<unk>  is a type of transmissible spongiform encephalopathy (TSE), which are caused by prions. Prions are misfolded proteins that occur in the neurons of the central nervous system (CNS). They are thought to affect signaling processes, damaging neurons and resulting in degeneration that causes the spongiform appearance in the affected brain. The<unk>  prion is dangerous because it promotes refolding of native prion protein into the diseased state. The number of misfolded protein molecules will increase exponentially and the process leads to a large quantity of insoluble protein in affected cells. This mass of misfolded proteins disrupts neuronal cell function and causes cell death. Mutations in the gene for the prion protein can cause a misfolding of the dominantly alpha helical regions into beta pleated sheets. This change in conformation disables the ability of the protein to undergo digestion. Once the prion is transmitted, the defective proteins invade the brain and induce other prion protein molecules to misfold in a self-sustaining feedback loop. These neurodegenerative diseases are commonly called prion diseases. People can also develop<unk>  because they carry a mutation of the gene that codes for the prion protein (PRNP). This occurs in only 5–10% of all<unk>  cases. In sporadic cases, the misfolding of the prion protein is a process that is hypothesized to occur as a result of the effects of aging on cellular machinery, explaining why the disease often appears later in life. An EU study determined that "87% of cases were sporadic, 8% genetic, 5% iatrogenic and less than 1% variant." Transmission MRI of iCJD because of growth hormone The defective protein can be transmitted by contaminated harvested human brain products, corneal grafts, dural grafts, or electrode implants and human growth hormone. It can be familial (fCJD); or it may appear without clear risk factors (sporadic form: sCJD). In the familial form, a mutation has occurred in the gene for PrP, PRNP, in that family. All types of<unk>  are transmissible irrespective of how they occur in the person. It is thought that humans can contract the variant form of the disease by eating food from animals infected with bovine spongiform encephalopathy (BSE), the bovine form of TSE also known as mad cow disease. However, it can also cause sCJD in some cases. Cannibalism has also been implicated as a transmission mechanism for abnormal prions, causing the disease known as kuru, once found primarily among women and children of the Fore people in Papua New Guinea. While the men of the tribe ate the muscle tissue of the deceased, women and children consumed other parts, such as the brain, and were more likely than men to contract kuru from infected tissue. Prions, the infectious agent of<unk> , may not be inactivated by means of routine surgical instrument sterilization procedures. The World Health Organization and the US Centers for Disease Control and Prevention recommend that instrumentation used in such cases be immediately destroyed after use; short of destruction, it is recommended that heat and chemical decontamination be used in combination to process instruments that come in contact with high-infectivity tissues. Thermal depolymerization also destroys prions in infected organic and inorganic matter, since the process chemically attacks protein at the molecular level, although more effective and practical methods involve destruction by combinations of detergents and enzymes similar to biological washing powders.
Creutzfeldt–Jakob disease
Anti-Hu associated encephalitis
Powassan encephalitis
Kuru (disease)  Kuru  1
Saint Louis encephalitis
Variant Creutzfeldt–Jakob disease  Variant Creutzfeldt–Jakob disease  1
Autoimmune encephalitis
Viliuisk encephalomyelitis