Question: About a month ago, there was an article in the Missouri Conservation Magazine about a new live test that can identify CWD in White-tail Deer. It has not been developed for elk yet. Could you do an article on it and let us know how much this test would cost along with how to take samples and where it is sent?

Answer: I have not read the article to which you refer, but the test you are asking about is likely a test that is done on lymphoid tissue, harvested from the live animal. Lymphoid tissue is found in lymph nodes and tonsils. Another, more convenient place to find lymphoid tissue is on the inside of the 3rd eyelid, which is that little “windshield wiper’ that slides across the eye from the middle corner. As you might guess, the function of lymphoid tissue is to collect foreign material and prevent invasion by disease. It has been found that sometimes lymph glands will contain prion proteins associated with CWD before they can be detected in the brain, and certainly before clinical signs of CWD appear. Since the lymphoid tissue can be sampled without killing the animal it appears to be a welcome candidate for a live animal test to detect CWD associated prions. However, the test is very much experimental and not available for commercial use.

In order for the test to be commercially useful, the test must be validated, and simple sampling techniques need to be developed. Tonsil tissue is the best tissue to sample, but not many deer would permit a tonsil biopsy when wide awake! This usually requires the deer to be under general anesthesia. A better place might be the 3rd eyelid gland, but while sampling is easier and can be performed on an awake deer, there is a limited amount of tissue available so that the test could only be done 2 or 3 times on a deer. Validation of the test means that the ability of the test to correctly identify diseased and non diseased animals must be worked out. A test that only identifies half of the infected animals tested is not useful, nor is a test that wrongly identifies healthy animals as infected.

You mentioned that the test has not been developed for elk yet. In fact, the test has been tried on elk enough to show that it doesn’t work as well as it does in deer. For some reason the prions in elk do not move into lymphoid tissue as well, or as rapidly as in deer.  CWD associated prions are often found in the brain of diseased elk before they appear in lymph tissue. By that time the elk is either clinically ill or has been shedding the prions for some time.

So, as you can see, there are a few bugs to be worked out of this test, but it may be the welcome beginning of live animal testing for this prion disease. As yet, it is not commercially available or practical for deer farmers.

- Dr. Murray Woodbury, dvm wcvm