CJD ( Creutzfeld Jacob Disease) is a degenerative neurological disorder in which the brain becomes porous and spongy in appearance. Caused by misshapen prions in the human brain. Prions are a vital neurological protein and although they cannot replicate themselves directly, when a disease causing prion is introduced to a healthy brain, it forces the normal prions into it’s misshapen structure. Thus causing a chain reaction in which more and more misshapen proteins are formed until eventual death.
The only way to get CJD is to either have one of your prions spontaneously mutate (very rare) or through ingestion of contaminated foods or direct contact with blood. Among the Fore Tribe in Papua New Guinea there have been outbreaks caused by the presence of CJD in a member of their deceased, who was then ingested as part of their cannibalistic funeral ceremony, leading to a small epidemic within the tribe whereby more and more members were being infected, dying and then going on to infect others.