Circovirus
Baltimore Classification
Higher order taxa
Viruses; ssDNA viruses; Circoviridae; Circovirus
Species
Beak and feather disease virus, Canary circovirus, Goose circovirus
Description and Significance
Circoviruses are very small non-enveloped icosahedral viruses with a single stranded circular DNA genome. They have been described in pigs (porcine circovirus, PCV), chickens (chicken anemia virua, ChAV), psittacines (psittacine beak and feather disease virus, PBFD) and pigeons. The virus targets the lymphoid tissue and causes immunosuppression in the host.
Circoviruses are the smallest pathogenic DNA viruses that have been identified and characterized in animals.
Genome Structure
The genome of the circovirus is monomeric. It is unsegmented and contains a single molecule of circular, ambisense, sinle-stranded DNA that forms a covalently closed circle. The complete genome is 1800-2000 nucleotides long and the genome has a guanine+cytosine content of 48.4-53.1 %. (source: ICTV dB Descriptions)
Virion Structure of a Circovirus
The virions of a circovirus consist of a capsid that is enveloped. Virions have an extracellular phase during their life cycle. The virions are not tailed. The capsid is round and exhibits icosahedral symmetry (T=13). It is isometric and has a diameter of 17-22 nm, although the size of particle diameter varies with the type of stain used. The capsids appear round and the capsid surface structure reveals a regular pattern with distinctive features. The capsid consists of 32 capsomers. The capsomers are hollow morphological subunits. (source: ICTV dB Descriptions)
Reproduction Cycle of a Circovirus in a Host Cell
Viral Ecology & Pathology
References
Leslie W. Woods, DVM, PhD, Dipl ACVP, and Kenneth S. Latimer, DVM, PhD, Dipl ACVP; "Circovirus Infection of Nonpsittacine Birds"; Journal of Avian Medicine and Surgery 14(3):154–163, 2000
