Diseases such as BSE (Bovine Spongiform Encephalopathy,“mad cow”), scrapie, Creutzfeldt-Jakob Disease (CJD) and Chronic Wasting Disease (CWD) are a family of fatal neurodegenerative disorders. These diseases can present with infectious, sporadic, or familial manifestation. They affect a number of mammals including cattle, humans, sheep, goats, mink, elk, deer and domestic cats. In the Canadian context, infectious spread of BSE has been both a concern and a catalyst for new research activity. Click here to find the current status of BSE tracking in Canada.
Prion diseases are also referred to as TSEs (Transmissible Spongiform Encephalopathies). They are frequently characterized by a spongy appearance, “spongiform” change, in the brain of affected animals or humans. This change is often (but not always) accompanied by clusters of aggregated proteins outside the brain cells: these clusters are referred to as amyloid deposits.
Prion diseases are not to be confused with viral infections. Highly infectious prion preparations do not contain virus-like structures, nor can genomic nucleic acids be detected within such preparations. Instead many lines of evidence indicate that in the disease process a benign, host-encoded α-helical protein (PrPC) undergoes a change in shape to a protease-resistant, β-sheet enriched and infectivity-associated form denoted PrPSc. In strong support of these ideas, subtle mutations in the mouse PrP gene (Prnp) impact disease progress and pathology, with complete removal of the mouse Prnp gene rendering animals completely resistant to infection.
In very rare circumstances, prion infections may be inadvertently caused by clinical procedures, a process referred to as iatrogenic disease. An example here would include iatrogenic CJD caused by administration of prion-contaminated growth hormone. Prion infections can be started in a laboratory setting by inoculating brain homogenate from affected animals into a recipient (experimental prion disease). In familial prion diseases of humans, certain dominant mutations in the human PRNP gene lead to a range of pathologies in the brain, with some closely resembling those of experimental prion infections.