Sorry about your friend First; I am not an expert on human prion disease and second I apologize for being off topic. A prion is just an abnormal misshapen protein. Viruses that cause them to occur in humans do exist. The particular CWD and MCD conditions are not viral but I'm guessing your friend had some sort of prion involvement in his brain. Many people with ALZ and other CNS conditions have prions in their brain and for those of you invested in AVXL; they've spoken about protein misfolding in ALZ for years. Stupid for me to interpret what the doctor meant but I'm guessing he meant the damage to the brain was similar to mad cow but the cause was not. Probably mentioned viral as the cause but probably knew prions are not viruses.