Introduction

Welcome to the calicivirus family web page! My name is Emily Chen, and I am a senior majoring in human biology at Stanford University. I made this web page for a class, Humans & Viruses, taught by Dr. Robert Siegel. My classmates and I are making web pages for most of the 20 human virus families, as a resource for anyone looking for information on viruses.

Historical notes

Members of the calicivirus family have long been known to cause pathogenesis in animals, but only recently have caliciviruses been recognized as a human virus taxon. The Norwalk virus, which caused an outbreak of gastroenteritis in Norwalk, Ohio, was identified as a "small round-structured virus" in 1972, but it was not until sequencing of the genome in 1991 that it was identified as a member of the calicivirus family. Hepatitis E virus was also recognized as a calicivirus in 1991 after sequencing of its genome.

Classification and Taxonomy

Caliciviruses derive their name from the Latin word for calix, or cup. Members of the calicivirus family have 32 distinct, cup-shaped surface depressions that give it a unique appearance. (Click here to see an electron mircrograph image of caliciviruses.)

Properties of Caliciviruses
ssRNA, positive sense, infectious, linear, monopartite genome
nonenveloped, icosahedral capsid, spherical in shape
replication occurs in the cytoplasm
virions are released through lysis of the infected cell
transmitted by respiration or ingestion

Not all members of the calicivirus family have the cup-shaped surface depressions. Caliciviruses may be divided according to morphology:
1. "typical" caliciviruses, which have the cup-shaped surface depressions. e.g., hepatitis E virus (HEV)
2. "amorphous small round-structured viruses" e.g., Norwalk agent, Snow Mountain agent, Otofuke/Hawaii agent.

Human Diseases associated with this family

Gastroenteritis - the "typical" caliciviruses are associated with gastroenteritis in infants while the Norwalk virus group is more often associated with gastroenteritis in adults and children.
There is typically a short incubation period (1-2 days) with calicivirus-caused gastroenteritis. Typical signs and symptoms include nausea, vomiting, diarrhea, abdominal pain, and a low fever. Headache and myalgia may also be present. Symptoms usually do not last longer than 3 days. There is no evidence of chronic infection or chronic gastroenteritis damage following infection. Acquired immunity to the Norwalk virus is usually poor; patients reinfected twice in 2 years became sick during the second infection. Acquired immunity to the typical caliciviruses, however, is usually strong; antibody to the typical infection acquired early in life protects adults.

Hepatitis E - this disease is found mostly in less developed countries, and produces a clinical infection primarily in 15-40 year olds; it affects children subclinically. HEV has an incubation period of 2-8 weeks (typically 5-6 weeks) and results in symptoms similar to hepatitis A: malaise, lethargy, anorexia, nausea, and vomiting, followed by dark urine, pale stools, and jaundice. In contrast to hepatitis A, however, cholestasis is the most prominent feature of hepatitis E. One unexplained feature of hepatits E pathogenesis, however, is that it affects pregnant women much more severely; the mortality rate for pregnant women is 10-20% while the overall mortality rate is 0.5-3%.

Transmission

Caliciviruses are transmitted via the fecal-oral or the respiratory route. Transmission of HEV is usually through contaminated water.

Epidemiology

Outbreaks of gastroenteritis are usually attributed to fecal contamination of food or water (e.g., consumption of raw or undercooked shellfish that were harvested from contaminated water) and discharge of sewage into drinking water supplies or recreational water areas. Secondary spread between groups in close contact, such as within a household or school, is common.
HEV is an important cause of hepatitis in Asia; the most well-known case was in New Delhi in 1955, when 29,000 cases of acute hepatitis was reported. During epidemics, 1-10% of people are typically affected.

Management and Prevention

Endemic gastroenteritis can be controlled with high levels of sanitation and personal hygiene, and clean water supply. Significant resources and national commitment are necessary to achieve this, which it makes it more difficult for less developed countries to control endemic gastroenteritis.
Outbreaks of hepatitis E can be controlled with chlorinated water and improved sanitation levels. During epidemics, food and water should be handled especially carefully; water should be boiled, and food should be completely cooked or peeled.

Vaccination

Passive immunization is not effective against HEV. Vaccines against calicivirus-caused gastroenteritis and hepatitis E have not been developed.

Useful web links

The Calicivirus Pages at the Institute of Animal Health (UK) - Calicivirus news, labs that study calicivirus, links to other calicivirus pages, and more.

Virology web site created by the Garry Lab.

Virus-related stuff on Dr. Siegel's web page.

References

Belshe, Robert B. Textbook of Human Virology. Mosby Year Book, 1991. pp. 10, 816-818.

Siegel, Robert D. Humans and Viruses Course Reader. Human Biology 115A, Stanford University, 1998.

White, David O. and Fenner, Frank J. Medical Virology, Fourth Edition. Academic Press, 1994, pp. 406-417

Created: February 1, 1998
Last modified: March 8, 1998