Prion disease, TSE's are called spongiform encephalopathies, existing in both animals and humans. In the 1730's scrappie was the first of these diseases to be discovered. Associated with the build up in the brain of normal proteins. Once they begin forming they multiply and convert normal proteins into abnormal proteins. Normal prion proteins are used in the brain and then broke down and new ones are created but, abnormal proteins are resistant tot he process. Accumulating and causing damage to the brain. Not a contagious disease although it can be transmitted through infected tissues.