Prion diseases are rare, fatal, degenerative brain disorders that are thought to occur worldwide in both humans and animals. They belong to the general category of brain diseases called proteinopathies, which also includes Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis (ALS). Although there are several forms of human prion disease, the most common is Creutzfeldt-Jakob disease (CJD). The term CJD is often used to refer to all forms of human prion disease. Prion diseases that affect animals include Bovine Spongiform Encephalopathy (BSE) in cattle, scrapie in sheep and goats, and Chronic Wasting Disease (CWD) in deer, moose, elk, and caribou or reindeer. Although they are rare, these diseases have caused great public health concern because of their many difficult and unusual features.
How Prion Diseases affect the brain
The brains of people or animals with prion disease undergo damage, called "spongiform change" or "spongiosis" because when the tissue is examined under a microscope it resembles a sponge, with many tiny holes. In addition, the brain tissue contains abnormal deposits of a specific protein called the prion protein (PrP). These pathological changes can be caused by genetic variations, or apparently arise spontaneously within a single individual. However, they can also be caused by infectious transmission between individuals of the same or different species.