Difference between Viroids and Prions

What are Viroids?

Viroids are plant pathogens, which are much simpler than viruses. Structurally, these plant pathogens are smaller in size, comprising single-stranded, circular RNA molecules having 250-370 nucleotides. Viroids cannot replicate on their own, as their RNA does not encode to any gene products.

These pathogens cause several infectious diseases in both plants and animals. In plants, viroid infections result in severe mechanical damage to plants.

Some diseases that are caused by the infection of viroids in plants are chrysanthemum stun, citrus exocortis, cucumber pale fruit, etc.

In humans, Hepatitis D is the only infectious disease caused by the viroid and it is mainly transmitted from one person to another via blood or serum.

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What are Prions?

Prions are infectious agents, which are responsible for several neurodegenerative diseases in mammals. These infectious agents are primarily composed of sialoglycoprotein – a combination of sialic acid and glycoprotein and usually lack nucleic acid.

In 1982, Stanley Prusiner, an American neurobiologist proposed that the prions are an infectious protein. Based on his discoveries, he also proposed that they were responsible for the cause of scrapie. Scrapie is a type of neurological disease, affecting the nervous systems of animals, especially sheep and goats. Later, he coined the term prion for proteinaceous infectious.

In both humans and animals, these infectious agents cause a variety of neurodegenerative diseases and are mainly caused due to the abnormal folding of the proteins in the brain.

In humans, Down’s syndrome, Fatal familial insomnia, Alzheimer’s disease are a few examples of diseases caused by prions.

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Let’s learn the differences between viroids and prions.

Viroids and Prions- Comparisons

Viroids are infectious RNA molecules. Prions are infectious protein particles.
Viroids are smaller than viruses. Prions are smaller than the viroids.
Composed of
Viroids are composed of single strands of RNA. Prions are composed of only protein molecules.
Viroids are more complex. Prions are less complex.
Nucleic Acid
Present Absent
Protein Components
Absent Present
Viroids infect only plants. Prions mainly cause neuro-degenerative diseases.
Type of Diseases
Citrus exocytic
Tomato apical stunt
Potato spindle tuber
Grapevine yellow speckle
Chrysanthemum stunt disease
Mad cow diseases in cattle
Scrapie in sheep and goats
Creutzfeldt-Jakob disease in humans
Gerstmann-Straussler- syndrome in humans
Treatment / Cure
Traditional antiviroid methods have been employed for treating the infections caused by these viroids. Currently, there is no treatment or cure for neurodegenerative diseases, because prions are extremely difficult to destroy as they are resistant to chemicals, heat, radiation and even standard sterilisation procedures.


Also Refer: Difference Between Virus And Bacteria

This article concludes the introduction to viroids and prions and their differences.

Stay tuned to BYJU’S Biology to learn more in detail about the different types of microbes, pathogens and the list of infectious diseases, along with their causes, symptoms, and their treatments.

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