Those who have the disease tend to experience a progressive neurological or psychiatric disorder that lasts longer than six months with symptoms including dementia, seizure, unusual sensory symptoms, dizziness, or progressive unusual mood changes. The illness usually lasts 14 months, and the disease is always fatal.
As of last year, 221 cases of probable vCJD had been reported. This includes 172 in the United Kingdom, 25 in France, five in Spain, four in Ireland and three in the United States, with a smattering of cases in other countries around the world. The patients that were diagnosed in the United States were thought to have been infected while they were residing in the UK or living abroad in Saudi Arabia.
No humans have ever been reported to have been infected with mad cow disease in the United States, but fears of the disease became prominent in the 1990s when nearly 150 people in Britain died from the brain-wasting disease.
ABC News' Dr. Christopher Tokin contributed to this report.