II. Prion Diseases in Man and Animals

To date, a total of 13 prion diseases have been recognized in man and animals. The human diseases are: Kuru, Creutzfeldt-Jakob disease (CJD), variant CJD, Gertmann-Straussler-Scheinker Syndrome, fatal familial insomnia and Alpers’ disease. The animal diseases are: scrapie, transmissible mink encephalopathy, chronic wasting disease, bovine spongiform encephalopathy, feline spongiform encephalopathy, wild ungulates encephalopathy and spongiform encephalopathy of the ostrich. Early diagnosis and treatment of these diseases have bewildered the scientific community. The fact that the prion protein (PrP) is derived from the host – given that PrP is the sole cause of disease makes it almost impossible to develop direct serologic tests and vaccines for the diagnosis and prevention of these diseases. At present, diagnosis is largely based on clinical and postmortem findings, detection of abnormal prion protein by immunocytochemistry, Western blot, infra-red spectroscopy and biochemical examination of cerebraospinal fluid and blood of suspected patients. Methods are currently being evaluated for the identification of “capture” agents that specifically bind to misfolded prion protein (PrP), and for amplification of the interconversion of normal prion protein into PrP. No treatment is available yet for prion diseases, but several candidate drugs are being investigated that could prevent PrP formation, interfere with its conversion and/or metabolism or reverse it into the normally folded, harmless form. Introduction: During the past few years, considerable advances have been made towards better understanding of prion diseases and the development of new methods for their diagnosis and treatment. In part I of this review, we have described the etiology of these diseases, and the hypothesis that have been put forth to explain their nature and propagation. In the second part of the review, the clinical manifestations, pathogenesis, diagnosis and treatment of different types of prion disease affecting man and animals will be described. II. Prion Diseases in Man and Animals Mansour F. Hussein & Saud I. Al-Mufarrej 140 Prion diseases, or transmissible spongiform encephalopathies (TSE) are peculiar, neurodegenerative disorders that are apparently caused by a misfolded "infectious" prion protein, hitherto known as PrP or PrP. These diseases are unique in that they are both infectious and inherited. All of them are characterized by a long incubation period, followed by progressive spongiform degeneration of brain tissue, with consequent dementia, motor disorders, paralysis and 100% mortality [2]. The primary lesions comprise neuronal vacuolations and loss, especially in the cerebellum and cortical parts of the brain stem. These changes are accompanied by extensive gliosis, astrocytosis [3] and accumulation of abnormal prion protein fibrils in and around the brain cells [4]. To date, thirteen types of prion diseases have been described in humans and different species of domestic and wild animals (Table 1). Table ( 1 ) Human and Animal Prion Diseases