How it's contracted

Caused by a protein called a prion. A prion causes normal proteins to fold abnormally. This affects other proteins' ability to function. CJD is very rare. It occurs in about 1 out of every 1 million people.

In some cases, CJD has spread to other people from grafts of dura mater (a tissue that covers the brain), transplanted corneas, implantation of inadequately sterilized electrodes in the brain, and injections of contaminated pituitary growth hormone derived from human pituitary glands taken from cadavers.