40 - Viroids, prions

Question 1

Viroids

Answer 1

• Contain only nucleic acid (ø proteins)
• Found in plants
  
  • But recently also in hepatitis D
• Made of circular RNA
• Morphology:
  
  • ​Circular
  • +ssRNA
  • Superhelical
  • No structural proteins
• Resistance: extremely strong
  
  • 100 °C, 30 min, UV and gamma radiation, disinfectants – no effect
• Biological properties:
  
  • ​Plant pathogens – only in cultivated plants
  • Infection via gardening tools, injuries
  • Mechanical transmission
  • Host spectrum: varies, no orphan viroid
• Antigenic properties: not antigenic

Question 2

Viriods

List some viriods

Answer 2

• Potato spindle tuber viroid
• Hop stunt viroid
• Coconut cadang-cadang viroid

Question 3

Prions

Answer 3

• Agensts of spongiform encephalotpathies
• Proteins of infectious nature
• Proteinaceous infectous particles
• Morphology:
  
  • ​Pure (ø nucleic acid)
    
    • Only made of proteins
• Resistance: extremely high
  
  • 136-138 °C, 20 min
• Biological properties:
  
  • ​Cellular prion protein (PrP^c)
    
    • Normal component of the neurons (cytoskeleton, messenger)
  • Infectious prion proteins (PrP^sc)
    
    • _​_PrP^c and PrP^sc differ in three amino acids in humans
    • Isoform: α-helix → β-shee
      
      • This creates protein deposits. When these protein deposits are cleaned up from the brain, huge holes are found in the brain → disease
    • Develops protease resistance and accumulate in neuron
• Host spectrum:
  
  • ​Uncertain
  • Can be isolated in vitro (ø in vivo)
• Pathogenesis:
  
  • Intestine → spleen, lymph nodes (6 months) → nerves
  • Reach the CNS – modulator proteins: induce neurons to produce PrP^sc
  • → intracellular accumulation, aggregation, polymerization
    
    • Amyloid plaques (3-4 years) – neuron degeneration
    • → spongiform encephalopathy
• Antigenic properties:
  
  • ​Not antigenic, recognized as own (therefore no antibodies)
• Diagnosis:
  
  • ​Clinical signs
  • Histopathology: vacuolization of neurons, amyloid plaques
  • Proteinas K digestion + IF, Western blot, ELISA

Question 4

Prions

Transmissible spongiform encephalopathies

Answer 4

• Scrapie
  
  • ​Incoordination, swaying, itching
• Bovine spongiform ecephalopathy (BSE)
  
  • ​Scrapie modification
  • Behavior changes - “mad cow syndrome”
• Feline spongiform ecephalopathy
  
  • ​BSE modification
• Transmissible mink encephalopathy
• Human: progressive dementia
  
  • Kuru
    
    • ​Caused by cannibalism
    • Similar to scrapie
  • Gatal familial insomnia
    
    • ​Trouble sleeping
    • Caused by mutation of the PrP^c protein

Question 5

In which group can virods and prions be categorized into?

Answer 5

Subvral antigens​

They are macromolecules which either contain nucleic acid or protein