Editing What is a norovirus? (section)

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<h3><span class="mw-headline">Classification</span></h3>
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<div class="thumbinner" style="width: 252px"><img class="thumbimage" height="219" alt="Transmission electron micrograph of Norovirus particles in faeces" width="250" border="0" src="http://upload.wikimedia.org/wikipedia/en/thumb/a/ae/Norovirus_4.jpg/250px-Norovirus_4.jpg" />
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<div class="magnify"><img height="11" alt="" width="15" src="/skins-1.5/common/images/magnify-clip.png" /></div>
Transmission electron micrograph of Norovirus particles in faeces</div>
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<p>Noroviruses (NoV) are a genetically diverse group of single stranded RNA, nonenveloped viruses belonging to the Caliciviridae family.<sup class="reference" id="cite_ref-health_24-0">[25]</sup> According to the International Committee on Taxonomy of Virus, the genus Norovirus has one species which is called &quot;Norwalk virus&quot; and assigned the abbreviation &quot;NV&quot;. Serotypes, strains and isolates include:<sup class="reference" id="cite_ref-species_0-1">[1]</sup></p>
<ul>
    <li>Desert Shield virus [U04469] (Hu/NLV/DSV395/1990/SR)</li>
    <li>Lordsdale virus [X86557] (Hu/NLV/LD/1993/UK)</li>
    <li>Mexico virus [U22498] (Hu/NLV/MX/1989/MX)</li>
    <li>Norwalk virus [M87661] (Hu/NLV/NV/1968/US)</li>
    <li>Hawaii virus [U07611] (Hu/NLV/HV/1971/US)</li>
    <li>Snow Mountain virus [L23831] (Hu/NLV/SMV/1976/US)</li>
    <li>Southampton virus [L07418] (Hu/NLV/SHV/1991/UK)</li>
</ul>
<p>Noroviruses are a major cause of acute gastroenteritis worldwide, often causing explosive outbreaks in institutions. They are highly contagious, with an inoculum of as few as ten particles being able to cause infection. Transmission occurs through ingesting contaminated food and water and by person-to-person spread. Transmission is predominantly faecal-oral but may be airborne due to aerosolisation of vomitus Noroviruses commonly isolated in cases of acute gastroenteritis belong to two genogroups: genogroup I (GI) includes Norwalk virus, Desert Shield virus and Southampton virus and II (GII) which includes Bristol virus, Lordsdale virus, Toronto virus, Mexico virus, Hawaii virus and Snow Mountain virus.<sup class="reference" id="cite_ref-health_24-1">[25]</sup></p>
<p>Noroviruses can genetically be classified into 5 different genogroups (GI, GII, GIII, GIV, and GV) which can be further divided into different genetic clusters or genotypes. For example genogroup II, the most prevalent human genogroup, presently contains 19 genotypes. Genogroups I, II and IV infect humans, whereas genogroup III infects bovine species and genogroup V has recently been isolated in mice.<sup class="reference" id="cite_ref-pmid17953996_25-0">[26]</sup></p>
<p>Noroviruses from Genogroup II, genotype 4 (abbreviated as GII.4) account for the majority of adult outbreaks of gastroenteritis and often sweep across the globe. Recent examples include US95/96-US strain, associated with global outbreaks in the mid- to late-90s, Farmington Hills virus associated with outbreaks in Europe and the United States in 2002 and in 2004 Hunter virus was associated with outbreaks in Europe, Japan and Australasia. In 2006 there was another large increase in NoV infection around the globe.<sup class="reference" id="cite_ref-pmid18177226_26-0">[27]</sup> In December, 2007 there was an outbreak at a country club in northern California where around 80-100 people were infected. Two new GII.4 variants caused around 80% of those Norovirus associated outbreaks and they have been termed 2006a and 2006b.<sup class="noprint Template-Fact"><span title="This claim needs references to reliable sources&nbsp;since January 2008" style="white-space: nowrap">[<i>citation needed</i>]</span></sup> Recent reports have shown a link between blood group and susceptibility to infection by norovirus.<sup class="reference" id="cite_ref-pmid12825167_27-0">[28]</sup><sup class="reference" id="cite_ref-pmid15890909_28-0">[29]</sup><sup class="reference" id="cite_ref-pmid15688291_29-0">[30]</sup></p>
<p>A study performed by scientists at Washington University School of Medicine in St. Louis, published in the journal PLoS Pathogens (July 18, 2008), suggests that the protein MDA-5 may be the primary immune sensor that detects the presence of noroviruses in the body.<sup class="reference" id="cite_ref-30">[31]</sup> Interestingly, some people have common variations of the MDA-5 gene that could make them more susceptible to norovirus infection.<sup class="reference" id="cite_ref-31">[32]</sup></p>
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