Up to 30,000 Brits may be human carriers of mad cow disease. Here's what you need to know about bovine spongiform encephalopathy, or BSE.
What are the odds? -- The Centers for Disease Control and Prevention says the chance of humans contracting mad cow disease is less than one in 10 billion. Since 1996, 195 cases in 11 countries have been reported -- including two in the U.S.