Detection of PrPSc in subclinical BSE with the paraffin-embedded tissue (PET) blot

The appearance of a new variant of CJD (vCJD) in young patients has caused considerable public concern and there is evidence that this novel disease i s caused by the same agent as BSE. BSE is a prion disease that became epide mic in the UK, with a peak incidence in January 1993. New test systems shou ld aim to identify BSE-infected cattle early in the incubation period. We c ompared the established histological and immunohistochemical methods and th e Western blot method used by Prionics with the PET blot method that detect s prion PrPSc deposits in formalin-fixed and paraffin-embedded tissue. Inve stigating the obex region with the PET blot all BSE cases were detectable a nd no false positive cases occurred. From the Swiss culling program, five c linically healthy cattle out of 1761 were identified as incubating BSE. Wit h the PET blot method four of them showed the same PrPSc deposition pattern that was seen in clinical BSE, though less conspicuous. In one of the five cases, PrPSc was restricted to two brain stem nuclei, a pattern that was r eported to be the first manifestation of PrPSc deposits in the brain after peripheral infection and one that occurs after half of the incubation time. In this case, histology and Western blot were negative.