Pathogenesis of Scrapie: Agent Multiplication in Brain at the First and Second Passage of Hamster Scrapie in Mice

Abstract

The intracerebral (i.c.) injection of mice with a particular source of hamster passaged scrapie produced disease after an incubation period of 325 ± 6 days (mean ± s.e.). The incubation period at the second i.c. passage in mice was reduced to 149 ± 2 days. Studies were made of the dynamics of agent replication at 1st and 2nd passages in mice. At first passage, there was a ‘zero phase’ lasting about 175 days, when no infectious agent was detected in brain (or spleen), followed by a period of agent replication which lasted 150 days. At second passage, there was no significant ‘zero phase’ and agent replication occupied the whole of the incubation period. The occurrence of a ‘zero phase’ on interspecies passage of scrapie is discussed in relation to other reports of a ‘zero phase’ in mouse passaged scrapie.