Prion diseases

Abstract

Prion diseases are invariably fatal neurodegenerative diseases of humans and animals that attracted worldwide attention after detection of a bovine spongiform encephalopathy outbreak and its transmission to humans causing variant Creutzfeldt-Jakob disease. Prion diseases are unique among infectious diseases because of the unconventional characteristics of the etiologic agent and the biochemical mechanism for its propagation and because of the sporadic, genetic, and transmissible nature of some of these diseases. The agent causing prion diseases, termed prion, is an abnormal conformer of a host-encoded cellular protein known as the prion protein. The seminal event in the occurrence of prion diseases appears to be conversion of the cellular prion protein to the pathogenic prion by a poorly understood posttranslational process. Transmission of prion diseases within the same species has been extensively documented in sheep, cows, cervids, and humans. The modes of such transmissions include consumption of contaminated feed, accidental inoculation via medical or veterinary interventions, close animal-to-animal contact, and transmission via environmental contamination. Depending on the host species, these transmissions result from exposures to secretions or tissues known to harbor the infectious agent, including the brain, spinal cord, lymphatic tissues, saliva, and blood. Although cross-species spread of animal prion diseases has long been suspected, strong evidence for such spread is only available for the transmission of bovine spongiform encephalopathy to humans, domestic cats, and zoo animals.