Viroid

Viroid
Virus classification
Informal group:	Subviral agents
(unranked):	Viroid

Viroids are the smallest infectious pathogens known. They consist solely of short strands of circular, single-stranded RNA without protein coats. They are mostly plant pathogens (plant diseases), some of which can cause crop loss.^[1]

Viroid genomes are extremely small in size. They are about 80 times smaller than the smallest virus.^[2] The human pathogen (causes diseases in humans) hepatitis D virus is a defective RNA virus^[3] similar to viroids.^[4]

Viroids were the first "sub-viral pathogens" discovered and named by Theodor Otto Diener. He was a plant pathologist at the U.S Department of Agriculture's Research Center in Beltsville, Maryland, in 1971.^[5][6] The first viroid to be identified was the Potato spindle tuber viroid (PSTVd). About 33 species have been identified.

1. ↑ Hammond, Rosemarie W. ; Owens, Robert A. "Viroids: new and continuing risks for horticultural and agricultural crops". The American Phytopathological Society. Retrieved 7 August 2015.{{cite web}}: CS1 maint: multiple names: authors list (link)
2. ↑ Dasgupta M.K. Principles of Plant Pathology (New Delhi: Allied Publishers, 1988), p. 132
3. ↑ A defective virus cannot make copies of itself outside of a living host cell
4. ↑ Alves C, Branco C, Cunha C (2013). "Hepatitis delta virus: a peculiar virus". Adv Virol. 2013: 560105. doi:10.1155/2013/560105. PMC 3807834. PMID 24198831.
5. ↑ Diener TO (August 1971). "Potato spindle tuber "virus". IV. A replicating, low molecular weight RNA". Virology. 45 (2): 411–28. doi:10.1016/0042-6822(71)90342-4. PMID 5095900.
6. ↑ "ARS Research Timeline – Tracking the Elusive Viroid". 2006-03-02. Retrieved 2007-07-18.