Imagine your brain literally turning to sponge. That鈥檚 just what happens in a family of diseases known as the 鈥渟pongiform encephalopathies鈥� which leave the brain riddled with holes. In humans, spongiform encephalopathies include Creutzfeldt-Jakob Disease (CJD), Kuru, Fatal Familial Insomnia (FFI) and Gerstmann-Straussler-Scheinker Syndrome (GSSS).
These relatively rare diseases didn鈥檛 get much publicity until 鈥渕ad cow disease鈥� entered our vocabulary. This novel variant of CJD was linked to eating meat from cows that had been given feed supplements made from the remains of sheep that suffered from a disease known as scrapie. But nobody could figure out how the disease was transmitted since no unusual viruses, bacteria or fungi were to be found. Then came a startling theory. The infection was transmitted by proteins! This came as a surprise to the scientific community because all other infectious agents that had previously been encountered contained genetic information in the form of DNA. The discovery of these proteins, termed 鈥減rions鈥�, 鈥� as a new biological principle of infection 鈥撯�� earned Dr. Stanley Prusiner the Nobel Prize for Physiology or Medicine in 1997.
Prions, like all proteins, are composed of long chains of amino acids linked together. They exist in two forms. The first, PrPc, is found in abundance in nerve cells. Its exact function is unknown but it is thought to be innocuous. The second form, PrPsc, is the one that is commonly referred to as 鈥減rion鈥� and is the one that causes the problems. It can lead to death because the body does not recognize it as foreign and does not mount any immune response against it.
The normal PrPc protein and the mutated PrPsc protein both have the same amino acid sequence, but they fold differently. PrPc is coiled in tight alpha-helices, much like a spring, whereas PrPsc is folded like a rope into one dimensional layers known as beta sheets. When these two proteins come into contact, the PrPsc induces the normal PrPc to convert into the dangerous form. PrPsc cannot be digested by the cell, clogs up the cellular machinery and destroys the cell. It then leaks out of the dead cells ready to infect others, propagating a chain reaction.
Prions can infect people in three different ways. The first mode of transmission is 鈥渋nfectious鈥�, through the ingestion of prion-containing foods. This has been particularly worrisome, since prions are very resistant to disinfectants, high temperatures and UV- irradiations. Prions may also be 鈥渋nherited,鈥� because a certain version of the PrPc gene, the gene that gives the cell instructions for making the PrPc protein, can mutate into the PrPsc form. Unfortunately, prions can also appear 鈥渟poradically鈥� for no apparent reason. Spongiform encephalopathy is a terrifying concept but luckily it is rare. You are far more likely to be struck by lightning than by prions.
More information may be found on the Nobel Prize site:
However, many in the scientific community believe that the marketing of antibacterial products is simply preying on people鈥檚 fear of infection and contamination. Antibacterial products represent up to one-billion-dollars in revenue out of the 2.2 billion dollars that the hand wash market generates.
