The Caliciviridae are a family of "small round structured" viruses, members of Class IV of the Baltimore scheme. Caliciviridae bear resemblance to enlarged picornavirus and was formerly a separate genus within the picornaviridae.[1] They are positive-sense, single-stranded RNA which is not segmented.[2] Thirteen species are placed in this family, divided among eleven genera.[3] Diseases associated with this family include feline calicivirus (respiratory disease), rabbit hemorrhagic disease virus (often fatal hepatitis), and Norwalk group of viruses (gastroenteritis).[3][4] Caliciviruses naturally infect vertebrates, and 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 (T=1[5] or T=3[6][4]) with a diameter of 35–39 nm.[7]
Caliciviruses are not very well studied because until recently, they could not be grown in culture, and they have a very narrow host range and no suitable animal model. However, the recent application of modern genomic technologies has led to an increased understanding of the virus family.[7] A recent isolate from rhesus monkeys—Tulane virus—can be grown in culture, and this system promises to increase understanding of these viruses.[8]
Calici- comes from the Latin word Calyx and the Greek word kalyx. The words mean a cup or chalice, a Calix. This comes from the strains having visible cup-shaped depressions.
All viruses in this family possess a nonsegmented, polyadenylated, positive-sense, single-strand RNA genome around 7.5–8.5 kilobases in length, enclosed in an icosahedral capsid of 27–40 nanometers in diameter.[citation needed]
Viral replication is cytoplasmic. Entry into the host cell is achieved by attachment to host receptors, which mediate endocytosis. Replication follows the positive-stranded RNA virus replication model. Positive-stranded RNA virus transcription is the method of transcription. Translation takes place by leaky scanning, and RNA termination-reinitiation. Vertebrates serve as the natural host. Transmission routes are fecal-oral.[4]
Calicivirus infections commonly cause moderate to severe 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 require medical intervention, but those who are immunocompromised may need to be hospitalized due to serious fluid loss.[citation needed]