The tests turned up positive, they say, for abnormal prions, the infectious proteins believed to cause mad cow disease.

It is now known it is due to a type of infectious protein called a prion.

Mad cow disease, which is always fatal, is believed to be caused by an infectious protein called a prion.

But the agency said the woman was probably exposed to the infectious protein that causes the disease before she moved to Florida in 1992.

Many scientists believe the diseases are caused by prions, infectious proteins thought to cause brain damage.

And maybe infectious proteins had some way of making normal ones refold into the deadly con-formation.

The second is caused by a prion, an infectious protein that seems to "persuade" other proteins to imitate its abnormal folds.

If prevalence was the case, the infectious proteins would then have to cross the blood-testis barrier to make transmission possible.

This is due to a type of infectious protein called a prion.