NEW VARIANT CREUTZFELDT-JAKOB-DISEASE AND BOVINE SPONGIFORM ENCEPHALOPATHY

Creutzfeldt-Jakob disease (CJD) in humans and bovine spongiform enceph alopathy (BSE) in cattle are invariably fatal, subacute degenerative d iseases of the brain that are classified as transmissible spongiform e ncephalopathies. They are both caused by ''unconventional'' filterable agents, which have long incubation periods that are usually measured in years. These agents have unusually high resistance to disinfection and, unlike other infectious agents, elicit no demonstrable inflammato ry or classic immune response. The most sensitive, specific, and gener ally available method for confirming these diseases is by pathologic e xamination of brain tissue.(13, 22) As transmissible spongiform enceph alopathies, CJD and BSE are regarded as the same type of disease proce ss. The leading etiologic hypothesis for these diseases is that they r esult from the accumulation, in affected brains, of the transmissible agent, which consists of an abnormal form of a host-encoded glycoprote in. This transmissible agent was named a ''prion'' in 1982.(23) Since CJD in humans was first reported in 1968 to be transmissible to chimpa nzees, there has been continued speculation about the possibility of n atural transmission of this disease to account for the over 85% of CJD cases that seem to occur sporadically with no known source of infecti on.(15) No natural route for transmission of CJD, however, has been co nvincingly demonstrated. Potential environmental risk factors, includi ng consumption of various organ meats, have been examined in a number of case-control studies, but results have been conflicting.(15, 25) To explain the similar incidence of CJD (about one case per million popu lation per year) found in many different geographic areas of the world and the absence of apparent environmental risk factors, prominent inv estigators have hypothesized that 85% or more of CJD cases (i.e., thos e classified as sporadic, with no known environmental source of infect ion) result from de novo spontaneous generation of the self-replicatin g prion protein. Further, this process may be facilitated by an occasi onal somatic mutation that increases the usually rare stochastic fluct uations in the structure of the normal cellular precursor to the prion protein.(13, 22)