Creutzfeldt jakob disease? where's the virus from? where does it hide?

Not a virus: Cjd is not a virus (i.e., no dna or rna). It is called a prion and is thought to be from misfolding of naturally occurring prion protein. We think most prion disease occurs spontaneously although we don't know why. Some is genetic, and rarely it is transmitted from affected people who donate organs or from animals, e.g., mad cow disease. Unknown if environmental sources commonly affect humans.