Abstract
Prions are transmissible agents that comprised of a misfolded protein PrPSc that is posttranslationally derived from the normal isoform PrPC. Prion strains are operationally de fi ned by differences in the distribution and intensity of spongiform degeneration and distribution of PrPSc in the CNS. The mechanism by which prion strains are encoded is not known; however, current evidence suggests that the conformation of PrPSc encodes prion strain diversity. In natural prion disease, more than one prion strain can exist in an individual. Prion strains, when present in the same host, can interfere with each other, a process that may be important during prion adaptation following interspecies transmission. While the parameters that in fl uence prion strain interference are beginning to be described, the mechanism responsible for strain interference is not known.