Transmissible spongiform encephalopathies (TSEs), or prion diseases, are a group of neurodegenerative diseases affecting both animals and humans. Among the more commonly known TSEs are scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle, chronic wasting disease (CWD) in deer and elk, and Creutzfeldt-Jakob disease (CJD) in people. Other ungulates, mink, and felids can also be affected, and a variety of additional prion diseases have been described in people (table 1).

     table1    figure1
Despite the wide range of host species, prion diseases manifest with similar histopathological changes. The accumulation in the brain of an aberrantly folded form of what is thought to be the etiological agent – the prion protein (PrP) – is a pathognomonic finding (2). In addition, vacuolar (spongiform) degeneration of the central grey matter, neuronal loss and astrocytosis are hallmark features (figure 1). The degree of expression of these features varies between diseases, as does the presence or absence of amyloid plaques. For example, diseases such as scrapie, BSE, kuru, sCJD, iCJD, fCJD, fFI, and sFI are characterized by vacuolar changes in the cerebral grey matter without substantial amyloid plaque formation. In contrast, cases of GSS present with little spongiform degeneration but substantial deposition of PrP-positive amyloid plaques. vCJD presents differently again, with both vacuolar changes and amyloid plaques (4).



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