Prions in the Body and Creutzfeldt-Jakob Disease (CJD)

Updated on September 6, 2017
AliciaC profile image

Linda Crampton is a writer and teacher with a first class honors degree in biology. She often writes about the scientific basis of disease.

BSE, a prion disease, affects many different breeds of cattle. It can also trigger disease in humans.
BSE, a prion disease, affects many different breeds of cattle. It can also trigger disease in humans. | Source

What Are Prions?

Prions are misfolded proteins that can cause some very serious diseases. Unfortunately, their formation and behaviour isn't completely understood. Researchers are trying to unlock the mysteries of these small but potentially deadly particles.

The normal proteins in our body are essential molecules with complex, folded shapes. The shape of a protein enables it to do its job. If a protein is folded incorrectly or becomes unfolded it can no longer function. A prion (pronounced "preeon") is a misfolded protein with a special ability. It can change other protein molecules into prions. These can then alter the shape of even more proteins in a chain reaction.

Prions are the causal agents of some horrible illnesses known as prion diseases. These often progress rapidly once symptoms appear and (at the moment) are always fatal. The most common prion disease is Creutzfeldt-Jakob disease, or CJD. A variant of this disease has appeared in people who have eaten contaminated meat from a cow suffering from bovine spongiform encephalopathy, or BSE. BSE is a prion disease in cattle. It's also known as Mad Cow disease.

An illustration showing myoglobin (a muscle protein) and the complex, folded structure of a functional protein; the folds are held in place by chemical bonds
An illustration showing myoglobin (a muscle protein) and the complex, folded structure of a functional protein; the folds are held in place by chemical bonds | Source

Pathogens: Infectious Agents That Cause Disease

Most infections are caused by viruses, bacteria, and fungi, including yeasts. Infectious agents that cause disease are known as pathogens. Like human cells, pathogens contain DNA (or, in the case of some viruses, a similar chemical called RNA). DNA and RNA belong to the nucleic acid family. Nucleic acids contain genes. The genes contain a code that controls a pathogen's structure and behaviour and enables it to cause an infection.

A prion consists of protein and has no nucleic acid or genetic code. The discovery that prions could reproduce in our body and cause disease was at first very hard for scientists to accept. Although they now know that this happens, they still have many questions about how and why prions form and about how they function.

Scrapie in sheep was the first prion disease to be discovered.
Scrapie in sheep was the first prion disease to be discovered. | Source

Difference Between Normal Prion Proteins and Prions

Prion proteins are common in our body and occur in two varieties. One is a normal and necessary part of our cells while the other (the prion) is dangerous. Prions not only transform useful proteins into harmful ones but also form protein clumps.

Cellular or Normal Prion Proteins

A cellular prion protein (PrPc) is a normal constituent of cells and is folded correctly. Cellular or normal prion proteins are located throughout the body but are especially abundant in the brain. They seem to be very important in the life of cells, although their exact function isn't known. They may play a role in preventing cells from being damaged.

Abnormal Prion Proteins or Prions

An abnormal prion protein that is folded incorrectly and has the ability to cause other proteins to become misfolded is often known as simply a "prion". It's symbolized by PrPsc. The "sc" stands for scrapie, the first prion disease to be discovered. Scrapie damages the nervous system of sheep.

Prion Formation and Activity

How Are Prions Made?

Prions may appear in our body for several reasons.

  • They may enter the body from another organism.
  • They may be made in our bodies due to altered genes. Genes contain instructions for making proteins. Some inherited genes may contain a mutation (a change in a gene) that alters the structure of the gene and causes it to code for a misfolded prion protein, or prion.
  • Normal prion proteins may spontaneously change into prions.

Prion Formation

Transmissible Spongiform Encephalopathies

Prion diseases are quite rare in humans (as far as we know), but they are very unpleasant for the sufferers. They affect the brain more than any other body part and cause neurodegeneration.

Prion diseases are also known as Transmissible Spongiform Encephalopathies, or TSEs. They are known as spongiform diseases because they cause nerve tissue to break down and make the brain look as though it has spaces resembling the pores of a sponge.

The "holes" that are visible in the brain of a cow with BSE;  similar holes develop in a person with a TSE, or Transmissible Spongiform Encephalopathy
The "holes" that are visible in the brain of a cow with BSE; similar holes develop in a person with a TSE, or Transmissible Spongiform Encephalopathy | Source

Classic Creutzfeldt-Jakob Disease, or CJD

About 1 in a million people develop Creutzfeldt-Jakob Disease or CJD every year. In the United States, the incidence of CJD is about 200 to 300 cases per year.

Symptoms of CJD include a personality change, depression, vision problems, loss of muscle coordination, balance problems, jerky movements, slurred speech, memory loss, and impaired thinking and judgement. Eventually patients are unable to walk or feed themselves and lose awareness of their surroundings. Death is usually due to pneumonia, respiratory failure, or heart failure.

Since there is no cure for CJD, the goal of treatment is to relieve pain and make the patient feel as comfortable as possible. Research into finding an effective treatment or cure is continuing.

More Information About Creutzfeldt-Jakob Disease

Types of Creutzfeldt-Jakob Disease

There are three main types of classic Creutzfeldt-Jakob Disease.

  • Sporadic CJD is the most common type. It develops when normal prion proteins in the patient's body spontaneously change into abnormal ones. The cause of this change is unknown. The prions that are made can transform other normal prion proteins.
  • Sporadic CJD generally develops in people aged 45 or older. The disease usually lasts for six or seven months after the first symptom appearance, but some people have died after only a few weeks while others have lived for a year or more.
  • Familial CJD develops due to inherited genes. The genes produce abnormal prion proteins in people aged about 50 or older. This form of CJD is much rarer than the sporadic form.
  • A very rare disease called iatrogenic CJD is spread by a transplant of contaminated tissue from an infected person or by the use of contaminated surgical equipment.

Some people have become sick from vCJD after eating contaminated meat.
Some people have become sick from vCJD after eating contaminated meat. | Source

Variant Creutzfeldt-Jakob Disease or vCJD

Creutzfeldt-Jakob disease and variant Creutzfeldt-Jakob disease are both prion diseases. Although the diseases have similar names, there are major differences between them.

  • vCJD was discovered in the United Kingdom in 1996. It's a relatively new disease compared to CJD, which was discovered in 1920.
  • All people who have developed variant Creutzfeldt-Jakob disease have lived in a country inhabited by cows with BSE. CJD hasn't been linked to BSE.
  • Researchers believe that with the exception of three people, everyone to date who has become ill with vCJD became infected by eating contaminated beef. The three exceptions are thought to have become infected by receiving contaminated blood during a transfusion.
  • Cow meat is the muscle of a cow. It can become contaminated with BSE prions when material from the brain or nervous system enters the meat. This could happen when processing equipment cuts through the spinal cord and then touches the meat, for example.
  • Median age of death from CJD in the United States is 68 while median age of death from vCJD in the United Kingdom is 28.
  • Each disease causes specific differences in the appearance of brain tissue.
  • The first symptoms of vCJD are generally psychiatric or sensory problems. The patient develops the dementia that is typical of CJD later.
  • People with variant Creutzfeldt-Jakob disease tend to live for longer after diagnosis than patients with classic Creutzfeldt-Jakob disease (about ten to fourteen months for people diagnosed with vCJD and around six months for people with classic CJD).

Stained clumps of prions in tonsil tissue from a vCJD patient
Stained clumps of prions in tonsil tissue from a vCJD patient | Source

Incubation Period for vCJD

In 2013, an interesting report was published in the British Medical Journal. The researchers collected data which suggests that 1 in 2000 people in the UK could have the vCJD prions in their body, even though they aren't sick. The data was obtained by examining appendixes removed from people around the country.

The number of vCJD cases in the UK peaked in 2000 and has fallen since then. Prion diseases seem to have an incubation period, which sometimes lasts for many years. During the incubation period no symptoms are present. Once the symptoms appear, the disease progresses rapidly. Some researchers suggest that vCJD might have an incubation period of about ten years, given that UK cases peaked about ten years after a recent BSE outbreak. Others suggest that the incubation period may be much longer.

The data described in the British Medical Journal is interesting, but scientists are cautious about their interpretation of the data. They say that infected people could remain asymptomatic for the rest of their lives. On the other hand, the prions could be in their incubation period and the infected people could eventually develop a prion disease. Not enough is known about prion biology to predict the outcome of the infection.

Harmful prions seem to affect the brain most strongly.
Harmful prions seem to affect the brain most strongly. | Source

Prion Biology

Prion biology is fascinating and important. Even though the diseases caused by prions are quite rare, they are devastating for patients and their families. In addition, some other serious human disorders involve misfolded and misbehaving proteins and seem to operate in a similar way to prion diseases. These disorders include Alzheimer's disease and Parkinson's disease. Understanding prion diseases could help us to understand these health problems and even to treat them more effectively.

It may be that the effects of prions in our bodies are more widespread and common than we realize. We certainly don't understand the biology of the particles very well yet. For example, a few experimental drugs have been created that slow prion replication in the lab. A 2013 report described the apparent development of drug resistance in prions. Drug resistance normally develops in cells with nucleic acid, such as bacterial cells. The puzzle of how it could develop in protein molecules is one of the many aspects of prions that needs to be explained. There is still a great deal to learn about these mysterious particles and their role in health and disease.

References

  • "Prion Diseases." Centers for Disease Control and Prevention. https://www.cdc.gov/prions/index.html (accessed September 6, 2017).
  • "Creutzfeldt-Jakob Disease Fact Sheet." National Institutes if Health. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Creutzfeldt-Jakob-Disease-Fact-Sheet (accessed September 6, 2017).
  • "Variant Creutzfeldt-Jakob Disease Information." World Health Information. http://www.who.int/mediacentre/factsheets/fs180/en/ (accessed September 6, 2017).
  • Callaway, Ewen. "One in 2,000 UK people might carry vCJD proteins." Nature. http://www.nature.com/news/one-in-2-000-uk-people-might-carry-vcjd-proteins-1.13962#/ (accessed September 6, 2017).
  • Walker, Lary C. "Prions May Devslop Drug Resistance: The Implications for Mad Cow, Alzheimer's and Parkinson's." Scientific American. https://blogs.scientificamerican.com/mind-guest-blog/prions-may-develop-drug-resistance-the-implications-for-mad-cow-alzheimere28099s-and-parkinsone28099s/ (accessed September 6, 2017).

Questions & Answers

    © 2013 Linda Crampton

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      • AliciaC profile image
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        Linda Crampton 3 years ago from British Columbia, Canada

        Thank you very much, Arachnea. I appreciate your visit. The existence of prions certainly is scary. I hope scientists learn more about them soon.

      • Arachnea profile image

        Tanya Jones 3 years ago from Texas USA

        I recall this topic from my Biology class. I swore off fast food for a very long time as a result. This is a very informative hub. Great job.

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thanks for the kind comment and for sharing the interesting information, Jamie. It can't be easy or pleasant to work with tissue that may be infected with prions!

      • jhamann profile image

        Jamie Lee Hamann 4 years ago from Reno NV

        Well researched and well written hub. I work in Pathology and I remember back about ten years ago if we got suspected brain tissue we would spend half the day decontaminating. Jamie

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you very much for the visit and the comment, Audrey. The existence of prions is certainly worrying. Hopefully researchers will soon discover better ways of dealing with the problem.

      • AudreyHowitt profile image

        Audrey Howitt 4 years ago from California

        This is such an informative hub on the subject--I have been a vegetarian for many years, and so do not worry so much about this disease--but I worry for others

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Bill, that is so sad. I am very sorry that you lost your friend, and I'm sorry for his or her family, too. I hope that an effective treatment or cure for prion diseases is discovered very soon.

      • bdegiulio profile image

        Bill De Giulio 4 years ago from Massachusetts

        Hi Linda, Sadly we know all too well about prion disease and CJD. A very good friend of ours died from this a few years ago. To say that this is scary is an understatement. What happened to our friend in just 3 to 4 months was so sad and heart-wrenching, and as you know, there is nothing that can be done. Great job explaining this.

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you very much for the comment, Minnetonka Twin. I'm sorry for the woman in the video, too. It must be frightening for her to know that she could get such a horrible disease.

      • Minnetonka Twin profile image

        Linda Rogers 4 years ago from Minnesota

        Wow Alicia~This is a very scary disease and I had never heard the term 'prions.' I have heard of mad cow disease and how dangerous it is to humans. I sure hope they learn more about this disease. I feel so sad for the woman in the video, not knowing if and when she will get the disease. At least she has the right attitude about how to live her life. Great article!

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thanks for the visit and the comment, Deb. It's sad that mad cow disease still occurs, both for the cows and for us.

      • aviannovice profile image

        Deb Hirt 4 years ago from Stillwater, OK

        Now I finally know what happens regarding meat ingestion of animals afflicted with mad cow disease. Thanks for bringing this up.

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thanks for the comment, Cynthia. I hope that a cure will be found for prion diseases soon, too. They are horrible disorders.

      • CMHypno profile image

        CMHypno 4 years ago from Other Side of the Sun

        Informative hub as always Alicia. There is still so much more to learn about the human body and what causes disease. Hopefully research will continue and some kind of treatment/cure will be found for sufferers.

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you very much, Nell. I appreciate your comment as well as the vote and the share!

      • Nell Rose profile image

        Nell Rose 4 years ago from England

        Hi Alicia, that was really interesting, I never knew what a prion was, but of course had heard of 'mad cow disease' which is the illness with the cows, great information, voted up and shared! nell

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you very much for the votes and the pin, FlourishAnyway. I appreciate your visit and comment!

      • FlourishAnyway profile image

        FlourishAnyway 4 years ago from USA

        What a fascinating but also scary hub. With all of this Mad Cow Disease I am so glad I don't eat red meat any longer. Voted up and more, plus pinned.

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you very much, drbj. Prions are scary to think about, especially since they can be so dangerous. It would be so good if we knew how to prevent their formation or how to stop them from becoming active!

      • drbj profile image

        drbj and sherry 4 years ago from south Florida

        Absolutely, positively fascinating discourse about prions, Alicia. Thank you for your research and expertise. Though I think I felt better when I was less prion-educated!

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you for the visit and the comment, DDE.

      • DDE profile image

        Devika Primić 4 years ago from Dubrovnik, Croatia

        Prions in the Body and Human Disease very important information, a useful and well researched hub.

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you very much, Crafty! I think we may be hearing a lot more about prions in the future. They are fascinating - but very worrying - particles. I hope researchers learn how to treat prion diseases and other protein folding disorders very soon.

      • CraftytotheCore profile image

        CraftytotheCore 4 years ago

        What an amazing article! You obviously spent a lot of time and effort in to this and I find it so educational. I've heard of this but never read so much about it before.

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you very much for the visit and the lovely comment, Bill!

      • billybuc profile image

        Bill Holland 4 years ago from Olympia, WA

        You do know your stuff, Alicia! If I had been taught this in high school I would have zoned out halfway through the lecture. This was interesting enough to keep me going all the way. Well done!

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you so much for the kind comment and the support, Faith. I always appreciate your visits and blessings!

      • Faith Reaper profile image

        Faith Reaper 4 years ago from southern USA

        Alicia, you always come up with fascinating topics for hubs indeed! As Sue stated above, you have written it so that all are able to understand the information. We do not eat much red meat at all any longer, and may not at all after reading all of this information! Pretty scary stuff to say the least.

        Thank you for always writing such excellent hubs! Up and more and sharing

        Blessings, Faith Reaper

      • AliciaC profile image
        Author

        Linda Crampton 4 years ago from British Columbia, Canada

        Thank you very much for the comment, Sue. I appreciate your vote and shares as well!

      • Sue Bailey profile image

        Susan Bailey 4 years ago from South Yorkshire, UK

        Thanks Alicia that was so interesting and although a complicated subject, the way you presented the information was easy to understand. Voted up, pinned and shared.

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