PATHOGENS

• Prions are abnormally folded versions of cell membrane proteins otherwise normally found throughout the human body.
  • Abnormal versions are resistant to most types of proteolytic degradation, including resistance to many chemicals and physical methods of inactivation.
  • The origin of initial conversion to the abnormal version is unclear but, once present, can induce the conversion of nearby proteins from the normal cellular prion protein (PrP^C) form to the abnormal and infective prion scrapie (PrP^Sc) form.
  • Normal PrP^C and abnormal PrP^Sc forms share identical protein primary structures, so the abnormal PrP^Sc does not seem to trigger an immune response.
  • Normal PrP^C plays an important role in the organogenesis and development of the central nervous system; it also affects the pathogenesis of neurodegenerative diseases and cancers
• Prions cause transmissible spongiform encephalopathies (TSEs).
• Epidemiology: Annual incidence is about 1.2 cases per million people in the U.S.; it increases with age.