REFLECTIONS ON SCRAPIE AND RELATED DISORDERS, WITH CONSIDERATION OF THE POSSIBILITY OF A VIRAL ETIOLOGY

The transmissible spongiform encephalopathies of domesticated animals, scrapie in sheep and bovine spongiform encephalopathy (BSE), and tran smissible mink encephalopathy are more than a scientific curiosity; un der certain circumstances their impact on commercial activities can be calamitous. Knowledge of their causation and pathogenesis is still ru dimentary, but many consider than an unconventional agent, the prion ( a brain protein, PrP), that is not associated with nucleic acid is inv olved in both. Others believe that conventional viruses, which replica te by virtue of their nucleic acid-defined genes, are involved in the causation and progression of the encephalopathies but that technical p roblems have prevented their identification. Others postulate even mor e exotic causative agents. While this paper will particularly address the possibility of a viral aetiology for these diseases, it is also em phasized that our knowledge of the state of the immune system in anima ls with encephalopathy needs broadening. There are remarkable gaps in our knowledge of the histopathology of these diseases, particularly th e nature of the characteristic vacuoles. Much further work is needed o n the biochemical changes in the brain and the serum, particularly of the latter as it could lead to an additional means of recognizing clin ical cases without waiting for the animal to die with subsequent exami nation of the brain for characteristic lesions and the presence of pro tease-K-resistant PrP.