Pathogenesis of classical and atypical BSE in cattle.

It is known from earlier studies that the pathogenesis of BSE in cattle differs considerably from the TSE pathogenesis in sheep, where the lymphoreticular system (LRS) is majorly involved in the transport and propagation of the agent. In cattle, the BSE agent has only been detected in the Peyer's patches of the distal ileum and in the tonsils, which have both been identified as the portal of entry for the agent after oral uptake. It was shown that as opposed to most other animal species, in cattle the BSE agent amplifies almost exclusively in the central and peripheral nervous system. However, there is growing evidence for a centrifugal spread from the central nervous system into the periphery at the late stage of the disease. Moreover, there are only very limited data available concerning the pathogenesis of both atypical BSE forms, H type and L type BSE, as compared to classical BSE. In this manuscript we summarize the most recent data that we generated on the classical BSE pathogenesis after an oral challenge study that was performed with 56 cattle. Preliminary results on the pathogenesis of both atypical BSE forms are also presented, based on an intracranial challenge of cattle with German isolates of both atypical BSE forms.