| Prions in Humans | Prions in Domestic Animal Populations | Prions in Wild Animal Populations |
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Prions are proteinaceous infectious particles that are known to cause a group of fatal neurodegenerative disorders called “Transmissible spongiform encephalopathiers” (TSE) that attack the central nervous system, characterized by the spongy degeneration of the brain. In all cases these diseases are fatal and there are no treatments or vaccines. Examples of these diseases include Bovine spongiform encephalopathy (BSE), or "mad cow disease" which affects cattle, Scrapie, which affects sheep and goats and Chronic wasting disease, which affects cervids such as mule deer, white-tailed deer, and Rocky Mountain elk. In humans, Creutzfeldt-Jakob Disease (CJD) is a rare and fatal form of TSE that affects humans worldwide. A newly recognized form of CJD, called variant Creutzfeldt-Jakob disease (vCJD), has been diagnosed since 1996 and is thought to be linked to the consumption of meat products derived from BSE-infected cattle.
Prions are an abnormal form of glycoprotein located in cell membranes. Under normal conditions, the glycoproteins are sensitive to degradation by proteases and soluble. Although their function is unknown it is present in high concentrations in neurons and cells of the lymphoreticular system. The abnormal form, or prion, is identical to the normal glycoprotein in amino acid sequence, however, its three dimensional structure is different and it is partially resistance to degradation by proteases. Since the amino acid sequence of a prion is very similar or identical to that of the host they fail to stimulate an immune response.
Prions cause disease when they are ingested and taken up by cells of the lymphoreticular system in the gastrointestinal tract. The prion catalyses the conversion of normal protein into the abnormal form or prion. From there it is transferred to autonomic nerves that innervate the gastrointestinal tract and spreads to the central nervous system. It continues to catalyse the conversion of normal protein to abnormal protein, which accumulates in the central nervous system.