Creutzfeldt-Jakob disease (CJD) is a rare, rapidly progressive viral disease that attacks the central nervous system, causing dementia and neurologic signs and symptoms, such as myoclonic jerking, ataxia, aphasia, visual disturbances, and paralysis. It generally affects adults ages 40 to 65 and occurs in more than 50 countries. Males and females are affected equally. CJD is always fatal. A new variant of CJD (nvCJD) emerged in Europe in 1996. (See Understanding nvCJD.)