Prion Diseases in Animals

Abstract

Prion diseases refer to a group of invariably neurodegenerative diseases in humans and animals, collectively known as transmissible spongiform encephalopathies (TSEs). These diseases are caused by proteinaceous infectious particles that lack nucleic acid, called prions. This paper reviews prion diseases occurring in animals, excluding human spongiform encephalopathies.

Prions in animals include scrapie or ovine spongiform encephalopathy, bovine spongiform encephalopathy (BSE), transmissible mink encephalopathy (TME), chronic wasting disease (CWD) of mule deer and elk, and feline spongiform encephalopathy (FSE). These diseases share several characteristics: a long incubation period (ranging from months to years or even decades), a clinical course lasting from weeks to years that invariably ends in death, lesions largely restricted to the central nervous system, and a lack of immune response. Histopathological changes include neuronal degeneration with vacuolation (spongiform degeneration), reactive astrocytosis, and often “amyloid plaque” formation. Variations exist among these diseases concerning incidence, breed and species susceptibility, and incubation time.

While extensive information is available for scrapie and BSE, data on other animal spongiform encephalopathies remain limited. This paper discusses the occurrence, host range, clinical signs, histopathology, transmission, and diagnosis of these diseases, with a particular focus on scrapie and BSE. It is suggested that BSE resulted from cattle ingesting meat and bone meal from scrapie-infected sheep, and TME is considered to have originated similarly. Bovine-to-bovine transmission has been linked to feeding cattle with bovine-derived meat and bone meal. Consequently, the ban on using ruminant-derived meat and bone meal has significantly reduced the incidence of BSE.

There is no direct evidence that animal spongiform encephalopathies are transmissible to humans. However, cases of a new variant of Creutzfeldt-Jakob Disease (vCJD) in teenagers and young adults in Britain and France revealed distinct neurological lesions not observed in classical CJD cases in adults from the United States, Australia, or Japan. These lesions, characterized by numerous amyloid plaques, are similar to those found in macaques inoculated with bovine prions.
None of the transmissible spongiform encephalopathies discussed in this paper have been reported in the Philippines

Keywords