Surveillance for bovine spongiform encephalopathy (BSE) in fallen stock in Japan is conducted with a commercial enzyme-linked immunosorbent assay (ELISA) for mass screening. Western blotting (WB) and immunohistochemistry performed for confirmation of the ELISA . All tests are based on detection of an abnormal isoform of prion protein (PrPSc) in brain tissues, which have sometimes deteriorated in fallen stock. To evaluate BSE surveillance procedures for fallen stock, we examined PrPSc detection from artificially deteriorated BSE-affected bovine brain tissues using the commercial ELISA kit and compared the results with those of WB. The optical density (OD) values of the ELISA decreased with advancing deterioration of the tissues, whereas no reduction of the signal for PrPSc was observed in WB, even when performed after 4 days of incubation at 37ºC. The progressive decrease of the OD values in the ELISA appear to be caused by a partial loss of the N-terminal moiety of PrPSc due to digestion by endogeneous and/or contaminated microbial enzymes, and by the presence of ELISA inhibitors that are generated in deteriorated tissues. These results suggest that WB is the most reliable test for fallen stock, especially for cattle brains within decaying carcasses.
(Prion Research Team, Prion Disease Research Center TEL +81-29-838-7757)
References:
Hayashi et al. (2004) J. Vet. Med. Sci. 66:515-520.
