Why prions are contagious? I want a professional answer.

The essence of prions is protein. This virus is different from other viruses because it has no nucleic acid.

Protein has different structures, and prions are just different structures of normal protein. For example, a normal person is standing, and a person who can't stand straight at ordinary times is a patient, which shows that the surface structure is different. Protein with abnormal prion structure has a function, which can affect similar protein with normal structure and make them as abnormal as it, so more and more normal protein has become protein with abnormal structure.

The technical term is

There are two conformations of prion protein: normal type (PrPc) and pathogenic type (PrPsc). They are isomers, encoded by the same chromosome gene PRNP, and their amino acid sequences are exactly the same. Their molecular weights are all between 33 and 35 KD, and the fundamental difference lies in their conformational differences.

Replication mechanism: The pathogenic (PrPsc) protein can be used as a "seed" to induce the transformation of the normal (PrPc) protein to the pathogenic type.

See: aho.com/links/xdxmsy/2006-1/2006-11-6.htm for details.