Protein particles which can infect are called

Prions are misfolded proteins that can trigger normal proteins in the brain to fold abnormally. They are responsible for many fatal and transmissible neurodegenerative diseases in humans and many other animals. The most common form of prion disease that affects humans is Creutzfeldt-Jakob disease (CJD) and that affects cattle is bovine spongiform encephalopathy or mad cow disease.