TSEs, such as scrapie and bovine spongiform encephalopathy) has not been completely characterized. There are three main theories on the nature of the agent that causes CWD: (1) the agent is a prion, an abnormal form of a normal protein, known as cellular prion protein, most commonly found in the central nervous system. The abnormal prion protein "infects" the host animal by promoting conversion of normal cellular prion protein to the abnormal form; (2) the agent is an unconventional virus; (3) the agent is a virino, or "incomplete" virus composed of nucleic acid protected by host proteins. The CWD agent is smaller than most viral particles and does not evoke any detectable immune response or inflammatory reaction in the host animal. Based on experience with other TSE agents, the CWD agent is assumed to be resistant to enzymes and chemicals that normally break down proteins, as well as resistant to heat and normal disinfection procedures.
Clinical Signs
Most cases of CWD occur in adult animals. The disease is progressive and always fatal. The most obvious and consistent clinical sign of CWD is weight loss over time. Behavioral changes also occur in the majority of cases, including decreased interactions with other animals, listlessness, lowering of the head, blank facial expression, and repetitive walking in set patterns. In elk, behavioral changes may also include hyperexcitability and nervousness. Affected animals continue to eat grain but may show decreased interest in hay. Excessive salivation and grinding of the teeth also are observed. Most deer show increased drinking and urination.
Diagnosis
Research is being conducted to develop live-animal diagnostic tests for CWD. Currently, definitive diagnosis is based on postmortem examination (necropsy) and testing. Gross lesions seen at necropsy reflect the clinical signs of CWD, primarily emaciation. Aspiration pneumonia, which may be the actual cause of death, also is a common finding in animals affected with CWD. On microscopic examination, lesions of CWD in the central nervous system resemble those of other TSEs. In addition, scientists use a technique called immunohistochemistry to test brain tissue for the presence of the abnormal prion protein to diagnose CWD.
Epidemiology
The origin and mode of transmission of CWD is unknown. Animals born in captivity and those born in the wild have been affected with the disease. Based on epidemiology, transmission of CWD is thought to be lateral or from animal to animal; although maternal transmission may occur, it appears to be relatively unimportant in maintaining epidemics.
Surveillance
Surveillance for CWD in free-ranging deer and elk in Colorado and Wyoming has been ongoing since 1983, and to date, has confirmed the limits of the endemic areas in those States. CWD in free-ranging deer in Nebraska was detected in 2000/2001; more intensive surveillance to better define the prevalence and distribution of the disease in free-ranging deer in Nebraska is underway. In addition, an extensive nationwide surveillance effort was started in 1997-98 to better define the geographic distribution of CWD in free-ranging cervids in the United States. This surveillance effort is a two-pronged approach consisting of hunter-harvest cervid surveys conducted in many States, as well as surveillance throughout the entire country targeting deer and elk exhibiting clinical signs suggestive of CWD. Over 15,000 harvested free-ranging deer and elk have been tested to date, including over 8,000 animals harvested from outside of the endemic area. In the United States no CWD-positive free-ranging animals have been found outside of the endemic area.
Surveillance for CWD in farmed elk began in 1997 and has been a cooperative effort involving State
agriculture and wildlife agencies and the U.S. Department of Agriculture's (USDA) Animal and Plant Health Inspection Service (APHIS). Farmed cervid surveillance has been increasing each year since 1997 and will be an integral part of the USDA program to eliminate CWD from farmed elk.
Gov. Bill Owens on Tuesday named a 10-member task force that will monitor efforts by the Division of Wildlife and the Department of Agriculture to contain Chronic Wasting Disease.
The task force will make recommendations to the agencies as well as to Owens, who said he intends to share research with the eight other governors whose states are beset with CWD.
The group will be co-chaired by Department of Natural Resources Executive Director Greg Walcher and state Agriculture Commissioner Don Ament.
Other members are:
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