CWD TESTING AT THE WISCONSIN VETERINARY DIAGNOSTIC LAB IN MADISON
Submitted by Brian Wolf
Have you ever wondered why it can take a couple of weeks before you get your results back after submitting an Elk brain sample for CWD testing? This question and others were put to veteriniansDr. Dan Bahr and Dr. Keith Poulson of the Wisconsin Veterinary Diagnostic Lab in Madison, WI
Interviewer: Dr Paulson, why do deer hunters during hunting season get their CWD results within a few days, while elk producers can wait weeks to get their test results?
Dr. Paulson: There are 2 different tests that can be done to specimens for CWD. 1 of the tests, the “Elisa” is performed on blood. This is the test which is performed on white tail deer and this test can be run daily, depending on the season. During gun season, this test is run more frequently due to the large number of samples.
The other is the “Cervid-IHC” test which is performed on a tissue sample and this is performed weekly. This test is used for the submitted elk brain samples and is only performed weekly due to the smaller number of samples. Submitted samples are batched and performed once a week because it is more cost effective.
Interviewer: OK. So the IHC test is only done weekly. Still it seems like producers wait 2-3 weeks for their results.
Dr. Paulson: This can be due to a number of factors. The test is done on Tuesday morning after the UPS
Shipment arrives. Therefore, if a specimen sample arrives on Wednesday, it is batched with the following weeks testing.
Secondly, the IHC method involves more processing. The specimen must be fixed in formalin, sectioned, stained and then read by the lab histologist. This is usually a 2-3 day process. Therefore a sample which arrives at the lab on Tuesday morning will not have the results posted until Thursday or Friday of that week.
Interviewer: So if the IHC test was performed more than once a week so that test results would be obtained faster, it would be more expensive.
Dr. Paulson: This is correct. It is more cost effective for the taxpayer if the testing is batched and performed weekly.
Interviewer: When is the best time to ship a sample for testing?
Dr. Paulson: If shipped by UPS Ground – Overnight the cost is $7.00 and the testing process begins on Tuesday after shipment is received.
Interviewer: What happens if the test shows a positive result?
Dr. Paulson: The positive result is submitted to the USDA and the state Veterinarian.
Interviewer: Why are samples submitted from 2 sites, the Obex and Lymph nodes?
Dr. Poulson: One result is confirmed by the second. Also, sometimes the wrong gland may be sent. The lymph nodes look a lot like the salivary gland and sometimes the salivary gland may be sent.
Interviewer: Some producers have taken a class and are allowed to submit their own samples.
Have you noticed any problems with this?
Dr. Poulson: What we find is that the chances of error are less with more experience. If the producer or veterinarian only submits 2 specimens a year, the chances are higher that the wrong tissue may be submitted.
Interviewer: What affects the quality of a submitted specimen?
Dr. Bahr: The main factor is time after death. The longer and warmer the animal, the faster the decomposition. However if the animal would be positive for CWD, even the decomposed sample would test positive because the the prion is very stable and doesn’t decompose.
Interviewer: How many CWD tests are performed each year by your lab?
Dr Bahr: The lab performs around 8,000 Elisa tests and 10,000 IHC tests each year on deer and elk. Other similar tests performed are for scrapies in sheep and BSE in cattle.
Interviewer: Do you have a website and what do you find there?
Dr. Poulson: The website is “WVDL.Wisc.edu. The website contains test results, the hundreds of tests we perform, and the fees we charge. Also there are links to recent articles, such as the “Reintroduction of Elk into Wisconsin”.
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