PRIONS: ON THE TRAIL OF KILLER PROTEINS
Earliest written record of Scrapie in English sheep; already prevalent in central Europe.
In the 1950s, a district medical officer working in the highlands of New Guinea observed a fatal disease among the people of the Fore (FOR-ay) tribe. The Fore people called this sickness kuru, which means "trembling in fear." After intially becoming unable to walk, victims of kuru lost the ability to swallow or chew. Drastic weight loss would inevitably lead to death. Today we know that kuru is one of several diseases in humans and animals caused by prion (PREE-on) proteins.
High levels of kuru appear among the Fore people of New Guinea.
Scientists experimentally transmit Kuru and CJD to chimpanzees, demonstrating the transmissible nature of these diseases.
60 people die from CJD after being infected by contaminated surgical instruments. 85 people die after receiving prion-infected growth hormone injections.
Diseases caused by prions are known as spongiform diseases, because the brain tissue in infected individuals is filled with holes, giving it a sponge-like appearance. Although prions are found throughout the brain, the symptoms of spongiform diseases vary according to the regions they are most concentrated in. There are currently no effective treatments for spongiform diseases and all are fatal.
Classic CJD or Creutzfeldt-Jakob disease (human)
. The most prevalent of the spongiform diseases
. Occurs spontaneously in 1 out of a million people
. 10% of cases are inherited mutations in the PRPN gene
. Usually strikes people age 50 to 75
. Symptoms: dementia, muscle twitching, vision problems
Dr. Stanley Prusiner coins the term "prion" (PROteinaceous INfectious particle). Highly purified PrP-res is shown to be infectious. He goes on to win the Nobel Prize in Medicine in 1997.
Fatal Familial Insomnia (human)
. All cases are inherited mutations in the PrP gene
. Usually strikes people age 36 to 61
. Disruption of sleep/wake cycle leads to coma, then death
Scrapie (goats, sheep)
. Occurs as infection in genetically susceptible sheep
. There is no evidence of spread to humans
BSE or Bovine Spongiform Encephalopathy (cattle)
. Also known as "Mad Cow Disease" because infected animals act strangely and can be aggressive
. Spread rapidly through Britain by rendering infected animals into cattle feed
Chronic Wasting Disease (deer, elk)
. Infectious disease in wild deer and elk primarily in the western United States
. Drooling, difficulty swallowing, weight loss
Scientists identify the PrP gene and discover that uninfected people produce a normal form of the PrP protein.
. Struck members of the Fore tribe in the 1950s and 1960s
. Muscle weakness, loss of coordination, tremors, inappropriate episodes of laughter or crying
. Transmitted by ritual cannibalism as part of funeral ceremonies
The idea that a protein alone could transmit disease has been around since the 1960s. New evidence has been stacking up to support this idea ever since. So why are some scientists still not convinced that prions transmit spongiform disease? Why are they still talking about the "protein only hypothesis?"
By the year 2000, nearly 180,000 cattle will become infected. To stop the spread, thousands of cattle are killed.
A new variant of CJD is linked to exposure to BSE from British beef. By April 2005, 155 U.K. residents are dead. Because of the long incubation period, cases of CJD due to this incident will likely surface well into the future. The mad cow story isn't over yet.
Prions cannot be destroyed by boiling, alcohol, acid, standard autoclaving methods, or radiation. In fact, infected brains that have been sitting in formaldehyde for decades can still transmit spongiform disease. Cooking your burger 'til it's well done won't destroy the prions!