Probability, Luck and One Mad Cow:
"IN recent years, the Department of Agriculture has been warned numerous times that its testing system was not going to be able to stop mad cow disease from getting into American beef.

And if the disease was already in the United States - which it was, since a cow that was probably infected shortly after birth four and a half years ago has now been found with it - the chances of spotting it quickly were low."

In fact, the lone case was caught largely by luck. It involved a "downer" cow - that is one unable to walk. Though the inability to walk can be a symptom of mad cow disease, in this case it was attributed to her having ruptured while giving birth. In the end, it was not clear why the animal's brain was sent to the department's lab in Ames, Iowa.

But it was clear, several experts say, that the United States was vulnerable to mad cow disease. Dr. Stanley Prusiner, who won the 1997 Nobel Prize in Medicine for his work on prions, the misfolded proteins that cause the disease, said that six weeks ago he met with Ann M. Veneman, the secretary of agriculture, and warned her that the country was vulnerable to an outbreak.

The 1997 book "Mad Cow U.S.A.," by Sheldon Rampton and John C. Stauber, made the case that the disease could enter the United States from Europe in contaminated feed.

Since 1997, Consumers Union, which publishes Consumer Reports, has sent numerous letters to Agriculture Department officials warning that the American testing was "flawed in both design and execution," and that native brain disease, not necessarily caused by feed imported from Britain in the 1980's, "may be hiding among the 'downer cow' population."

It also warned that studies suggested that some pigs suffered from encephalopathy, particularly dangerous because it is still legal to feed rendered pigs - pig parts boiled, ground and dried into a powder - to cows.…

http://www.nytimes.com/2003/12/28/weekinreview/28madd.html