Definition and Discovery of Prions Prions are characterized by folded protein molecules that do not contain any genetic information. “Prions are composed of amino acids, which are the essential building blocks of proteins”. The word prion, which is also called proteinaceous infectious particles, often refers to the abnormally folded proteins which can change other proteins from their normal state to an abnormal one (Prion Fact Sheet). Unlike other infectious agents like viruses, bacteria, fungi, and parasites, prions do not have a genome. Prions are simple proteins that do not contain any genetic material. Though prions also cause diseases, the lack of genetic material distinguishes them from the other infectious agents. Prion proteins have two forms: the normal and undamaging protein or the PrPc and the harmful and disease-causing protein or the PrPSc (Prusiner). “A chain reaction is formed when a conversion from PrPc to PrPSc occurs”. Long slender strands aggregates are formed when an ample amount of PrPSc protein is made. Prions convert the normal proteins, which are similarly composed of amino acids, into prions like themselves by entering the cells. Prions cause diseases that are neurodegenerative by extracellularly accumulating within the central nervous system and forming plaques known as amyloids which messes up the normal tissue structure by creating holes in the tissue (Prion disease). Prions were discovered by Stanley B. Prusiner, an American neurologist from the University of California. He was awarded the 1997 Nobel Prize in Medicine or Physiology for discovering a new genre of disease-causing agents which do not have any genes or genetic material (Weiss). The Nobel Prize came after two decades of trying to prove that strange infectious proteins could cause diseases in the brain like the mad cow disease which affects both animals and people, while he was ignored and even ridiculed by his peers. His peers assumed that the diseases were caused by undiscovered and slow-growing viruses and not infectious proteins. The first recorded disease caused by a prion, but which was not recognized then as being a prison-related infection, was Kuru. The disease Kuru was found in the isolated New Guinea Fore tribe. The disease spread or was transmitted because of the tribe’s religious practice of eating the brain tissue of their dead relatives, which they do by grinding the brain into a pale grey soup and then heating it (Prion Diseases). It was speculated that the brain tissue that was ingested by some members of the tribe was infected. When the practice of ingesting brain tissue was stopped, the occurrence of the disease declined, and eventually, the disease never arose within the tribe again. Another significant event relating to prion infection was the 1986 Mad Cow epidemic in England This, however, still did not drive scientists to suspect harmful proteins as the cause of infection, instead they suspected a possibility that slow viruses may be the cause as these viruses spend decades inflicting harm and disorder in their hosts and are hard to isolate (Guyer). Effects of Prions on Animals and Humans Prions infect both animals and humans. They cause fatal diseases. There