Mad cow disease is a rare illness people can get from eating infected beef.It is a fatal,neurodegenerative disease in cattle, that causes a spongy degeneration in the brain and spinal cord. In humans, the symptoms include insomnia, depression, confusion, personality and behavioral changes, and problems with memory, coordination, and sight. In later stages, the person rapidly develops dementia and involuntary, irregular jerking movements called myoclonus.