Prion Diseases

About Prion Diseases

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.

Prion proteins as infectious agents

The infectious agent of prion diseases is not thought to be a bacterium, virus or parasite. Instead, it is believed by most scientists to be an abnormal form of the prion protein (PrP). The normal form of PrP (PrP^c) is present in all healthy humans and animals. However, in prion disease somehow one or a few PrP^c molecules are converted to an abnormal infectious form, or prion (proteinaceous infectious particle). The abnormal molecules can then convert more of an individual human's or animal's PrP^c molecules to the abnormal form, eventually causing a neurological disease. Under certain circumstances (such as invasive medical procedures, or exposure to BSE-contaminated food), prion diseases can therefore be transmitted, because in some circumstances contact with even tiny amounts of prion-contaminated material can initiate this process in a healthy individual.