Prion diseases: Boundaries with degenerative conditions of the nervous system

It is not possible to confirm the hypotheses which suggest that many diseases of the human nervous system are due to prions. Indeed, the large number of attempts to transmit degenerative diseases of known and unknown diagnosis to many animal species, and particularly to primates, have largely been unsuccessful. The rare transmission to inoculated animals have been attributed to laboratory contamination (1, 2). Prion diseases are very rare; the prevalence of Creutzfeldt-Jakob disease is 1/1,000,000 and that of other conditions even lower. As no peripheral marker is available, only a probable diagnosis can be made from the clinical examination and complementary examinations. The study of the nervous system by biopsy or autopsy is the only method permitting accurate diagnosis of encephalopathy due to sporadic prions, whether idiopathic or iatrogenic. No significant lesion has been demonstrated other than in tissue of the nervous system. Their mild infectious nature can lead us to fear irregular and delayed experimental transmission in animals. Pathology examination of the nervous system and the detection of abnormal PrP by Western blot give comparable results which permit confirmation of diagnosis. These simple and reliable techniques can provide results in a few days. They must be undertaken by trained staff because they involve infectious samples which resist traditional disinfection measures and must therefore be handled with particular care (3). It is necessary to maintain epidemiological surveillance.