ABSTRACT

It is well established that the prion infectious agent, like conventional microorganisms, exhibits strain variation and species barrier. Diverse prion strains have been identified in mice, hamsters, sheep, cattle, and humans. Strains differ on disease characteristics, including incubation period, neuropathology, and clinical symptoms. In addition, prions from one animal species can infect only a limited number of other animal species. Understanding how a single protein can provide the diversity to sustain the variety of strains and the species-barrier phenomenon has been a challenge for the prion hypothesis [Prusiner, 1998; Soto and Castilla, 2004]. This chapter reviews the characteristics of prion strains and the species-barrier process and discusses the evidence indicating that the prion protein (PrP) structure enciphers these phenomena.