APHIS Factsheet

Animal and Plant Health Inspection Service April 2012

Western Blot Similarities/Differences BSE • Several types, with the SAF • Both IHC and the Immunblot Immunoblot and commercially (Western blot) are Confirmatory available Western blot kits internationally recognized as recognized by OIE. confirmatory tests for BSE. Tests • Used under USDA protocol • The tests use different when a sample is “not suitable methods to determine if the Immunohistochemistry (IHC) for IHC”, i.e., if it is autolyzed abnormal prion protein is • Primary confirmatory test (or degraded) or brain stem present in brain tissue of an for USDA’s BSE surveillance architecture is not evident animal. program. microscopically. • The IHC test additionally • Recognized by the World • Uses a large portion of obex allows for the viewing of brain Organization for Animal Health, brain tissue; the abnormal tissue to determine if lesions or OIE. prion protein in brain material characteristic to BSE are • Allows scientists to determine is enriched, and the sample present. if a sample is positive for BSE is exposed to protease, an • Both tests are equally in two distinct ways: visually enzyme, to destroy any normal effective at detecting the (spongiform changes), and prion proteins that may be classical form of BSE. through a staining technique present, leaving only abnormal (presence of abnormal prion prion proteins. Remaining protein). sample is then run through a • Involves looking at an intact gel to separate the abnormal portion of the brain, the obex, to prion protein components USDA is an equal opportunity provider see if there are lesions (holes or by molecular weight. After and employer. a “spongy” appearance) present the transfer of the proteins that are characteristic for BSE, to a membrane, proteins and using a staining process are stained using antibodies using antibodies that detect the that can identify a specific abnormal protein prion. banding pattern associated • Takes four to seven days to run. with prion diseases including • Freezing samples does not BSE. A diagnosis is made by interfere with performing the IHC recognizing three distinctive test as long as the sample is bands that are identified as confirmed as obex. a result of a reaction with the anti-prion protein antibody. • Freezing samples does not interfere with the performance of western blot tests.

United States Department of Agriculture • Animal and Plant Health Inspection Service • Safeguarding American Agriculture