Proteinaceous Infectious Particles
Uploaded by Xerxes on Sep 21, 2005
Over the years there have been many documented cases of diseases for which there appeared to be no cause. Only within the late 20th century has the reason for these illnesses been brought into the spotlight. The symptoms of these illnesses are usually the loss of coordination followed by dementia, but in some cases an inability to sleep develops into dementia. These symptoms are caused by damaged regions of the brain. This damage occurs in the form of normal tissue changing to a sponge-like consistency. This is caused by cells clumping together and dying, leaving holes in the brain. These diseases fall into the category of spongiform encephalopathies (Collinge, 1995). This type of disease can occur in all mammals and is named after the mammal in which it is found. For example, in cows it is called bovine spongiform encephalopathy, or more commonly known as “mad cow disease”. Spongiform encephalopathies may also occur in humans in the form of Creutzfeldt-Jakob disease or Kuru, the latter of which was only found in the Fore tribe of Papua, New Guinea, members of which ate the brains of the dead as a sign of respect. Cannibalism was ended in 1958 due to health concerns. After the deaths of the 2600 afflicted persons, not a single case of Kuru has been recorded.
The cause of spongiform encephalopathy is a small protein called a prion, or “proteinaceous infectious particle”. The protein was discovered and named in 1982 by Dr. Stanley B. Prusiner of the Department of Neurology at the University of California School of Medicine. At first, the discovery endured a great deal of skepticism due to the long accepted theory that only microbes can cause disease, which was proposed by Louis Pasteur. The prion protein (PrP for short) was first imagined when the agent that causes scrapie (the type of spongiform encephalopathy which occurs in sheep) was thought to lack nucleic acid (Alper, 1972). This was determined by subjecting infected tissue to ultraviolet or ionizing radiation, both of which are known to degrade nucleic acid. Afterwards, the tissue was injected into the brain tissue of a healthy subject. The infectivity of the tissue remained the same. This proved that there was no nucleic acid present in the infective agent, due to the fact that if it had been a viral or bacterial infection, the nucleic acid within the virus or bacteria would have been destroyed...