DOW develops live test for CWD in deer herds

DOW develops live test for CWD in deer herds

December 13, 2001

By the Colorado Division of Wildlife

DENVER — A test for chronic wasting disease that samples tonsil tissue from live mule deer has been developed by the Colorado Division of Wildlife, providing a new tool to help prevent the spread and reduce the prevalence of the disease in wild and captive deer herds.

The division, working with Colorado State University in Fort Collins and the University of Wyoming in Laramie, began a research project earlier this year to determine if the live test would be accurate and effective.

"The availability of a reliable test for diagnosing CWD in live mule deer offers us several opportunities for advancing both the understanding and management of this important wildlife disease," said DOW veterinarian Mike Miller, who led the study in collaboration with DOW researcher Tom Hobbs.

"Early detection and removal of CWD-infected animals appears to be the most effective method for managing CWD," Miller said. "Selective culling of positive animals and animals in contact with these positive individuals should help reduce the prevalence rates in endemic areas."

Miller cautioned that the new test will not work in all situations and won’t replace the current testing of animals after they have been killed by hunters or wildlife managers.

"Despite some promising aspects, we recognize the test’s practical limitations," Miller said. "The need to capture, anesthetize and precisely sample individual deer limits the broad implementation of this testing approach in managing free-ranging deer populations infected with CWD.

"At best, this approach may find applications in augmenting disease-management efforts based primarily on reducing deer density in endemic areas."

Miller estimated that the process of tranquilizing, taking samples, collaring and releasing animals pushes the cost to more than $200 per animal.

The new test is also more sensitive than examining the brain tissue - the current standard test for CWD - because prions congregate in the tonsils early in the disease’s development. Testing of tonsil tissue is equally effective in both live deer and deer that have been killed by hunters or during culling efforts.

The testing of tonsil tissue appears to also be effective in white-tailed deer that also inhabit portions of Colorado, Wyoming and other Western states. But the test isn’t effective for elk because the disease develops differently in the two species. There continues to be no live test for elk.

Chronic wasting disease is a fatal ailment found in wild deer and elk in northeastern Colorado and southeastern Wyoming. Two deer with CWD have been found in extreme northwestern Nebraska and two were found in western Saskatchewan earlier this year.

The disease – thought to be caused by an aberrant, infectious protein - was first noted as a syndrome in the 1960s and first identified as a transmissible spongiform encephalopathy in the early 1980s. About 5 percent of deer and less than 1 percent of elk are infected with CWD in the endemic areas. CWD had never been found in wild deer and elk in other portions of Colorado.

There is no known cure and researchers don’t know how the disease began.

Research was conducted last spring and summer on 160 mule deer in the Estes Park and Livermore areas along Colorado’s northern Front Range. The effort began because researchers knew from earlier studies that prions accumulate in the tonsils early in the disease and remain in the animal.

The tests involve tranquilizing deer, taking a biopsy from the animals’ tonsil, then collaring and releasing the deer. The biopsies are then analyzed in a laboratory.

Miller said the new test may be particularly useful where hunting doesn’t occur, such as urban and suburban areas and inside Rocky Mountain National Park. Test results may also allow wildlife managers to determine if the illegal feeding of deer is contributing to the spread of the disease. Artificial feeding causes animals to congregate in small areas, increasing the chance that disease will spread. Anecdotal evidence points to feeding as a major factor in the disease’s relatively high prevalence in urban areas and subdivisions in Estes Park and locations northwest of Fort Collins.