Prion diseases -- incurable, ultimately fatal, transmissible neurodegenerative disorders of mammals -- are believed to develop undetected in the brain over several years from infectious prion protein. In a new study, NIH scientists report they can detect infectious prion protein in mouse brains within a week of inoculation. Equally surprising, the protein was generated outside blood vessels in a place in the brain where scientists believe drug treatment could be targeted to prevent disease.