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Allied Health Microbiology: 5.3 Prions

Allied Health Microbiology
5.3 Prions
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table of contents
  1. Cover
  2. Title Page
  3. Copyright
  4. Table Of Contents
  5. Preface
  6. Forward
  7. Chapter 1: An Invisible World
    1. 1.1 What Our Ancestors Knew
    2. 1.2 A Systematic Approach
    3. 1.3 Types of Microorganisms
    4. Summary
  8. Chapter 2: The Cell
    1. 2.1 Spontaneous Generation
    2. 2.2 Foundations of Modern Cell Theory
    3. 2.3 Unique Characteristics of Prokaryotic Cells
    4. Summary
  9. Chapter 3: Prokaryotic Diversity
    1. 3.1 Prokaryote Habitats, Relationships, and Microbiomes
    2. Summary
  10. Chapter 4: The Eukaryotes of Microbiology
    1. 4.1 Unicellular Eukaryotic Parasites
    2. 4.2 Parasitic Helminths
    3. 4.3 Fungi
    4. Summary
  11. Chapter 5: Acellular Pathogens
    1. 5.1 Viruses
    2. 5.2 The Viral Life Cycle
    3. 5.3 Prions
    4. Summary
  12. Chapter 6: Microbial Biochemistry
    1. 6.1 Microbial Biochemistry
    2. Summary
  13. Chapter 7: Microbial Growth
    1. 7.1 How Microbes Grow
    2. 7.2 Oxygen Requirements for Microbial Growth
    3. 7.3 The Effects of pH on Microbial Growth
    4. 7.4 Temperature and Microbial Growth
    5. Summary
  14. Chapter 8: Modern Applications of Microbial Genetics
    1. 8.1 Whole Genome Methods and Pharmaceutical Applications of Genetic Engineering
    2. 8.2 Gene Therapy
    3. Summary
  15. Chapter 9: Control of Microbial Growth
    1. 9.1 Controlling Microbial Growth
    2. 9.2 Testing the Effectiveness of Antiseptics and Disinfectants
    3. Summary
  16. Chapter 10: Antimicrobial Drugs
    1. 10.1 Fundamentals of Antimicrobial Chemotherapy
    2. 10.2 Mechanisms of Antibacterial Drugs
    3. 10.3 Mechanisms of Other Antimicrobial Drugs
    4. 10.4 Drug Resistance
    5. 10.5 Testing the Effectiveness of Antimicrobials
    6. 10.6 Current Strategies for Antimicrobial Discovery
    7. Summary
  17. Chapter 11: Microbial Mechanisms of Pathogenicity
    1. 11.1 Characteristics of Infectious Disease
    2. 11.2 How Pathogens Cause Disease
    3. 11.3 Virulence Factors of Bacterial and Viral Pathogens
    4. Summary
  18. Chapter 12: Disease and Epidemiology
    1. 12.1 The Language of Epidemiologists
    2. 12.2 Tracking Infectious Diseases
    3. 12.3 Modes of Disease Transmission
    4. 12.4 Global Public Health
    5. Summary
  19. Chapter 13: Innate Nonspecific Host Defenses
    1. 13.1 Physical Defenses
    2. 13.2 Chemical Defenses
    3. 13.3 Cellular Defenses
    4. 13.4 Pathogen Recognition and Phagocytosis
    5. 13.5 Inflammation and Fever
    6. Summary
  20. Chapter 14: Adaptive Specific Host Defenses
    1. 14.1 Overview of Specific Adaptive Immunity
    2. 14.2 Major Histocompatibility Complexes and Antigen-Presenting Cells
    3. 14.3 T Lymphocytes and Cellular Immunity
    4. 14.4 B Lymphocytes and Humoral Immunity
    5. 14.5 Vaccines
    6. Summary
  21. Chapter 15: Diseases of the Immune System
    1. 15.1 Hypersensitivities
    2. 15.2 Autoimmune Disorders
    3. 15.3 Organ Transplantation and Rejection
    4. Summary
  22. Chapter 16: Skin and Eye Infections
    1. 16.1 Anatomy and Normal Microbiota of the Skin and Eyes
    2. 16.2 Bacterial Infections of the Skin and Eyes
    3. 16.3 Viral Infections of the Skin and Eyes
    4. 16.4 Mycoses of the Skin
    5. 16.5 Helminthic Infections of the Skin and Eyes
    6. Summary
  23. Chapter 17: Respiratory System Infections
    1. 17.1 Anatomy and Normal Microbiota of the Respiratory Tract
    2. 17.2 Bacterial Infections of the Respiratory Tract
    3. 17.3 Viral Infections of the Respiratory Tract
    4. Summary
  24. Chapter 18: Urogenital System Infections
    1. 18.1 Anatomy and Normal Microbiota of the Urogenital Tract
    2. 18.2 Bacterial Infections of the Urinary System
    3. 18.3 Bacterial Infections of the Reproductive System
    4. 18.4 Viral Infections of the Reproductive System
    5. 18.5 Fungal Infections of the Reproductive System
    6. 18.6 Protozoan Infections of the Urogenital System
    7. Summary
  25. Chapter 19: Digestive System Infections
    1. 19.1 Anatomy and Normal Microbiota of the Digestive System
    2. 19.2 Microbial Diseases of the Mouth and Oral Cavity
    3. 19.3 Bacterial Infections of the Gastrointestinal Tract
    4. 19.4 Viral Infections of the Gastrointestinal Tract
    5. 19.5 Protozoan Infections of the Gastrointestinal Tract
    6. 19.6 Helminthic Infections of the Gastrointestinal Tract
    7. Summary
  26. Chapter 20: Circulatory and Lymphatic System Infections
    1. 20.1 Anatomy of the Circulatory and Lymphatic Systems
    2. 20.2 Bacterial Infections of the Circulatory and Lymphatic Systems
    3. 20.3 Viral Infections of the Circulatory and Lymphatic Systems
    4. 20.4 Parasitic Infections of the Circulatory and Lymphatic Systems
    5. Summary
  27. Chapter 21: Nervous System Infections
    1. 21.1 Anatomy of the Nervous System
    2. 21.2 Bacterial Diseases of the Nervous System
    3. 21.3 Acellular Diseases of the Nervous System
    4. Summary
  28. Creative Commons License
  29. Recommended Citations
  30. Versioning

5.3 Prions

Learning Objectives

  • Describe prions and their unique characteristics

Research attempts to discover the causative agents of previously uninvestigated diseases have led to the discovery of nonliving disease agents quite different from viruses. These include particles consisting only of RNA or only of protein that, nonetheless, are able to self-propagate at the expense of a host—a key similarity to viruses that allows them to cause disease conditions. To date, these discoveries include viroids, virusoids, and the proteinaceous prions.

Prions

At one time, scientists believed that any infectious particle must contain DNA or RNA. Then, in 1982, Stanley Prusiner, a medical doctor studying scrapie (a fatal, degenerative disease in sheep) discovered that the disease was caused by proteinaceous infectious particles, or prions. Because proteins are acellular and do not contain DNA or RNA, Prusiner’s findings were originally met with resistance and skepticism; however, his research was eventually validated, and he received the Nobel Prize in Physiology or Medicine in 1997.

A prion is a misfolded rogue form of a normal protein (PrPc) found in the cell. This rogue prion protein (PrPsc), which may be caused by a genetic mutation or occur spontaneously, can be infectious, stimulating other endogenous normal proteins to become misfolded, forming plaques (see Figure 5.10). Today, prions are known to cause various forms of transmissible spongiform encephalopathy (TSE) in human and animals. TSE is a rare degenerative disorder that affects the brain and nervous system. The accumulation of rogue proteins causes the brain tissue to become sponge- like, killing brain cells and forming holes in the tissue, leading to brain damage, loss of motor coordination, and dementia. Infected individuals are mentally impaired and become unable to move or speak. There is no cure, and the disease progresses rapidly, eventually leading to death within a few months or years.

Endogenous normal prion protein (PrPc) is converted into the disease-causing form (PrPsc) when it encounters this variant form of the protein. PrPsc may arise spontaneously in brain tissue, especially if a mutant form of the protein is present, or it may originate from misfolded prions consumed in food that eventually find their way into brain tissue.
Figure 5.10 Endogenous normal prion protein (PrPc) is converted into the disease-causing form (PrPsc) when it encounters this variant form of the protein. PrPsc may arise spontaneously in brain tissue, especially if a mutant form of the protein is present, or it may originate from misfolded prions consumed in food that eventually find their way into brain tissue. (credit b: modification of work by USDA)
Creutzfeldt-Jakob disease (CJD) is a fatal disease that causes degeneration of neural tissue. (a) These brain scans compare a normal brain to one with CJD. (b) Compared to a normal brain, the brain tissue of a CJD patient is full of sponge-like lesions, which result from abnormal formations of prion protein.
Figure 5.11 Creutzfeldt-Jakob disease (CJD) is a fatal disease that causes degeneration of neural tissue. (a) These brain scans compare a normal brain to one with CJD. (b) Compared to a normal brain, the brain tissue of a CJD patient is full of sponge-like lesions, which result from abnormal formations of prion protein. (credit a (right): modification of work by Dr. Laughlin Dawes; credit b (top): modification of work by Suzanne Wakim; credit b (bottom): modification of work by Centers for Disease Control and Prevention)

TSEs in humans include kuru, fatal familial insomnia, and Creutzfeldt- Jakob disease (see Figure 5.11). TSEs in animals include mad cow disease, scrapie (in sheep and goats), and chronic wasting disease (in elk and deer). TSEs can be transmitted between animals and from animals to humans by eating contaminated meat or animal feed. Transmission between humans can occur through heredity (as is often the case with CJD) or by contact with contaminated tissue, as might occur during a blood transfusion or organ transplant. There is no evidence for transmission via casual contact with an infected person.

Prions are extremely difficult to destroy because they are resistant to heat, chemicals, and radiation. Even standard sterilization procedures do not ensure the destruction of these particles. Currently, there is no treatment or cure for TSE disease, and contaminated meats or infected animals must be handled according to federal guidelines to prevent transmission.

image

  • Does a prion have a genome?

Link to Learning

For more information on the handling of animals and prion-contaminated materials, visit the guidelines published on the CDC website (https://www.openstax.org/l/22cdccontaminat) (inactive link as of 05/20/2021) and the WHO website (https://www.openstax.org/l/22whocontaminat).

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Copyright © 2019 by Open Stax and Linda Bruslind Allied Health Microbiology by Open Stax and Linda Bruslind is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted.
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