They can be transmitted From person to person: Iatrogenically, via organ and tissue transplants, use of contaminated neurosurgical instruments, or, rarely, blood transfusion (as in vCJD); or via cannibalism (as in kuru) From animal to person: Via ingestion of contaminated beef (as in vCJD) Prion diseases are not known to be contagious through casual person-to-person contact.