This research was published online as early as OCTOBER 21. One is led to wonder why the broadsheets chose this weekend to publicise Prof Prusiner's conjecture that muscle and flesh of cattle and sheep may harbour deadly levels of prions that cause variant CJD.
 
 
 Technical Reports
 
Published online: 21 October 2002, doi:10.1038/nbt748
November 2002 Volume 20 Number 11 pp 1147 - 1150

Measuring prions causing bovine spongiform encephalopathy or chronic wasting disease by immunoassays and transgenic mice
Jiri G. Safar1, 2, Michael Scott1, 2, Jeff Monaghan1, 5, Camille Deering1, Svetlana Didorenko1, Julie Vergara1, Haydn Ball1, Giuseppe Legname1, 2, Estelle Leclerc4, Laura Solforosi4, Hana Serban1, Darlene Groth1, Dennis R. Burton4, Stanley B. Prusiner1, 2, 3 & R. Anthony Williamson4
 
1. Institute for Neurodegenerative Diseases, University of California, San Francisco, CA 94143-0518.
2. Department of Neurology, University of California, San Francisco, CA 94143-0518.
3. Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94143-0518.
4. Departments of Immunology and Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037.
5. Current address: InPro Biotechnology, 870 Dubuque Avenue, South San Francisco, CA 94080.
Correspondence should be addressed to S B Prusiner. e-mail: stanley@itsa.ucsf.edu and D R Burton. e-mail: burton@scripps.edu

There is increasing concern over the extent to which bovine spongiform encephalopathy (BSE) prions have been transmitted to humans, as a result of the rising number of variant Creutzfeldt–Jakob disease (vCJD) cases. Toward preventing new transmissions, diagnostic tests for prions in livestock have been developed using the conformation-dependent immunoassay (CDI), which simultaneously measures specific antibody binding to denatured and native forms of the prion protein (PrP). We employed high-affinity recombinant antibody fragments (recFab) reacting with residues 95–105 of bovine (Bo) PrP for detection and another recFab that recognizes residues 132–156 for capture in the CDI. We report that the CDI is capable of measuring the disease-causing PrP isoform (PrPSc) in bovine brainstems with a sensitivity similar to that of end-point titrations in transgenic (Tg) mice expressing BoPrP. Prion titers were 107 ID50 units per gram of bovine brainstem when measured in Tg(BoPrP) mice, a figure 10 times greater than that determined by bioassay in cattle and 10,000times greater than in wild-type mice. We also report substantial differences in BoPrPSc levels in different areas of the obex region, where neuropathology has been consistently observed in cattle with BSE. The CDI was able to discriminate between PrPSc from BSE-infected cattle and Tg(BoPrP) mice as well as from chronic wasting disease (CWD)-infected deer and elk. Our findings argue that applying the CDI to livestock should considerably reduce human exposure to animal prions.