http://www-micro.msb.le.ac.uk/3035/prions.html
Prions do not have a nucleic acid genome. It seems that a protein alone is the infectious agent. The infectious agent has been called a prion. A prion has been defined as "small proteinaceous infectious particles which resist inactivation by procedures that modify nucleic acids". The discovery that proteins alone can transmit an infectious disease has come as a considerable surprise to the scientific community.
Prion diseases are often called spongiform encephalopathies because of the post mortem appearance of the brain with large vacuoles in the cortex and cerebellum. Probably most mammalian species develop these diseases. Specific examples include:
* Scrapie: sheep
* TME (transmissible mink encephalopathy): mink
* CWD (chronic wasting disease): muledeer, elk
* BSE (bovine spongiform encephalopathy): cows
Humans are also susceptible to several prion diseases:
* CJD: Creutzfeld-Jacob Disease
* GSS: Gerstmann-Straussler-Scheinker syndrome
* FFI: Fatal familial Insomnia
* Kuru
* Alpers Syndrome
Humans might be infected by prions in 2 ways:
1. Acquired infection (diet and following medical procedures such as surgery, growth hormone injections, corneal transplants) i.e. infectious agent implicated.
2. Apparent hereditary mendelian transmission where it is an autosomal and dominant trait. This is not prima facie consistent with an infectious agent.
Empasis:
>>>Kuru is the condition which first brought prion diseases to prominence in the 1950s. Found in geographically isolated tribes in the Fore highlands of New Guinea. Established that ingesting brain tissue of dead relatives for religious reasons was likely to be the route of transmission. They ground up the brain into a pale grey soup, heated it and ate it. Clinically, the disease resembles CJD. Other tribes in the vicinity with same religious habit did not develop the disease. It is speculated that at some point in the past a tribe member developed CJD, and as brain tissue is highly infectious this allowed the disease to spread. Afflicted tribes were encouraged not to ingest brain tissue and the incidence of disease rapidly declined and is now almost unknown.<<<