Scrapie Diagnosis
Information about how the disease is diagnosed.
Scrapie should be diagnosed by a veterinarian as other diseases could mimic the signs and symptoms. The diagnosis is made by three variables:
- Clinical signs
- Live animal test - 3rd eyelid test
- Definitive diagnosing based on post mortem examination of selected sites from brain
On the farm, veterinarians diagnose scrapie based on the appearance of its signs combined with knowledge of the animal's history.
Scrapie can be diagnosed in the live animal by biopsy of the lymphoid tissues on the inside of the third eyelid.This test is used by the U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) to determine whether exposed flocks are infected. Unfortunately, the current third eyelid test is not fool-proof. A negative live-animal test does not confirm the animal is free of the disease. Not all "scrapie positive" animals accumulate enough prion on the eyelid to elicit a positive test. As a result, a positive test confirms infection, but a negative test result does not confirm an animal is scrapie free.
Scrapie is most often diagnosed by microscopic examinations of brain tissue at necropsy or by procedures that detect the presence of the abnormal prion protein in brain tissue.
As there is no treatment, death is inevitable within one to six months after the onset of clinical signs. External parasites, listeriosis, pregnancy toxemia, plant poisoning, OPP, lead poisoning, rabies, pseudorabies and brain abscesses may all display similar clinical signs. Therefore, a diagnosis of scrapie based on clinical signs must be confirmed by microscopic examination of brain tissue and/or by immunohistochemistry which tests for the presence of the prion protein.
