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What Are Noroviruses?

written by: Ollie Hicks•edited by: Paul Arnold•updated: 11/30/2009

The norovirus genus is responsible for many outbreaks of gastroenteritis worldwide. In this article I take a look at the structure and evolution of the different norovirus strains, and norovirus infection, treatment and prevention.

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    What Is The Norovirus?

    What is the Norovirus or group of noroviruses? The first norovirus discovered was the Norwalk virus in 1968, named for the location of the first identified outbreak. There are many strains of the norovirus genus of viruses, subdivided into five genogroups. All of them belong to the Caliciviridae family of viruses. A variety of other names for the norovirus are in use, e.g. winter vomiting bug, or simply - stomach bugs.

    The norovirus is an uncoated single-stranded round positive-sense RNA virus, under 40 nanometres in size. Very small amounts can lead to an infection. Samples can be amplified by reverse-transcriptase polymerase chain reaction (cloning the original sample) to enable the identification of a norovirus infection.

    Geographically gastroenteritis as a result of bacterial infection tends to pose a more serious challenge in economically deprived countries with less stringent public hygiene and healthcare, but viral gastroenteritis is similarly prevalent in both westernized and less affluent countries. [1]

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    Norovirus Transmission and Infection

    Transmission electron micrograph of Norwalk virus - image released into the public domain by US Federal Govt. You may pick up a norovirus infection from faecally tainted food or water, vomitus spray or physical contact with an infected individual, as so little infective material is required. Norovirus infections are extremely prevalent: norovirus is implicated in the vast majority of cases of gastroenteritis. Rates of more than 90% of multiple viral gastroenteritis reports have been quoted as being due to noroviruses in the USA.[1]

    Norovirus Gastroenteritis

    Some research suggests that cell membrane-attached carbohydrates provide the site of attachment that the norovirus grabs on to in an infection. These carbohydrates may be associated with certain blood-groups, explaining why some sections of the population are more susceptible than others to the norovirus family, e.g. according to blood type.[1] The virus tends to be ingested orally, survives a bath in stomach acid and attacks the gastroenteric lining.

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    Norovirus Symptoms

    Infection with norovirus produces the symptoms of gastroenteritis, including nausea, sickness and diarrhoea. Infected individuals have been observed to develop lesions in the gastroenteric tract, leading to poor absorption of nutrients. Gastroenteritis resulting from a norovirus is often mild in healthy individuals but there are a small percentage of fatalities in susceptible or weakened individuals e.g. the elderly or the already sick.

    Norovirus Infection Treatments

    Formal treatment may not be required in a mild case, but if dehydration results then intravenous fluids may be administered. Neither anti-diarrheal drugs nor antibiotics are useful for viral infection.

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    Prevention and Control of Norovirus Infection

    Prevention as well as treatment of the norovirus should be considered. Application of disinfectants can be effective in killing the virus but the lack of a lipid membrane means that methods used to break a lipid membrane down e.g. detergents, are ineffective.

    Gastroenteritis and its attendant symptoms may be an inevitable part of life occasionally, but good prevention techniques, personal hygiene, and containment of outbreaks can at least minimize any inconvenience and illness.

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    1. Fauci, A.S., Braunwald, E., Kasper, D.L & Hauser, S.L. "Harrison's Principles of Internal Medicine", 17th edn., pp. 1204-1207. USA: The McGraw-Hill Companies, Inc., 2008.

    2. Cook, G.C. & Zumla, A.I. “Manson's Tropical Diseases.", pp. 821-822. China: Saunders Ltd., 2008.

    3. Jay, J.M., Loessner, M.J., Golden, D.A. “Modern Food Microbiology.", p.730. USA: Springer Science+Business Media, Inc., 2005.

    4. Bennett, J.V. & Jarvis, W.R. “Bennett & Brachman's Hospital Infections.", p. 327. Philadelphia: Lipincott Williams & Wilkins, 2007.