1. Prion Research Unit, Department of Medicine, School of Medicine, University of Santiago de Compostela, Rue de S. Francisco s/n, Santiago de Compostela, Galiza, Spain 15782, Western Regional Research Center, United States Department of Agriculture, Room 3124, 800 Buchanan Street, Albany, California 94710, and Department of Neurology, University of Texas Medical Branch, 301 University Boulevard, Galveston, Texas 77555