1.   The misfolded prions accumulate into toxic clumps that eventually destroy normal brain tissue.

2.   These misfolded prions accumulate in toxic clumps, eventually destroying normal brain tissue and creating spongelike holes.

3.   Transmission is difficult to track, however, because people or animals typically develop the disease a long time after they have been exposed to the misfolded prions.

4.   When a misfolded prion comes into contact with a healthy prion, he said, it can sometimes force the normal prion to change shape.