4 Transmission and Replication of Prions

Abstract

One of the most remarkable features of slow infections is the clockwork precision with which the replication of prions occurs. Inoculation of numerous animals with the same dose of prions results in illness at the same time months later. The molecular mechanisms controlling this extraordinarily precise process are unknown.

The term infection implies that a pathogen replicates during this process. When the infectious pathogen has achieved a high titer, a disease in the host often appears. Prior to the recognition of the existence of prions, all infectious pathogens contained a nucleic acid genome that encoded their progeny. Copying of this genome by a polynucleotide polymerase provided a means of replicating the pathogen; in the case of prions, another mechanism functions.

GENERAL FEATURES OF PRION TRANSMISSION AND REPLICATION
As we learn more about prions, some general features and rules of prion replication are beginning to emerge. Although many of the results described here can be found in other chapters, we felt that it was important to collect information on prion transmission and replication in one place within this monograph.

Prion Replication and Incubation Times
When the titer of prions reaches a critical threshold level, the animals develop signs of neurologic dysfunction. The length of the interval from inoculation to reach the threshold prion concentration, at which CNS dysfunction becomes evident, is referred to as the incubation time or incubation period.

The length of the incubation time can be modified by (1) the dose of prions, (2) the route of inoculation, (3)...