Prions

Last February, The Westland/Hallmark Meat Co. of Chino, Calif., recalled 143.4 million pounds of beef contaminated with meat from cattle that were susceptible to mad cow disease as well as E. coli and salmonella bacteria.
The meat went to about 37 million pounds went to government nutrition programs, including schools, since October 2006.
The chance of consumers being exposed to mad cow disease is “negligible,” the U.S. Department of Agriculture said. Nearly all the meat has been consumed or is being withheld from distribution. Still it warrants concern. The incidence of prion diseases such as mad cow disease is on the rise.

A prion, short for proteinaceous infectious particle, is an infectious agent which hypothetically is composed only of protein. Prions cause a number of diseases including bovine spongiform encephalopathy (BSE aka “mad cow disease”) in a variety of mammals, including cattle and humans. All known prion diseases affect the structure of neural tissue, including the brain, and all prion diseases are currently untreatable and fatal.

The Term “Prion” can refer to both the theoretical unit of infection or the specific protein (e.g. PrP) that is thought to be the infectious agent, whether or not it is in an infective state.

Protein is fascinating biologically. All animals and insects must have protein to survive. Whole protein does not exist in a natural state on Earth. So animals have to synthesize whole protein from it’s constituent parts: animo acids. Proteins are necessary because they can fold into a nearly infinite number and type of shapes. The shapes themselves dictate biologic function mechanically. These proteins form the building blocks of nerve tissue and muscle as well as DNA and RNA. Bacteria and viruses are basically highly complex aggregations of protein.

As an animal goes through it’s day, due to random chance, a few proteins per thousand will become “unfolded.” These are normally electrically “washed out” of the brain during sleep.

Prions are believed to infect and propagate by refolding abnormally into a protein structure which is able to convert normal molecules of the protein into the abnormally structured form. All known prions induce the formation of an amyloid fold, in which the protein polymerises into an aggregate consisting of tightly packed beta sheets. This altered structure is extremely stable and accumulates in infected tissue, causing cell death and tissue damage. This stability means that prions are resistant to denaturation by chemical and physical agents, making disposal and containment of these particles difficult.

Proteins showing prion behaviour are also found in some fungi. This has been very important in helping to understand mammalian prions. However, fungal prions do not appear to cause disease in their hosts and may even confer an evolutionary advantage through a form of protein-based inheritance.

Human Prion Diseases
• Creutzfeldt-Jakob Disease (CJD)
• Variant Creutzfeldt-Jakob Disease (vCJD)
• Gerstmann-Straussler-Scheinker Syndrome
• Fatal Familial Insomnia
• Kuru

Prion diseases or transmissible spongiform encephalopathies (TSEs) are a family of rare progressive neurodegenerative disorders that affect both humans and animals. They are distinguished by long incubation periods, characteristic spongiform changes associated with neuronal loss, and a failure to induce inflammatory response. As you can see from the slide below, it turns a cows brain into swiss cheese, almost literally.