Cyclovirus

Cyclovirus is a genus of small, circular, single-stranded DNA viruses in the family Circoviridae. Members have compact genomes typically about 1.7 to 2.0 kilobases in length and encode two major open reading frames: replication-associated protein (Rep) and the capsid protein (Cap) in opposite orientations. The genomes contain a conserved nonanucleotide motif at the origin of replication within a stem-loop structure, a hallmark of circoviruses. Replication is thought to proceed by rolling-circle replication, aided by the Rep protein’s initiator motifs and helicase activity; Cap forms the virion shell.

Cycloviruses have been detected in a wide range of hosts and environments. Sequences have been recovered from various animals, including mammals and birds, and from environmental samples such as wastewater. Detection methods include targeted PCR and metagenomic sequencing, which have revealed substantial genetic diversity and numerous distinct cyclovirus lineages. The full host range and biology of many cycloviruses remain poorly understood.

In humans, cyclovirus DNA or sequences have occasionally been found in clinical samples, including cerebrospinal fluid or brain tissue, but a causal link to disease has not been established. Overall, cycloviruses are considered to be genetically diverse and widespread in nature, with ongoing research aimed at clarifying their host range, replication biology, and potential associations with disease. Taxonomically, they are recognized as a genus within the family Circoviridae by ICTV, separate from other circoviruses and including multiple provisional species described from sequence data.