I. Introduction
Viruses belonging to the Caliciviridae family possess a single-stranded, linear, positive-sense RNA genome. The human pathogens within this family are of the Norovirus and Sapovirus genera and are known to cause acute gastroenteritis.
II. Epidemiology/ Geographic distribution
Caliciviruses have a worldwide distribution and noroviruses are a major cause of epidemic non-bacterial gastroenteritis.
III. Genome Structure
The Caliciviridae viruses are characterized as having small, positive-sense, single-stranded RNA genomes. The complete genome is approximately 7400-8300 nucleotides in length.
IV. Physical properties of virion
Virions consist of a non-enveloped capsid that is spherical or hexagonal in appearance and exhibits icosahedral symmetry. The capsid has a diameter of approximately 35-39 nm.
V. Replication
The replication process is not completely understood. It is proposed that this process begins with the attachment of viral proteins to host receptors resulting in entry of the virus into the cell by endocytosis. Acidification of endocytic vesicles induces fusion and uncoating of the virion resulting in the release of the RNA genome into the cytoplasm. Translation is followed by RNA replication. Virus particles are assembled via intracellular budding and then released.
VI. Disease
Calicivirus infections (Norovirus and Sapovirus) cause gastroenteritis. Common signs/ symptoms are nausea, vomiting and diarrhea lasting for only a few days.
VII. Transmission
The common mode of transmission is fecal-oral route (ingestion of contaminated food or water), but direct person-to person transmission is also possible through the inhalation of aerosol droplets.
VIII. Treatment
Normally infections do not require medical attention. Severe illness is rare but may occur in immunocompromised individuals. Rehydration therapy may be used in these instances.
IX. Prevention
Handwashing is an effective preventative measure. Sanitizing surfaces is also recommended in preventing the spread of infection.