Currently, no proven test can detect BSE in live animals, but this is an area of significant research. Diagnostic testing for BSE relies on direct examination of brain tissue for abnormalities or assay for the presence of the abnormal form of prion protein (PrPsc). These diagnostic tests are only capable of detecting PrPsc in brain tissue of an infected animal if it is within a few months of the onset of clinical disease.9
When clinically suspect animals are found in the United States, the animals are euthanized, and a brain sample is taken and tested at a USDA-approved state veterinary diagnostic lab. BSE suspect cattle are not allowed into the food supply. All animals exhibiting signs of central nervous system disorders, including animals tested and found negative for rabies, are tested for BSE. Also tested is a representative sample of downer animals and dead animals. The BSE testing protocol calls for an initial rapid test called an Enzyme-Linked Immunosorbent Assay (ELISA).
If the ELISA test is inconclusive, samples are sent for confirmatory testing to the National Veterinary Services Laboratories (NVSL). An immunohistochemistry test is conducted at NVSL and, concurrently, an OIE-approved Western Blot/immunoblot test is conducted at the National Animal Disease Center (NADC). These tests are designed to detect the presence of BSE-specific abnormal prion protein in the brain tissue. A diagnosis of BSE will be made if either one of the two confirmatory tests results in a positive reaction.