Caliciviridae

The Caliciviridae family are a family of viruses, members of Class IV of the Baltimore scheme. They are positive-sense, single stranded RNA which is non-segmented. The caliciviruses have been found in a number of organisms such as humans, cattle, pigs, cats, chickens, reptiles, dolphins and amphibians. The caliciviruses have a simple construction and are not enveloped. The capsid appears hexagonal/spherical and has icosahedral symmetry with a diameter of 35â€"39 nm.

Caliciviruses are not very well studied because until recently they could not be grown in culture, and there is no suitable animal model. However, the recent application of modern genomic technologies has led to an increased understanding of the virus family. A recent isolate from rhesus monkeysâ€"Tulane virusâ€"can be grown in culture and this system promises to increase our understanding of these viruses.

The name calicivirus is derived from the Greek word calyx meaning cup or goblet. This name is appropriate as many strains have visible cup-shaped depressions.

Taxonomy

The Caliciviridae family include the following genera:

• Genus Lagovirus; type species: Rabbit hemorrhagic disease virus
• Genus Nebovirus;
• Genus Norovirus; type species: Norwalk virus
• Genus Sapovirus; type species: Sapporo virus
• Genus Vesivirus; type species: Vesicular exanthema of swine virus

Two additional genera have been proposed: Recovirus for a novel calicivirus detected in stool specimens from rhesus monkeys and Valovirusâ€"for a novel group of swine caliciviruses known as the St-Valérien-like viruses. These genera have yet to be officially approved. There are a number of other unclassified caliciviruses including the chicken calicivirus.

Virology

All viruses in this family possess a non segmented, polyadenylated, positive sense single stand RNA genome of ~7.5â€"8.5 kilobases in length, enclosed in an icosahedral capsid of 27â€"40 nanometers in diameter.

Transmission

Transmission of caliciviruses is generally by the fecal-oral route but can also be transmitted via the respiratory route.

Human disease

Calicivirus infections commonly cause acute gastroenteritis, which is the inflammation of the stomach and intestines (e.g. the Norwalk Virus). Symptoms can include vomiting and diarrhea. These symptoms emerge after an incubation time of 2 days and the symptoms only generally last for 3 days. Most calicivirus infections do not call for medical attention, but those who are immunocompromised may need to be hospitalized for rehydration therapy.

Animal viruses

Feline calicivirus (FCV)â€"a member of the Vesivirusâ€"represents an important pathogen of cats.

Sapovirus, Norovirus and Vesivirus have been detected in pigs, making this animal species of particular interest in the study of calicivirus pathogenesis and host range.

The first mouse norovirus, murine norovirus 1 (MNV-1), was discovered in 2003. Since then, numerous murine norovirus strains have been identified and they were assigned a new genogroup in the genus Norovirus.

Rabbit hemorrhagic disease virus (RHDV) is a pathogen of rabbits that causes major problems throughout the world where rabbits are reared for food and clothing, make a significant contribution to ecosystem ecology, and where they support valued wildlife as a food source.

Note

Australia and New Zealand, in an effort to control their rabbit populations, have intentionally spread calicivirus.