Viroids: infectious nucleic acids, are pathogens that contained nucleotide bases without a protein coat (subviral particles)

• Smaller than viruses
• Contain no nucleic acids
• Only contains PrP (protein)
• No capsid/protein coat
• Misfolded protein in brain cells

Viroids

• Small, single-stranded
• Circular RNA particles
• Much simpler than a virus
• Infectious proteins

• Neural tissues in animals and humans
  

Viroids

• Almost all plant tissues
  
• Human liver tissue

• Humans
• Animals (with hooves)

• Cattle (Bovine Spongiform Encephalopathy)
• Sheep (Scrapie)

Viroids

• Plants

• Potatoes, cucumbers, tomatoes, chrysanthemums, avocados, and coconut palms
• Humans (recent discovery)

• Person/Animal-Person/Animal
  
• Ingestion
  
• Infections
  
• Mutations in gene, encoding the protein
  

Viroids

• Contamination by seeds, planting (human hands/tools), insects
  

• Humans
• Kuru-spread from human to human from cannibalism leads to loss of motor control and unusual behaviors, such as uncontrolled bursts of laughter, followed by death
• Creutzfeldt-Jakob disease (CJD)- acquired from eating beef from animals with BSE, still exists in various areas, disease spreads from human to human by blood
• Animals
• MAD COW DISEASE (BSE)-spread by the consumption of meat, nervous tissue, or internal organs between members of the same species and lead to developed lesions or “holes” in the brain, causing the brain tissue to resemble a sponge
• Scrapie- animal scrapes off its wool or hair because it has a neurological irritation

• Humans
• Hepatitis D- occurs when simultaneous infection of a cell with both the hepatitis B virus and the hepatitis D viroid, extensive sequence between the hepatitis D viroid RNA and human liver cell 7S RNA, a small cytoplasmic RNA that is a component of the signal recognition particle, the structure involved in the translocation of secretory and membrane particles, causes liver cell death by sequestering and/or cleaving this 7S RNA
• Plants
• Potato Sprindle Tuber (PSTVd)- located in potatoes and tomatoes and causes them to become misshaped and deformed caused by environmental conditions

• Memory loss
  
• Insomnia
  
• Communication problems
  
• Unsteadiness
  
• Hallucinations
  
• Seizures
  

• Prion bind to single molecule of the normal PrP protein, prion then catalyzed the normal PrP protein into a prion. It occurs by the normal PrP protein folding until its shape is close to a prion.

• Diseases caused by prions are not curable and are indestructible, but their growth can be slowed by medication
  

http://www.atsu.edu/faculty/chamberlain/Website/Lects/Prions.htm

http://www.ehow.com/info_8283747_viroids-prions.html

http://www.prion.ucl.ac.uk/clinic-services/information/signs-and-symptoms/