FIG 1.

Origins of the various TSE-positive isolates used within this study (naturally acquired or generated). The top line represents the three “natural” TSE agent types that we started from (natural scrapie from either VRQ/VRQ ([n = 3] or ARQ/ARQ [n = 3] sheep or cattle BSE [n = 3]). Their respective expected incubation times under natural conditions are specified in years. For cow BSE and BSE-derived isolates, several experimental passages to cattle and sheep (either ARQ/ARQ or VRQ/VRQ) have been performed by various transmission routes (intracerebral or oral). Their averaged incubation times are given in days (±standard deviation) after inoculation until clinical disease. Data for oral transmission of cow BSE to ARQ/ARQ sheep are from Thuring et al. (53). Other transmissions are new (L. J. M. van Keulen, unpublished data).