The prions are proteinaceous infectious particles, formed only by a modified form of a normal protein from the cell membrane of the neuron. The prions multiply transforming normal proteins into infectious proteins. Both types of proteins are composed of the same amino acid sequence, but differ in three-dimensional structure.
Diseases caused by prions are often fatal and are called transmissible spongiform subacute encephalopathies (TSEs), due to the characteristic spongy appearance of the brain of affected individuals. The best known are lumbar pruritus ("scrapie") or sheep scrapie and bovine spongiform encephalopathy or "mad cow disease", and in humans Creutzfeldt-Jacob disease.
The disease BSE or bovine spongiform encephalopathy, is a disease caused by prions, and that can be transmitted to humans through the consumption of parts of infected animals, especially nerve tissues.
The spongiform encephalopathy bovine or "disease mad cow disease" is a disease whose first cases of sick animals declared in the United Kingdom in 1986. In 1996 was detected in humans a new disease, variant Creutzfeldt-Jakob disease, which was linked to the “mad cow disease” epidemic.
It is a degenerative disease of the central nervous system of bovines, characterized by the appearance of nervous symptoms in adult animals that progressively ends with the death of the animal.
The appearance of these diseases was related to feeding the cows with feed supplements containing the remains of sheep that suffered from scrapie.