ABSTRACT
CONTENTS 4.1 Transmissible Spongiform Encephalopathies ........................................ 66
4.1.1 TSE Agents, Prion Proteins, and Disease Pathogenesis ........... 68 4.1.2 Transmission of TSEs ..................................................................... 69 4.1.3 TSE Agent Strains ........................................................................... 70 4.1.4 Pathogenesis of TSEs...................................................................... 71 4.1.5 TSE Testing ...................................................................................... 71
4.2 Bovine Spongiform Encephalopathy ....................................................... 72 4.2.1 Origin of BSE ................................................................................... 73 4.2.2 Distribution of Infectivity in Tissues of Cattle
after Infection with BSE Agent ..................................................... 74 4.2.3 Age of Cattle and Clinical Disease .............................................. 81 4.2.4 Slaughter Techniques and Potential for Contamination
of Meat with BSE Agent ................................................................ 82 4.2.5 BSE in Species Other Than Cattle ................................................ 82 4.2.6 Creutzfeldt-Jakob Disease, Variant Creutzfeldt-Jakob
Disease, and Other TSEs of Humans .......................................... 83 4.2.7 BSE Agent in the Food Supply..................................................... 85
4.2.7.1 International Recommendations on BSE ..................... 85 4.2.7.2 National Requirements for BSE
in the Food Supply .......................................................... 89 4.3 Scrapie........................................................................................................... 90
4.3.1 Transmission of Scrapie................................................................. 91 4.3.2 Distribution of Infectivity in Sheep and Goats with Scrapie... 92 4.3.3 Scrapie Agent in the Food Supply............................................... 92
4.4 Chronic Wasting Disease........................................................................... 92 4.4.1 Transmission of CWD.................................................................... 94 4.4.2 Distribution of Infectivity in Cervids with CWD...................... 95 4.4.3 CWD Agent in the Food Supply .................................................. 96
4.5 Conclusion ................................................................................................... 97 References ............................................................................................................. 97
During the past two decades, transmissible spongiform encephalopathies (TSEs or prion diseases) have garnered a great deal of attention due to the recognition, in 1986, of a new TSE called ‘‘mad cow disease’’ (known scientifically as bovine spongiform encephalopathy or BSE). The spread of BSE to cattle in at least 26 countries and the subsequent realization that BSE has been transmitted to humans had a great impact on food safety policy and affected international trade worldwide. When discussing food safety related to TSEs, we are mainly concerned with products from those ruminants widely used for food in North America: cattle, sheep, and, to a lesser extent, cervids. This chapter begins by discussing TSEs in general and then focuses on TSEs in the animals of interest and, especially, on measures to reduce the risk of TSE agents entering the food supply.
