Proteinaceous infectious particles or Prions as they are commonly known are infectious agents which are entirely made up of protein material. They are misfolded proteins, and although, they do not multiply, they affect the brain structure and cause normally folded protein to convert to an abnormal prion form.
These infectious disease causing pathogens are a form of a protein called Cellular Prion Protein (PrPc). Mostly detected on the cell surface of the central nervous system, PrPc is also found in other bodily tissues. Prions are known to cause transmissible spongiform encephalopathies (TSEs). TSEs are neurodegenerative conditions that can infect both human beings and certain species of animals. The two most notable conditions are Creutzfeldt-Jakob disease (CJD) in humans and Bovine Spongiform Encephalopathy (BSE) or the mad cow disease in cattle and livestock.
Discovery of Prions
Biophysicist John Stanley Griffith and Radiation Biologist Tikvah Alper, conducted research during the 1960s and developed a hypothesis that an infectious agent consisting only of proteins is responsible for the cause of some TSEs. They noted that the agent responsible for causing the CJD disease and scrapie resisted ionizing radiation which is otherwise capable of destroying an entire infectious particle.
American Neurologist and Biochemist, Stanley B. Prusiner of University of California, San Francisco, worked with his team and purified the hypothetical infectious prion in 1982. They identified that the infectious agent consisted mainly of a specific protein. However, they managed to isolate and identify the infectious protein as Prion only two years later in 1984. The specific protein that Prion was made up of is known as Prion Protein (PrP). This research won Prusiner a Nobel Prize in 1997.
Categorization & Transmission of Prion Diseases
Prion diseases are subdivided into three categories, depending on how the disease was contracted –
sporadic, familial and acquired. The cause of a sporadic prion disease is unknown. People get infected by this disease with unknown risk factors or gene mutations.
The typical symptoms of sporadic prion disease are memory loss, impaired thinking, anxiety or depression, and imbalance and incoordination. Once these symptoms present themselves, the disease progresses rapidly and is usually fatal within a few months.
The familial or inherited prion disease is caused due to a faulty gene that has possibly been passed on from a previous generation. The symptoms are similar to that of the sporadic disease and account for 15% of prion diseases.
Acquired prion diseases are very rare and account for less than 1% of known cases.
This type of infection is due to exposure to abnormal prion protein. It is mostly contracted on consumption of
BSE infected food. In rare cases, the infection is a result of blood transfusion contaminated by the disease or surgical instruments.
In animals, the primary cause of contracting the infection is through ingestion. Prions linger in the environment through saliva, urine and other body fluids, and remains of dead animals. They may be deposited in the soil and contaminate minerals.
Research on Potential Treatments
It is discovered that lichens reduce the spread of prions to other proteins in the body. Astemizole, a histamine, is known to have anti-prion activity. Scientists are able to identify compounds using advanced computer modelling that can treat diseases caused by prions, stabilize conformation and reduce the amount of harmful PrPs. While the progression of the disease can be slowed down, more research needs to be done as there is yet no known cure for Prion disease.