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Environmental Persistence of Chronic Wasting Disease Exacerbates Deer Population Declines

U.S. Geological Survey

Washington, DC --(Ammoland.com)- Long-term impacts of the chronic wasting disease (CWD) epidemic in North American deer, elk and moose will depend on how the disease persists in the environment, according to a new U.S. Geological Survey study.

The study examines how the persistence of CWD in the environment affects future deer populations using computer simulations.

Like other “prion” diseases, CWD is caused by unusual, infectious proteins called prions; it is a fatal neurological disease of deer, elk and moose. One of the best-known of these prion diseases is “mad cow” disease, a cattle disease that has infected humans. However, there is no evidence that CWD has infected humans.

Prions can be transmitted directly through animal-to-animal contact, and indirectly through animals that come into contact with infected feces, urine and carcasses. Most current analyses assume that prions are transmitted through direct contact. The new study, however, demonstrates that indirect transmission – through uninfected animals coming in contact with contaminated material – is likely much more important in controlling the disease than previously thought.

“If indirect transmission is as important as our simulations show, then the projected long-term outcomes of CWD epidemics will be very sensitive to how long prions remain infectious in the environment,” said lead study author Emily Almberg, a former employee of USGS, and a current PhD student at Pennsylvania State University. “Disease management will need to consider both indirect and direct transmission.”

Previous studies have found infectious CWD prions in the environment for at least two years, and closely related sheep scrapie prions, another type of prion disease, have caused infections after 16 years. “If these two examples represent norms rather than exceptions,” said Almberg, “then our simulations suggest that CWD will reach higher peak prevalences and result in more extreme deer population declines.” In addition, indirect transmission and long-lived prions could complicate disease-control efforts.

According to USGS scientist Paul Cross, co-author of the study, “Our results show how the importance of the environmental reservoir may increase during the course of an epidemic, which may help to explain some of the differences we see among different regions that are in different stages of the epidemic.”

Since current management tools do not target reducing environmental transmission, the best prospects for CWD control may be very early in the epidemic when the traditional tools of culling deer are likely to keep direct transmission and overall infection levels at bay, the authors wrote.

CWD has been detected in 19 states and two Canadian provinces. Disease-causing prions, responsible for some incurable neurological diseases of people and other diseases in animals, are notoriously difficult to decontaminate or kill. Prions are not killed by most detergents, cooking, freezing, or by autoclaving, a method used to sterilize medical instruments.

The USGS study, Modeling Routes of Chronic Wasting Disease Transmission: Environmental Prion Persistence Promotes Deer Population Decline and Extinction, is available from the public accesses journal PLoS ONE, online.

Contact Information:
U.S. Department of the Interior, U.S. Geological Survey
Office of Communication
119 National Center
Reston, VA 20192 Leslie Allen 1-click interview
Phone: 406-994-7367

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CWD Not Found In Pennsylvania Hunter-Killed Deer Samples

Pennsylvania Game Commission

HARRISBURG, PA --(Ammoland.com)- Chronic wasting disease (CWD) was not found in samples taken from hunter-killed deer during the state’s 2010 hunting season, according to Dr. Walt Cottrell, Pennsylvania Game Commission wildlife veterinarian.

In 2010, 3,882 samples from hunter-killed deer were tested, and CWD was not detected. This marked the ninth year for testing hunter-killed deer. In total, nearly 30,000 deer have been tested. CWD was not detected in any samples from previous years.

Results showing that the CWD tests of hunter-killed elk from 2010 were all negative were announced on Jan. 5.

“We are pleased to report that Pennsylvania continues to have no confirmed or suspected cases of CWD in wild deer or elk,” Cottrell said. “By conducting these tests from a random sample of hunter-killed deer and on all hunter-killed elk, we continue our efforts to find the disease in wild deer and elk in the state.”

The CWD tests on deer and elk samples were conducted by the New Bolton Center, which is the University of Pennsylvania’s veterinary diagnostic laboratory. Under a contract with Penn State University, the elk samples also were tested for brucellosis and bovine tuberculosis and found to be free of those diseases.

Heads from hunter-killed deer were collected from deer processors by deer aging teams during the two-week rifle deer season. Specific tissues were collected from these heads at Game Commission region offices by agency personnel and Pennsylvania and U.S. departments of agriculture animal health officials.

“The test results are good news,” Cottrell said. “Although CWD has not been found in Pennsylvania, we must continue to be vigilant in our CWD surveillance efforts. The surveillance work we are doing is important for the early detection of CWD. Let’s not forget that CWD has been found less than 10 miles away from our border in Maryland, which is likely to be part of the spread of the disease from West Virginia. There is no reason to expect that it will not eventually come into Pennsylvania.

“We already are planning to continue testing hunter-killed deer and elk during the 2011-12 seasons, and we are pleased that the Pennsylvania and U.S. departments of agriculture will continue to play an important role in this disease surveillance program. However, we will also be increasing our surveillance by sampling road-killed deer adjacent to Maryland and investigating every clinically suspect deer that our time and budget allows.”

For more information on CWD and the state’s CWD-prevention plan, visit the Game Commission’s website (www.pgc.state.pa.us), click on “Wildlife” in the menu bar in the banner at the top of the page, then click on “Wildlife Diseases Home,” and choose “Chronic Wasting Disease (CWD).” Additional information on CWD can be found on the CWD Alliance’s website (www.cwd-info.org).

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