Caliciviridae

The family Caliciviridae (caliciviruses) take their name from the 32 cup-shaped depressions (calix, Lat. = calyx) located on each of the icosahedral quintuple and triple axes. In negatively stained virus preparations, some cup-shaped depressions appear distinct and well defined, while in others these depressions are less pronounced.

The capsid itself consists of 90 dimers of a single viral structural protein, the major structural protein VP1, which in its dimerized form builds up into an icosahedron. Attached to the linear ss(+)RNA, only 1-2 copies are found of a second structural protein(VP2), whose function is poorly understood. Calicivirus virions are small (27 to 40 nm), icosahedral, and nonenveloped. In general, caliciviruses are stable in the environment. Many strains are resistant to inactivation by heat and certain chemicals such as ether, chloroform, and mild detergents(which allows them to survive in the acidic stomach environment and cause gastroenteritis).

The family Caliciviridae includes the human pathogenic genera:

• Norovirus with the species Norwalkvirus (trigger of gastroenteritis) and
• Sapovirus with the species Sapporovirus (causative agent of gastroenteritis).
• Furthermore, the family Caliciviridae includes the non-human pathogenic genera:
• Lagovirus
• Vesivirus and
• Nebovirus

The viruses are excreted in large quantities via stool and vomit, accordingly, transmission occurs via direct contact (oral ingestion of virus-containing droplets - aerosols produced during gushing vomiting) or indirect contact (fecal-oral, e.g. via hand contact with contaminated surfaces). Although viral shedding is possible in the presymptomatic phase, the massive release of infectious viruses begins with the onset of clinical symptoms. This explains the rapid spread of infection, for example in inpatient facilities. Transmission of noroviruses can also occur through contaminated food or drinking water. Although infections can occur all year round, an accumulation is observed in the winter months ("winter vomiting disease").

Children (approx. 30% of cases) and adults (approx. 50% of cases) are affected. Infections with noroviruses can occur throughout the year. A seasonal increase in the number of infections can be observed especially in the cold season (October to March). A high number of unreported cases can be assumed Duration of contagiousness: During the acute illness and until at least 48 h after the clinical symptoms have subsided, affected persons are highly contagious. The virus is excreted for at least 7-14 days, in some cases even for weeks after the symptoms have subsided. Therefore, consistent hygiene measures must be observed even after the acute phase.

1. Hof H et al (2019):Hof H (2019) Special Virology. In: Hof H, Schlüter D, Dörries R, eds Duale Reihe Medizinische Mikrobiologie. 7th, completely revised and expanded edition. Stuttgart: Thieme p 204-206
2. Peñaflor-Téllez Y et al.(2019) Immune response modulation by caliciviruses. Front Immunol 10:2334.
3. Vinjé J et al. (2019) et al. ICTV Virus Taxonomy Profile: Caliciviridae. J Gen Virol 100:1469-1470.