MYSTERIOUS PROTEIN TRIGGERS MAD COW.(MAIN)

Byline: JOSEPH B. VERRENGIA Associated Press

Mad cow disease is caused by a mysterious rogue protein that is hard to trace and impossible to treat. With so many cases already established around the world, scientists say it was inevitable that it would show up in a herd in the United States.

While strict quarantines and food management might help protect consumers and cattle, there is no cure or vaccine to prevent the fatal infection. There are several research efforts under way, but a useful medicine or vaccine is probably years away.

Nor are there tests to detect it before an animal shows symptoms or to spot it in people who may have eaten tainted …