Mad Cow Disease is related to both scrapie in sheep and bovine spongiform encephalopathy virus. The fear in Great Britain is the potential for acquiring Creutzfeldt-Jakob disease, which is a slowly progressive neurodegenerative disease. Theoretically, such acquisition could be through ingestion of beef from infected cows. A prion consists of protein material without nucleic acid. While related to a virus, a prion is a proteinaceous infectious particle that replicates within cells.