Several conditions fall under the term prion diseases. A prion is a type of protein that can trigger normal proteins in the brain to fold abnormally. Prion diseases can affect both humans and animals and are sometimes transmitted to humans by infected meat products.The most common form of prion disease that affects humans is Creutzfeldt-Jakob disease (CJD).his is an infectious type of the disease that is related to “mad cow disease.” Eating diseased meat may cause the disease in humans. The meat may cause normal human prion protein to develop abnormally.