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Virus classification Edit this classification
(unranked): Virus
Realm: Monodnaviria
Kingdom: Shotokuvirae
Phylum: Cressdnaviricota
Class: Arfiviricetes
Order: Cirlivirales
Family: Circoviridae

Circoviridae is a family of DNA viruses.[1][2] Birds and mammals serve as natural hosts. There are 101 species in this family, assigned to 2 genera. Diseases associated with this family include: PCV-2: postweaning multisystemic wasting syndrome; CAV: chicken infectious anemia.[3][4]


Viruses in the family Circoviridae are non-enveloped, with icosahedral and round geometries, and T=1 symmetry.[2] The diameter is around 20 nm. Genomes are circular and non-segmented, around 3.8kb in length. The capsid consists of 12 pentagonal trumpet-shaped pentamers.[3] There are two main open reading frames arranged in opposite directions that encode the replication and capsid proteins. Alternative start codons are common in the avian species.[citation needed]

Genus Structure Symmetry Capsid Genomic arrangement Genomic segmentation
Cyclovirus Icosahedral T=1 Non-enveloped Circular Monopartite
Circovirus Icosahedral T=1 Non-enveloped Circular Monopartite

Life cycle[edit]

Viral replication is nuclear. Entry into the host cell is achieved by penetration into the host cell. Replication follows the ssDNA rolling circle model. DNA templated transcription, with some alternative splicing mechanism is the method of transcription. The virus exits the host cell by nuclear egress, and nuclear pore export.[2][3] A stem loop structure with a conserved nonanucleotide motif is located at the 5' intergenic region of circovirus genomes and is thought to initiate rolling-cycle replication. Birds and mammals serve as the natural host. Transmission routes are fecal-oral.[2][3]

Genus Host Tissue tropism Entry Release Replication site Assembly site Transmission
Cyclovirus Birds Chicken: Thymocytes, erythrobalstoid cells; Egg: embryonal tissues and eggshell membrane Cell receptor endocytosis Budding Nucleus Nucleus Horizontal: oral-fecal; vertical: bird to egg
Circovirus Birds; pigs None Cell receptor endocytosis Budding Nucleus Nucleus Horizontal; oral-fecal


The family Circoviridae contains two genera—Circovirus and Cyclovirus.


A cyclovirus—cyclovirus-Vietnam—has been isolated from the cerebrospinal fluid of 25 Vietnamese patients with CNS infections of unknown aetiology.[6] The same virus has been isolated from the faeces of healthy children and also from pigs and chickens. This suggests an orofaecal route of transmission with a possible animal reservoir.[6]

See also[edit]


  1. ^ Breitbart, Mya; Delwart, Eric; Rosario, Karyna; Segalés, Joaquim; Varsani, Arvind (2017). "ICTV Virus Taxonomy Profile: Circoviridae". Journal of General Virology. 98 (8): 1997–1998. doi:10.1099/jgv.0.000871. PMC 5656780. PMID 28786778.
  2. ^ a b c d e f "ICTV Report Circoviridae".
  3. ^ a b c d "Viral Zone". ExPASy. Retrieved 15 June 2015.
  4. ^ "Virus Taxonomy: 2020 Release". International Committee on Taxonomy of Viruses (ICTV). March 2021. Retrieved 11 May 2021.
  5. ^ Dayaram, A; Potter, K. A; Moline, A. B; Rosenstein, D. D; Marinov, M; Thomas, J. E; Breitbart, M; Rosario, K; Arguello-Astorga, G. R; Varsani, A (2013). "High global diversity of cycloviruses amongst dragonflies". Journal of General Virology. 94 (Pt 8): 1827–40. doi:10.1099/vir.0.052654-0. PMID 23596268.
  6. ^ a b Tan, L. V; Van Doorn, H. R; Nghia, H. D. T; Chau, T. T. H; Tu, L. T. P; De Vries, M; Canuti, M; Deijs, M; Jebbink, M. F; Baker, S; Bryant, J. E; Tham, N. T; Bkrong, N. T. T. C; Boni, M. F; Loi, T. Q; Phuong, L. T; Verhoeven, J. T. P; Crusat, M; Jeeninga, R. E; Schultsz, C; Chau, N. V. V; Hien, T. T; Van Der Hoek, L; Farrar, J; De Jong, M. D (2013). "Identification of a New Cyclovirus in Cerebrospinal Fluid of Patients with Acute Central Nervous System Infections". mBio. 4 (3): e00231–13. doi:10.1128/mBio.00231-13. PMC 3684831. PMID 23781068.

External links[edit]