Agent replication dynamics in a long incubation period model of mouse scrapie.

The dynamics of scrapie agent replication in brain and spleen following intracerebral or intraperitoneal infection were investigated in a model with particularly long incubation periods [IM mice (Sincp7) infected with 87V scrapie]. In contrast to other mouse scrapie models previously investigated, there was no delay in onset of replication ('zero phase') in spleen using either route of infection, For both routes infectivity levels reached a plateau in spleen, which was maintained for at least 250 days in intraperitoneally infected mice. An infectivity plateau was also apparent in brain following intracerebral infection, suggesting that there may be constraints on agent replication in brain during the later part of the incubation period. In addition, the efficiency of the intraperitoneal route to produce disease was found to be particularly low for this model.