Creutzfeldt¨CJakob disease (CJD) in humans and bovine spongi
form encephalopathy (BSE) in cattle are invariably fatal, subacute degenerative diseases of
the brain that are classified as transmissible spongi
form encephalopathies. 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 o
ther infectious agents, elicit no demonstrable inflammatory or classic immune response. The most sensitive, specific, and generally available method
for confirming
these diseases is by pathologic examination of brain tissue.
As transmissible spongiform encephalopathies, CJD and BSE are regarded as the same type of disease process. The leading etiologic hypothesis for these diseases is that they result from the accumulation, in affected brains, of the transmissible agent, which consists of an abnormal form of a host-encoded glycoprotein. This transmissible agent was named a ¡°prion?in 1982.
Since CJD in humans was first reported in 1968 to be transmissible to chimpanzees, there has been continued speculation about the possibility of natural transmission of this disease to account for the over 85 % of CJD cases that seem to occur sporadically with no known source of infection. No natural route for transmission of CJD, however, has been convincingly demonstrated. Potential environmental risk factors, including consumption of various organ meats, have been examined in a number of case-control studies, but results have been conflicting. To explain the similar incidence of CJD (about one case per million population per year) found in many different geographic areas of the world and the absence of apparent environmental risk factors, prominent investigators have hypothesized that 85 % or more of CJD cases (i.e., those classified as sporadic, with no known environmental source of infection) result from de novo spontaneous generation of the self-replicating prion protein. Further, this process may be facilitated by an occasional somatic mutation that increases the usually rare stochastic fluctuations in the structure of the normal cellular precursor to the prion protein.
