Creutzfeldt-Jakob disease (CJD) and Bovine spongiform encephalopathy (BSE) are caused by a(n) ____.

A) virus
B) bacterium
C) protozoan
D) fungus
E) prion

Prion

Infectious agents composed of protein in a misfolded form, which can cause rare, progressive neurodegenerative disorders by inducing abnormal folding of specific normal proteins in the brain.

Creutzfeldt-Jakob Disease

A rare, degenerative, invariably fatal brain disorder that affects about one in every one million people per year worldwide.

Bovine Spongiform Encephalopathy

A neurodegenerative disease in cattle that affects the brain and spinal cord, also known as Mad Cow Disease.