ICTV Virus Taxonomy Profile: Circoviridae

Abstract

The family Circoviridae comprises viruses with small, circular, single-stranded DNA (ssDNA) genomes, including the smallest known animal viruses. Members of this family are classified into two genera, Circovirus and Cyclovirus, which are distinguished by the position of the origin of replication relative to the coding regions and the length of the intergenic regions. Within each genus, the species demarcation threshold is 80 % genome-wide nucleotide sequence identity. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the taxonomy of the Circoviridae, which is available at www.ictv.global/report/circoviridae.

Fig. 1.

(a) 3D reconstruction of porcine circovirus 2 using cryo-electron microscopy. A structural model comprising 60 subunits (T=1) arranged in 12 pentameric morphological units has been proposed [1]. (b) Negative-stained transmission electron micrograph of porcine circovirus 2 (provided by Carolina Rodríguez-Cariño and Joaquim Segalés, CReSA, Spain). Scale bar=20 nm.

Fig. 2.

Genome schematics illustrating the major open reading frames (ORFs) characteristic of members of the family Circoviridae. Members of the family have two major ORFs encoding replication-associated (Rep) and capsid (Cp) proteins, as well as a conserved nonanucleotide motif marking the origin of replication. The nonanucleotide motif sequence is depicted through sequence probability logos generated in Weblogo 3. The rep gene of human-associated cyclovirus 8, a representative of the Cyclovirus type species, is interrupted by an intron.