Define a prion. Discuss the change in shape of a protein due to a genetic mutation, from coiled to folded. Introduced that they were first observed in Sheep brain and cause damage to the Central Nervous System. Use diagrams to indicate that they form a spongiform encephalopathy in the sheep. Discuss the variant which was detected in cows causing Mad Cow Disease. Discuss in humans the sponge like appearance of the brain in Creutzfeldt-Jacobs Disease caused by uncoiled protein molecules. Relate how thousands of beef cattle were killed to prevent the spread of CJD to humans. Briefly discuss the HIV virus as a pandemic.