CALICIVIRIDAE FAMILY

Caliciviridae family is a family of non-enveloped viruses that possess a ss(+)RNA genome. Their site of replication is in the cytoplasm, and viruses in this family have an icosahedral nucleocapsid. They measure between 27-40 nm in diameter. Viruses in the Caliciviridae family are generally called caliciviruses. Members of the calciviruses cause viral gastroenteritis in humans. Caliciviridae family comprises of four genera of viruses; and these are Vesivirus, Lagovirus, Norovirus and Sapovirus genera. Only Norovirus and Sapovirus genera contain viruses that cause infections in humans. Vesivirus and Lagovirus contain viruses that cause infections in other mammals including pigs, rabbits and cats. Norwalk virus (NV) and Sapporo virus (SV) are the two important members of the genera Norovirus and Sapovirus respectively; and they both cause epidemic gastroenteritis in humans. NV and SV have a worldwide distribution, and they are transmitted in human population via the feacal-oral route.

Together with adenoviruses and rotaviruses, caliciviruses are the most frequently reported viral agents that cause gastroenteritis in human populations. Gastroenteritis caused by NV and SV occurs in both children and adults. And infections with NV are mostly common in overcrowded settings such as in military camps and nursing homes. Human infections due to Noroviruses are usually associated with the consumption of fresh or raw foods such as salads and sandwiches during outdoor activities or camping. Noroviruses enter the human body predominantly via the oral route. Transmission of NV from person-to-person and via contaminated water or food is also possible. The clinical symptoms of the disease include vomiting, anorexia, abdominal cramp, fever, myalgias, chills, diarrhea, sore throat, headache and nausea.

Noroviruses causes prolonged gastroenteritis in immunocompromised patients as opposed to individuals with active or strong immunity that can contain the infection to some extent. Generally, viral gastroenteritis due to NV can be benign and self-limiting especially at the covert stage of the disease; and thus most cases of the infection are not treated with antivirals due to non-complications of the disease. However, NV infection can be very debilitating when the disease is at its symptomatic stage. Oral administration of bismuth subsalicylate and other oral rehydration therapy (O.R.T) is vital to contain the disease at its symptomatic stage. Regular hand washing and proper disposal of sewage (so that they do not contaminate the water ways) as well as good environmental and personal hygiene are important for the control and prevention of gastroenteritis due to caliciviruses. No vaccine exists for the vaccination of human population against NV infection.

SELECTED REFERENCES

Acheson N.H (2011). Fundamentals of Molecular Virology. Second edition. John Wiley and Sons Limited, West Sussex, United Kingdom.

Ahmad K (2002). Norwalk-like virus attacks troops in Afghanistan. Lancet Infect Dis, 2:391.

Alan J. Cann (2005). Principles of Molecular Virology. 4th edition. Elsevier Academic Press,   Burlington, MA, USA.

Alba R, Bosch A and Chillon M (2005). Gutless adenovirus: last-generation adenovirus for gene therapy. Gene Ther, Suppl 12:S18-S27.

Alberts B, Bray D, Johnson A, Lewis J, Raff M, Roberts K and Walter P (1998). Essential Cell Biology: An Introduction to the Molecular Biology of the Cell. Third edition. Garland Publishing Inc., New York.

Balows A, Hausler W, Herrmann K.L, Isenberg H.D and Shadomy H.J (1991). Manual of clinical microbiology. 5th ed. American Society of Microbiology Press, USA.

Barrett   J.T (1998).  Microbiology and Immunology Concepts.  Philadelphia,   PA: Lippincott-Raven Publishers. USA.

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