Variant Creutzfeldt-Jakob disease (vCJD) is a degenerative, fatal brain disorder in humans. Symptoms are initially psychiatric or sensory and include neurological abnormalities such as ataxia, dementia, and myoclonus. There is no known treatment for vCJD.
Mad cow disease (or bovine spongiform encephalopathy [BSE]) is a fatal disease that attacks the central nervous system of adult cattle. Though the specific cause isn't known, it is speculated that infectious prions are the likely cause. Creutzfeldt-Jacob disease is found in people and is similar to BSE. A variation of this disease is thought to be caused by eating beef products from BSE-infected cattle.