Prions are infectious proteins that cause various fatal diseases in animals and humans, primarily affecting the brain. Prion diseases are usually transmitted through the ingestion of contaminated meat, especially the brain, of the same species. The most famous prion disease is mad cow disease, which can apparently jump species to infect humans. There are four primary prion diseases in humans, including Creutzfield-Jakob disease, Gerstmann-Straussler-Scheinker syndrome, fatal familial insomnia, and kuru.
Prions are infectious proteins, responsible for a variety of diseases in different animals, including humans. The word prion is a portmanteau of “proteinaceous” and “infectious.” They were first theorized in the 1960s and their existence and nature confirmed in the early 1980s.
There are many different types of disease caused by prions. All prion diseases affect the recipient’s brain and none are treatable, resulting in death. Recent developments could eventually lead to a vaccine in the future.
In animals, prions usually attack one or two closely related species. The disease known as scrapie is a prion disease that attacks sheep and goats. Prions are responsible for mink encephalopathy in minks. Chronic wasting disease affects some species of deer and moose, and feline encephalopathy and feline spongiform encephalopathy attack cats.
Perhaps the most famous disease caused by prions is the so-called bovine spongiform encephalopathy, more commonly called mad cow disease. Mad cow disease was unknown until the late 20th century and its discovery came as a shock to most people. While it’s not as serious in cattle as other livestock diseases — especially foot and mouth disease — it received a huge amount of attention when it was discovered that it could apparently jump species to infect humans.
Most of these diseases caused by prions have as their transmission vector the ingestion of contaminated meat, especially the brain, of the same species. Because modern practices often use ground bones and waste meat as a protein supplement for livestock, many cattle ingested other cattle, including brain tissue. It appears that lowering some temperature guidelines for sterilization in the UK allowed prions to move freely and a small-scale epidemic soon ensued.
In humans, there are four primary diseases caused by prions. The first, Creutzfield-Jakob disease, has a variant, known as vCJD, which appears to be transmitted by ingestion of contaminated beef. vCJD is the most common of the prion diseases in humans, but it is still relatively rare, infecting only one in every million people. Like all prion diseases, vCJD attacks the brain. Symptoms include dementia, which progresses very rapidly, followed by hallucinations, severe memory loss, seizures, loss of motor function, and finally death. The time from onset to final death from vCJD is quite short, rarely more than a few months, sometimes less than a few weeks.
Gerstmann-Straussler-Scheinker syndrome (GSS) is another disease in humans caused by prions, although much less common than vCJD. GSS is thought to affect only one in a hundred million people, making it incredibly rare. The cause of GSS is thought to be a genetic change and the exact vector is unknown. GSS victims experience dementia and loss of coordination, resulting in death. Life expectancy for victims of GSS is better than those with vCJD, but it rarely exceeds a few years.
Fatal familial insomnia is another disease in humans that has recently been discovered to be caused by prions. The disease has been known and documented since the late 1970s, but it was not until the 1990s that the prion responsible was discovered. FFI is usually initially characterized by chronic insomnia, which in turn leads to many psychological dysfunctions. Later, delusions and hallucinations occur, after which the ability to sleep disappears altogether. Finally, after about a year from the onset, the patient dies.
Kuru is the latest and first discovery of the common human diseases known to be caused by prions. Kuru is also known as the laughing sickness, due to the delirious laughter that often accompanies it. It was first discovered in parts of New Guinea in the early 20th century, particularly in the South Fore region. This region had a high prevalence of ritual cannibalism and it is now known that it was the consumption of human brain tissue responsible for disease transmission.
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