Editing Norovirus (section)

=== Classification ===
Noroviruses (NoV) are a genetically diverse group of single-stranded [[positive-sense RNA]], non-[[virus envelope|enveloped]] viruses belonging to the family ''[[Caliciviridae]]''.<ref name=ICTV>{{Cite web|url=http://www.ictv.global/report/caliciviridae|title=Family: Caliciviridae &#124; ICTV|website=www.ictv.global|access-date=2019-10-02|archive-date=2021-08-29|archive-url=https://web.archive.org/web/20210829153617/https://talk.ictvonline.org/ictv-reports/ictv_online_report/positive-sense-rna-viruses/w/caliciviridae|url-status=live}}</ref><ref name=health>{{cite web |last1=Public Health Laboratory Network |title=Norovirus Laboratory Case Definition (LCD) |url=http://www.health.gov.au/internet/main/publishing.nsf/Content/cda-phlncd-norwalk.htm |publisher=Australian Government Department of Health and Ageing |language=en |date=25 September 2006 |access-date=15 September 2020 |archive-date=1 May 2008 |archive-url=https://web.archive.org/web/20080501230732/http://www.health.gov.au/internet/main/publishing.nsf/Content/cda-phlncd-norwalk.htm |url-status=live }}</ref> According to the [[International Committee on Taxonomy of Viruses]], the genus ''Norovirus'' has one species: Norwalk virus (''Norovirus norwalkense'').<ref name=ICTV/><ref name=ictvhistory />

Noroviruses can genetically be classified into at least seven different genogroups (GI, GII, GIII, GIV, GV, GVI, and GVII), which can be further divided into other genetic clusters or [[genotype]]s.<ref>{{cite journal |last1=Atmar |first1=Robert L |last2=Baehner |first2=Frank |last3=Cramer |first3=Jakob P |last4=Lloyd |first4=Eric |last5=Sherwood |first5=James |last6=Borkowski |first6=Astrid |last7=Mendelman |first7=Paul M |last8=Al-Ibrahim |first8=Mohamed S |last9=Bernstein |first9=David L |last10=Brandon |first10=Donald M |last11=Chu |first11=Laurence |last12=Davis |first12=Matthew G |last13=Epstein |first13=Robert J |last14=Frey |first14=Sharon E |last15=Rosen |first15=Jeffrey B |last16=Treanor |first16=John J |title=Persistence of Antibodies to 2 Virus-Like Particle Norovirus Vaccine Candidate Formulations in Healthy Adults: 1-Year Follow-up With Memory Probe Vaccination |journal=The Journal of Infectious Diseases |date=15 August 2019 |volume=220 |issue=4 |pages=603–614 |doi=10.1093/infdis/jiz170|pmid=31001633 }}</ref>

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.<ref name=health/>

Most noroviruses that infect humans belong to genogroups GI and GII.<ref name="pmid10752550">{{cite journal | vauthors = Vinjé J, Green J, Lewis DC, Gallimore CI, Brown DW, Koopmans MP | title = Genetic polymorphism across regions of the three open reading frames of "Norwalk-like viruses" | journal = Arch. Virol. | volume = 145 | issue = 2 | pages = 223–41 | year = 2000 | pmid = 10752550 | doi = 10.1007/s007050050020 | s2cid = 20525287 }}</ref>
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.<ref>{{cite journal |vauthors=Noel JS, Fankhauser RL, Ando T, Monroe SS, Glass RI | title = Identification of a distinct common strain of "Norwalk-like viruses" having a global distribution | journal = J. Infect. Dis. | volume = 179 | issue = 6 | pages = 1334–44 | year = 2000 | pmid = 10228052 | doi = 10.1086/314783 | doi-access = free }}</ref>

Recent examples include US95/96-US strain, associated with global outbreaks in the mid- to late-1990s; [[Farmington Hills]] virus associated with outbreaks in Europe and the United States in 2002 and in 2004; and Hunter virus which was associated with outbreaks in Europe, Japan, and Australasia. In 2006, there was another large increase in NoV infection around the globe.<ref name="pmid18177226">{{cite journal |vauthors=Tu ET, Bull RA, Greening GE, Hewitt J, Lyon MJ, Marshall JA, McIver CJ, Rawlinson WD, White PA | title = Epidemics of gastroenteritis during 2006 were associated with the spread of norovirus GII.4 variants 2006a and 2006b | journal = Clin. Infect. Dis. | volume = 46 | issue = 3 | pages = 413–20 | year = 2008 | pmid = 18177226 | doi = 10.1086/525259 | s2cid = 27972379 | doi-access =  }}</ref> Reports have shown a link between the expression of human histo-[[blood group antigen]]s (HBGAs) and the susceptibility to norovirus infection. Studies have suggested the [[capsid]] of noroviruses may have evolved from [[selective pressure]] of human HBGAs.<ref name="pmid21519121">{{cite journal | author = Shirato H | title = Norovirus and histo-blood group antigens | journal = Japanese Journal of Infectious Diseases | volume = 64 | issue = 2 | pages = 95–103 | year = 2011 | doi = 10.7883/yoken.64.95 | pmid = 21519121 | doi-access = free }}</ref> HBGAs are not, however, the receptor or facilitator of norovirus infection. Co-factors such as [[bile salts]] may facilitate the infection, making it more intense when introduced during or after the initial infection of the host tissue.<ref name=":0">{{Cite journal|last1=Graziano|first1=Vincent R.|last2=Wei|first2=Jin|last3=Wilen|first3=Craig B.|date=30 May 2019|title=Norovirus Attachment and Entry|journal=Viruses|language=en|volume=11|issue=6|pages=495|doi=10.3390/v11060495|pmid=31151248|pmc=6630345|doi-access=free}}</ref> Bile salts are produced by the liver in response to eating fatty foods, and they help with the absorption of consumed [[lipid|lipids]]. It is not yet clear at what specific point in the Norovirus replication cycle bile salts facilitate infection: penetration, uncoating, or maintaining capsid stability.<ref name=":0" />

The protein [[IFIH1|MDA-5]] may be the primary immune sensor that detects the presence of noroviruses in the body.<ref>{{cite journal | vauthors = McCartney SA, Thackray LB, Gitlin L, Gilfillan S, Virgin HW, Virgin Iv HW, Colonna M | title = MDA-5 Recognition of a Murine Norovirus | journal = PLOS Pathog | volume = 4 | issue = 7 | page = e1000108 | date = July 18, 2008 | pmid = 18636103 | pmc = 2443291 | doi = 10.1371/journal.ppat.1000108 | veditors = Baric RS | doi-access = free }}</ref>  Some people have common variations of the MDA-5 gene that could make them more susceptible to norovirus infection.<ref>[http://newswise.com/articles/view/542714/ Researchers Discover Primary Sensor That Detects Stomach Viruses] {{Webarchive|url=https://web.archive.org/web/20090202094714/http://newswise.com/articles/view/542714/ |date=2009-02-02 }} Newswise, Retrieved on July 20, 2008.</ref>