Proteins expressed from within the prion protein genes of all animals and humans, "prionins", against which reagents can be prepared for accurate pre-symptomatic diagnosis, for detecting latent TSE, for detecting TSE contamination of food, blood and blood products and for therapeutic treatment of Bovine spongiform encephalopathy (BSE) in cows, Scrapie disease in sheep and Creutzfeldt-Jacob syndrome in humans, are revealed.