Peripheral pathogenesis of prion diseases

Prions are infectious pathogens that cause a group of neurodegenerative dis eases characterized by spongiform degeneration of the central nervous syste m. Prions appear to lack any informational nucleic acid. The most notable p rion diseases include bovine spongiform encephalopathy, scrapie in sheep an d Creutzfeldt-Jakob disease of humans. Transmission is thought to be achiev ed through conversion of a normal host protein into a pathological isoform. Although the main pathological changes during the course of the disease oc cur in the brain, the infectious agent accumulates early in lymphoid tissue . The subsequent development of clinical disease depends on the presence of an intact immune system including mature B-cells. In this article we revie w the state of knowledge on the routes of neuroinvasion used by the infecti ous agent in order to gain access to the central nervous system upon entry into extracerebral sites. (C) 2000 Editions scientifiques et medicales Else vier SAS.