Carlavirus

Carlavirus, formerly known as the "Carnation latent virus group", is a genus of viruses in the order "Tymovirales", in the family "Betaflexiviridae". Plants serve as natural hosts. There are 53 species in this genus. Diseases associated with this genus include: mosaic and ringspot symptoms.
Description.
"Carlavirus" is described in the 9th report of the ICTV (2009). The genus is characterised by having six ORFs (Open Reading Frames) including a TGB (Triple Gene Block). The viruses are transmitted by insects.
Taxonomy.
The genus was first proposed in the first report of the ICTV in 1971, as the 'Carnation latent virus group' but was renamed in 1975 as the 'Carlavirus group', and as the genus "Carlavirus" in 1995 (6th report). In 2005 (8th report) it was placed in the "Flexiviridae" family, having previously been unassigned. The current position in the 9th report (2009) as a genus of the family "Betaflexiviridae" derives from the subsequent subdivision of "Flexiviridae".
The following species are assigned to the genus:
Virology.
The virions are non enveloped, filamentous, 610–700 nanometers (nm) and 12–15 nm in diameter.
The linear 5.8–9 kilobase genome is positive sense, single-stranded RNA. The 3’ terminus is polyadenylated. In some species the 5’ end is capped. The genome encodes 3 to 6 proteins including a coat protein located at the 3' end and an RNA-dependent RNA polymerase located at the 5' end of the genome.
Life cycle.
Viral replication is cytoplasmic, and is lysogenic. Entry into the host cell is achieved by penetration into the host cell. Replication follows the positive stranded RNA virus replication model. Positive stranded RNA virus transcription is the method of transcription. The virus exits the host cell by tripartite non-tubule guided viral movement. Plants serve as the natural host.
Transmission.
Infection is at times spread by aphids in a semi-persistent mode, that is, the vector is infective for a number of hours.(Pimentel) Some species are transmitted by "Bemisia tabaci" in a semi-persistent mode or through the seed. Most species infect only a few hosts and cause infections with few or no symptoms, for example, American hop latent virus and lily symptomless virus. Some, such as blueberry scorch virus and poplar mosaic virus, cause serious illnesses. (Foster)