Chronic Wasting Disease (CWD) is a degenerative
brain disease of deer and elk associated with a unique abnormal protein
agent. Testing for CWD involves examination of the brain for signs of
degeneration or testing of brain or lymph nodes for the presence of
the CWD agent associated with the disease.
The CWD agent develops slowly in an exposed animal, therefore the CWD
agent is impossible to detect early in the course of the disease. As
the disease progresses, the CWD agent accumulates in the brain and lymphatic
tissues like lymph nodes. No CWD agent has ever been found in muscle
meat, even from clinically-ill animals. Testing for CWD involves examination
of brain tissue, because that's where the agent is most likely to be
found in an affected animal.
CWD is difficult to diagnose. The brain of a CWD-affected deer or elk
looks normal to the naked eye. Even under the microscope, diagnosing
the disease can be difficult. Minnesota is using a special test called
immunohistochemistry (IHC) for detection of the CWD agent in brain samples.
The IHC test involves treating brain samples with special chemicals
and stains that bind to the CWD agent. Treated brain samples then are
examined under the microscope for evidence of the stained CWD agent.
Three different results may result from the testing:
- A POSITIVE
test result means that the CWD agent was identified in the brain tissue.
All of these tests will be confirmed by the United States Department
of Agriculture National Veterinary Services Laboratory.
- A NEGATIVE
test result means that the no CWD agent was detected in the brain
sample examined. However, if the deer or elk was recently exposed,
it is possible that the CWD agent is present at very low levels that
cannot be detected.
- No test
results will be available from a small number of brain samples that
prove to be UNSUITABLE FOR TESTING. The brain tissue degenerates rapidly
after an animal dies. Trauma to the brain during hunting, handling
of the tissue, or high temperatures may damage the tissue so much
that the test cannot be performed.
The CWD testing process is very labor intensive, taking almost a week
under the best circumstances. Currently the diagnostic laboratory can
handle only a limited number of tests each day. Therefore, if large
numbers of samples are received, test results may be delayed for several
weeks to several months.
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