Chronic wasting disease of deer and elk: a call for national management.

• Author: Opsahl, Ronald W.

1. INTRODUCTION II. A PRIMER ON CHRONIC WASTING DISEASE A. Prion Diseases: What Are They? B. History and Distribution of Chronic Wasting Disease C. Diagnoses and Treatment D. Implications for Wildlife Managers III. ALTERNATIVE LIVESTOCK OPERATIONS A. Game Ranching and Farming in North America B. Management of Game Ranches and Farms IV. MANAGEMENT OF CWD: PAST AND PRESENT A. Models for Preventing CWD Introduction into Captive Cervid Herds B. CWD Detection in Free-Ranging Deer and Elk C. Other CWD-Related Regulations D. Responses to CWD Once Detected E. Federal Management Thus Far V. SUGGESTIONS FOR FUTURE CWD MANAGEMENT A. Authority for Federal Management B. Federal Permits for Alternative Livestock Operations 1. Prevention of Introduction 2. Isolation of Captive Herds 3. Surveillance and Depopulation of Infected Herds C. Recommendations for Uniform State Management VI. CONCLUSION I. INTRODUCTION

   Chronic wasting disease (CWD) is an infectious, naturally occurring, always fatal, progressively degenerative, neurological disease affecting at least three members of the deer family (Cervidae or Cervid) (1) that is spreading in several states. (2) As a result, state and federal governments and private organizations are scrambling to develop management plans and implement legislation and regulations to control the disease. (3) Without a forceful regulatory response, CWD will likely lead to significant declines in cervid populations, increases in state and federal management expenditures, and significant negative economic impacts to rural communities that depend on wildlife-related recreation. (4)

   Although CWD is endemic to northeastern Colorado, southeastern Wyoming, and northwestern Nebraska, recently the disease has spread well beyond the endemic area. (5) Chronic wasting disease has been identified in at least 12 states and 2 Canadian provinces--Colorado, Illinois, Kansas, Minnesota, Montana, Nebraska, New Mexico, Oklahoma, South Dakota, Wisconsin, Wyoming, and most recently Utah in the United States; Alberta and Saskatchewan in Canada. (6)

   The recent spread of the disease into non-endemic areas is probably associated with the sale and transport of domestic deer and elk from contaminated alternative livestock facilities--also known as game ranches or farms. (7) Alternative livestock operations represent a significant business in North America; for example, in 1996, there were approximately 60,000 deer farmed in North America on more than 100 venison-producing livestock operations. (8) In addition to deer, elk are farmed extensively throughout North America; there are an estimated 160,000 elk in captivity on 2,300 U.S. and Canadian elk ranches. (9) Since 1997, CWD has been detected in at least 24 privately owned elk herds in 8 states. (10) Private game ranches are thought to be the source of many of the outbreaks in free-ranging cervid populations in non-endemic areas--known as "spillover" infections. (11) These spillover events likely occur either via 1) captive animals escaping and infecting the wild population, 2) free-ranging animals entering the enclosure and then being released after infection, or 3) some level of contact through the enclosure fencing which leads to infection.

   Unlike most infectious diseases, CWD does not appear to have an equilibrium point at which the disease ceases to increase in prevalence and coexist with uninfected populations. (12) The disease appears to either result in continuously increasing disease prevalence within the local cervid population or, if population densities are sufficiently low, an eventual loss of CWD from the population. (13) Population modeling only showed a loss of CWD from the simulated population when an extensive, selective cull (i.e., removal and destruction of target animals in specific locations) occurred, thereby reducing the transmission rate or resulting in the death of the infected animals before transmission could occur. (14)

   The implications of these models are troubling. If left unchecked, CWD will result in the loss of significant free-ranging deer and elk herds. As these heavily infected populations die out, newly infected populations--either at the edge of the heavily infected population or infected through human-induced disease introduction (i.e., animal translocation)--will continue to provide a source of infection, leading to the persistence and spread of the disease. (15)

   The potential impacts to local economies are staggering. Both consumptive and nonconsumptive users of deer and elk contribute more than $20 billion annually to agency budgets and local economies through direct and indirect spending. (16) Additionally, tens of millions of dollars are spent annually in CWD cleanup and research. (17)

   Thus far, state laws have had little effect in stopping shipments of animals from contaminated facilities, largely because the disease has a prolonged incubation period (18) and state monitoring programs for the disease are relatively new to the industry. (19) In addition, there are no test methods available for testing live animals for CWD; the only definitive diagnostic involves sampling brain tissue postmortem. (20) As a result, captive deer and elk that may have been exposed to the CWD contagion prior to the state surveillance program are not barred from interstate commerce if the symptoms of CWD have not yet arisen in the source herd. If all interstate transportation of deer and elk were stopped today, the resulting disease spread still would not be completely known for at least five years. (21)

   As a result of the dramatic spread of CWD, Congress has proposed several pieces of legislation (22) and state agencies are implementing emergency regulations and response plans. (23) Unfortunately, these efforts are primarily reactive and little consistency among state programs exists. (24) After a brief overview of the disease, this Comment examines regulations limiting the transportation of animals from alternative livestock facilities, assesses state and federal legislation, agency policies, and public concerns in dealing with the spread of CWD, and proposes aggressive, nationally uniform regulations designed to halt further spillover CWD outbreaks.

2. A PRIMER ON CHRONIC WASTING DISEASE

   1. Prion Diseases: What Are They?

      Chronic wasting disease is a member of a relatively rare group of diseases known as transmissible spongiform encephalopathies (TSEs) or priori diseases. (25) Other TSE diseases include scrapie in domestic goats and sheep; (26) transmissible mink encephalopathy in domestic mink; (27) Creutzfeldt-Jakob Disease (CJD) (28) and variant CJD (vCJD) (29) in humans; and bovine spongiform encephalopathy (BSE) in cattle, commonly referred to as mad cow disease. (30)

      The specific causes of TSEs remain unknown; however, the accepted theory is that the disease follows the infection of abnormal prion proteins, which spontaneously replicate and accumulate in the brain, ultimately causing neurologic symptoms. (31) Priori proteins are normally found in nervous and lymphoid tissues of all mammals; however, in TSEs, an abnormal prion develops in an altered configuration--the abnormal prion is folded into a structure that is physically different from the normal prion. (32) The resulting configuration is resistant to the normal degradation processes of the body and is apparently capable of self-replication. (33) This self-replication process continues in a chain reaction, resulting in a buildup of abnormal prions in the central nervous system. (34) Degenerative changes in the brain follow, (35) including characteristic lesions (i.e., multitude small "holes" in the brain), resulting in a sponge-like appearance from which all "spongiform" diseases gain their names. (36)

      While the TSEs behave like infectious diseases, that is they are capable of being transmitted between animals, TSE agents appear to have no genetic identity. (37) Therefore, the prion contagion is more correctly classified as a unique type of toxicity rather than a biologic infection. (38) In addition, the prion agent has a remarkable resistance to a wide range of environmental conditions and can withstand a range of treatments that would kill or inactivate conventional infectious agent. (39) This makes the treatment and control of TSE outbreaks more difficult. (40)

      Although the intensity of symptoms varies between individual cases, a discernable group of symptoms normally present in all TSEs. As the abnormal prion accumulates in the brain and the spongiform process progresses, the infected individual gradually undergoes behavioral changes, including dementia, ataxia (loss of motor control), and mild to severe tremors. (41) As the disease progresses, the affected animal undergoes a loss of body condition and may decrease interaction with the animal handler or other members of the herd.42 There is no treatment for animals affected by TSEs and the degeneration continues, ultimately resulting in death. (43)

   2. History and Distribution of Chronic Wasting Disease

      A "chronic wasting disease" was first identified in mule deer held at a research facility in northern Colorado in the late 1960s. (44) In 1978, chronic wasting disease was categorized as a TSE through histopathology. (45) Following these initial diagnoses in captive mule deer, CWD was identified in captive elk, (46) free-ranging elk, (47) free-ranging mule deer, (48) and free-ranging white-tailed deer. (49) Although CWD was not detected in free-ranging deer populations until the mid- to late-1980s, disease modeling suggests that CWD may have been present in some free-ranging deer populations for twenty years or more before it was first detected. (50)

      Chronic wasting disease is considered endemic to a relatively small area in northeastern Colorado, southeastern Wyoming, and western Nebraska. The endemic area is a roughly 40,000 square-kilometer (15,444 square-mile) area bordered by the North and South Platte Rivers and is home...