Difference between Virus and Viroid

Virus is an obligate intracellular parasite which can reproduce only by invading and taking over other cells as they lack the cellular machinery for self reproduction.

Viroids are subviral, smallest known agents of infectious disease. The term viroid was coined by T.O. Diener (1971) to describe the causal agent of the potato spindle tuber disease (PSTV). There are some 25 viroids which vary in nucleotide sequence.

Viroids are spread by plant propagation (cuttings and tubers) through seeds and by manual mishandling with contaminated implements

Both Virus and viroids  are strict intracellular, sub cellular infectious agents, always requires a living host for replication

Virus vs Viroid

Virus

1. It is a nucleoprotein particle 

2. Nucleic acid can be DNA or RNA  

3. A protein covering or coat called capsid is present around the genetic material

         4.  Genetic material replication and protein synthesis using machinery                 of the host

              Replication mode: lytic and lysogenic cycle

5. Virus has a larger size. 

6. Virus infects all types of organisms

Animal viruses, plant virus, Mycovirus, Bacteriophage

Viroid

1. It is an infectious RNA particle 

2. Viroid is formed of only of single stranded RNA 

3. A protein coat is absent

          4. Viroid replication proceeds through an RNA-based rolling-circle mechanism using RNA pol II                of host

5. Viroid has a smaller size

6. Viroid infects only plants; Potato spindle tuber viroids (PSTV) 1st viroid discovered

Tomato plant macho viroid (TPMVd), Avocado sunblotch viroid (ASBVd), Peach latent mosaic viroid (PLMVd) 

 

*Virusoids are viroids located inside protein coat of true virus. RNA is linear or circular and non infections                                                                                                Updated October 2020