Classic Slow Virus Dlseases1

The designation slow virus disease refers not to the causal agent but to the fact that the diseases induced have a slow, relentlessly progressive course and a fatal termination. These diseases can be divided into two categories according to whether the causal agent is a typical, conventional virus (propagable in vitro; cytopathogenic; antigenie; associated with inflammatory lesions, for example of the central nervous system, etc.) or a transmissible agent whose properties and behavior suggest an unconventional or atypical virus. In the latter category are four of the classic slow virus diseases, namely kuru and Creutzfeldt-Jakob disease of man (Table 1) and scrapie and mink encephalopathy of animals (Table 2). The transmissible agents involved are regarded as atypical viruses because of their nature, properties, and characteristics; and, because of the similar pathologic picture they induce, they are regarded as prototypic viruses of this group, collectively referred to as the subacute spongifoorm encephalopathies. The label encephalopathy rather than encephalitis is used because the widespread destructive cerebral changes present a pic-