Can protein infect another protein?

Very strange, but Yes. These are called prion proteins. They are not necessarily living organisms, but they can spread and can be contagious.

So what are they?

Well, In general, protein is a large molecule that is folded on itself. This folding gives them a specific function.

Rarely a production error can make a protein that has the function of folding other proteins into its own shape. So you can see here it starts a chain reaction and spreads throughout the body.

Creuztfeld Jakob disease (CJD) is a rare brain disease that occurs from these prion proteins. As this protein spreads in the brain, it produces microscopic holes that makes the brain spongy. Patients start losing brain function one after another over the course of months. There is no treatment and it is almost always fatal.