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October 24, 2012

Chronic Wasting Disease

An emerging threat

Chronic wasting disease is a progressive, fatal disease threatening captive and wild populations of deer and elk in certain areas of the United States. There is concern that this disease may spread further and affect more deer, elk, and/or moose herds. As a result, CWD has important scientific and political implications.

What is chronic wasting disease?
Where did CWD originate and how is it transmitted?
Whom does CWD affect?
What can be done?

 

What is chronic wasting disease?

CWD is a transmissible spongiform encephalopathy affecting deer and other cervids (animals belonging to the deer family). Abnormal proteins called prions attack the nervous system and brain of the infected animal. As CWD progresses, symptoms include reduced eating and weight loss, repetitive walking, possible blindness, excessive drinking, fine head tremors, loss of coordination, and increased salivating. The disease is fatal to infected animals.

Where did CWD originate and how is it transmitted?

CWD was first identified in captive mule deer in Colorado in the late 1960s. It was not observed in the wild until 1981. However, the origin and cause of the disease have never been definitively determined. Most wildlife scientists agree that CWD proliferated in captive herds. In fact, when CWD has been present in a captive population for over two years, over 90% of the animals will be infected. The disease is directly transmissible via saliva, urine, feces, blood, and muscle and is highly infectious.

 

Whom does CWD affect?

CWD has been found in populations of elk and deer on game farms in 22 states, Canada, and South Korea (see a PDF map of CWD in the United States). Captive populations of these cervids have tested positive for this disease in 13 of these states. In 2012 alone, CWD was discovered for the first time in Texas, Iowa, and Pennsylvania. To date, there is no proof of human infection, and scientists still do not understand the potential risk to humans.

 

What can be done?

Most importantly, to halt the continuing spread of the disease all states must cease the importation and exportation of cervids. Banning the transport of cervids will help to contain the disease and prevent further dissemination by the game farming industry. Canada has already prohibited the importation of cervids from the United States, and several states have banned the practice as well.

In order to reduce the potential of future biological threats from this and other zoonotic diseases on a larger scale, states must ban game farms and captive hunts. The high population densities that characterize captive hunt facilities greatly increase the risk of disease transmission. Animals are frequently fed at feeding stations, where salivary contact is inevitable—resulting in the infection of all penned animals from a single diseased individual. Furthermore, although there must legally be fencing around captive hunt ranches, animals often can and sometimes do escape from these facilities. In an effort to protect animals and the public, twenty-six states have already enacted full or partial bans on captive hunts.

The risk of CWD spreading to native populations of wildlife is taken very seriously. Thus far, testing and "depopulating" are the chosen methods of eradication. This method can be complicated because only deceased animals can be tested for CWD. CWD also has a long latency period, which means that the animals may not even show any symptoms of the disease for a long period of time. After one wild deer tested positive for CWD in early 2011, officials with the Minnesota Department of Natural Resources shot 1,180 deer within a ten-mile radius in response. Certain states such as Colorado have rightly concluded that eradicating entire populations of wild animals is neither feasible nor efficient in stopping the disease. The state of Wisconsin has already spent over $35 million since 2002 in response to CWD outbreaks in the state.

Sources

Department of Agriculture. Office of the Secretary. "Declaration of Emergency Because of Chronic Wasting Disease." Docket # 01-019-1.

Herring, Hal. "Disease is Wasting the West's Wild Herds." High Country News 27 Sept. 1999.

Rose, Julie. Chronic Wasting Disease and Cervid Regulations by State within the United States. Michigan Department of Natural Resources. April 2002.

Visit the CDC website for more information: www.cdc.gov/ncidod/dvrd/cwd/.

United States Department of Agriculture. "USDA and DOI Announce Formation of Joint Chronic Wasting Disease Working Group." USDA News Release No. 0195.02.

Williams, Elizabeth S., Michael W. Miller, E. Tom Thorne. "Chronic Wasting Disease: Implications and Challenges for Wildlife Managers." Presented paper.

Updated June 10, 2011

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