Wisconsin Veterinary Diagnostic Lab selects new CWD test

The Wisconsin Veterinary Diagnostic Laboratory, the state lab responsible for testing deer killed during Wisconsin’s annual hunt for the presence of chronic wasting disease (CWD), has selected a new rapid test for use beginning this November.

With its selection, the test, made by IDEXX, Inc., of Westbrook, Maine, will become the primary method by which the state screens tissue samples from deer for the presence of the agent that causes CWD, a fatal prion-caused disease that first surfaced in Wisconsin’s wild deer herd last year.

“The test was chosen based on the accuracy of its results, its ease of use in the laboratory and its ability to maximize the number of tests we can complete each week,” says Robert Shull, the lab’s director.

Between October 2002 and April 2003, the lab tested more than 35,000 samples of tissue using a more time-consuming test known as immunohistochemistry (IHC). At the time, according to Shull, IHC was the only available method with which the lab had sufficient experience to have confidence in test results.

The new assay, which was chosen from among five competing CWD assays, will be used during the upcoming hunting season to test frozen tissue from the lymph nodes of deer for the presence of CWD. The majority of CWD testing will be part of the statewide surveillance being conducted by the Wisconsin DNR and will involve samples from about 20,000 deer.

The IDEXX assay is currently undergoing the routine approval process by the U.S. Department of Agriculture, which must certify such tests before they can be used. Approval and licensure of the test is expected by November, Shull says. Until the new assay is approved, the lab will continue to analyze samples with the IHC process.

The IHC method, while accurate, is time and labor intensive, Shull says. “Performing 35,000 IHC tests for CWD last season took a Herculean effort, and we have now spent considerable time investigating alternative methods,” he says.

The Wisconsin Veterinary Diagnostic Laboratory, says Shull, is committed to providing high-quality and timely laboratory work at an affordable price for hunters and others wishing to have deer tested. “The choice of the new test is an example of our desire to meet that commitment,” he says.

Although there is no evidence that CWD is transmissible to humans, many hunters and consumers of venison have sought some indication that their deer are not CWD-positive. Testing for private hunters will be available on tissues collected by veterinarians throughout the state. The lab will test these samples by IHC because of the difficulty in shipping frozen samples, as required by all other CWD tests.