Norovirus

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Norovirus
Transmission electron micrograph of noroviruses. The bar = 50 nm
Transmission electron micrograph of noroviruses. The bar = 50 nm
Virus classification
Group: Group IV ((+)ssRNA)
Family: Caliciviridae
Genus: Norovirus

Norovirus is an RNA virus of the Caliciviridae taxonomic family. This virus causes approximately 90% of epidemic non-bacterial outbreaks of gastroenteritis around the world,[1] and may be responsible for 50% of all foodborne outbreaks of gastroenteritis in the US.[2][3] Norovirus affects people of all ages. The viruses are transmitted by faecally contaminated food or water and by person-to-person contact.[4]

After infection, immunity to norovirus is usually incomplete and temporary.[5] There is an inherited predisposition to infection, and individuals with blood type O are more often infected,[1][6] while blood types B and AB can confer partial protection against symptomatic infection.[7][8]

Outbreaks of norovirus infection often occur in closed or semi-closed communities, such as long-term care facilities, hospitals, prisons, dormitories, and cruise ships where once the virus has been introduced, the infection spreads very rapidly by either person-to-person transmission or through contaminated food.[9] Many norovirus outbreaks have been traced to food that was handled by one infected person.[10]

Norovirus is rapidly inactivated by chlorine-based disinfectants, but because the virus particle does not have a lipid envelope, it is less susceptible to alcohols and detergents.[11]

There are different genogroups of norovirus and most noroviruses that infect humans are classified into genogroup G1 and G2.[12]

Contents

[edit] History

The norovirus was originally called the Norwalk Virus. The name was shortened to the norovirus after receiving national attention for being identified in multiple cruise ship outbreaks. The Norwalk Virus was named after Norwalk, Ohio, where an outbreak of acute gastroenteritis occurred among a vast majority of children at Bronson Elementary School in November 1968. In 1972, immune electron microscopy on stored stool samples identified a virus, which was given the name Norwalk virus. Numerous outbreaks with similar symptoms have been reported since. The cloning and sequencing of the Norwalk virus genome showed that these viruses have a genomic organization consistent with viruses belonging to the family Caliciviridae.[13] The name norovirus (Norovirus for the genus) was approved by the International Committee on Taxonomy of Viruses in 2002.[14]

Common names of the illness caused by noroviruses are winter vomiting disease, viral gastroenteritis and acute non-bacterial gastroenteritis,[4] also colloquially known as "stomach flu" — a broad name that can also refer to gastric inflammation caused by other viruses and bacteria.

The virus has previously been called Norwalk virus, Norwalk-like virus, SRSVs (Small Round Structured Viruses), and Snow Mountain virus.[15]

[edit] Signs and symptoms

The disease is usually self-limiting, and characterised by nausea, vomiting, diarrhea, and abdominal pain; and in some cases, loss of taste. General lethargy, weakness, muscle aches, headache, and low-grade fever may occur. Symptoms may persist for several days and may become life-threatening in the young, the elderly, and the immune-compromised if dehydration is ignored or not treated.[4] When a person becomes infected with norovirus, the virus begins to multiply within the small intestine. After approximately 1 to 2 days, norovirus symptoms can appear.

[edit] Diagnosis

Specific diagnosis of norovirus is routinely made by polymerase chain reaction (PCR) assays or real-time PCR assays, which give results within a few hours. These assays are very sensitive and can detect concentrations as low as 10 virus particles.[16]

Tests such as ELISA that use antibodies against a mixture of norovirus strains are available commercially but lack specificity and sensitivity.[17]

[edit] Epidemiology, prevention and infection control

Norovirus is extremely infectious, and without special precautions, each person with gastroenteritis will infect on average another 14 other people.[18]

Hand washing remains an effective method to reduce the spread of norovirus pathogens. Norovirus can be aerosolized when those stricken with the illness vomit. Surface sanitizing is recommended in areas where the Norovirus may be present on surfaces.

In health care environments, the prevention of nosocomial infections involves routine and terminal cleaning. Nonflammable alcohol vapor in CO2 systems are used in health care environments where medical electronics would be adversely affected by aerosolized chlorine or other caustic compounds.[19]

Ligocyte announced in 2007 that it was working on a vaccine and had started phase 1 trials.[20]

[edit] Associated food

Noroviruses are transmitted directly via person to person or indirectly via contaminated water and food. A CDC study of eleven outbreaks in New York State lists the suspected mode of transmission as person-to-person in seven outbreaks, foodborne in two, waterborne in one, and one unknown. The source of waterborne outbreaks may include water from municipal supplies, wells, recreational lakes, swimming pools and ice machines.[21]

Shellfish and salad ingredients are the foods most often implicated in Norwalk outbreaks. Ingestion of raw or insufficiently steamed clams and oysters poses a high risk for infection with the Norwalk virus. Foods other than shellfish are contaminated by ill food handlers.[22]

[edit] Course of disease and complication

Norovirus causes acute gastroenteritis that develops between 24 and 48 hours after exposure with a median of 33–36 hours, and lasts for 24–60 hours.[3] Severe illness is rare: although people are frequently treated in emergency rooms/Accident & Emergency, they are rarely admitted to the hospital. The number of deaths from norovirus in the US is estimated to be around 300 each year, with most of these occurring in the very young, elderly and persons with weakened immune systems.

The most common genotype identified in hospitalized children was GII.4 and increased amount of virus (7.2 x 107) were shed by those children. Even though GII.4 Norovirus was the most common identified, other genotypes were identified in less proportion, including the novel GII.18-NICA.[citation needed]

[edit] Detection of norovirus in foods

Routine protocols to detect norovirus (norovirus RNA) in clams and oysters by RT-PCR (reverse transcription polymerase chain reaction) are being employed by governmental laboratories such as the FDA in the USA. However, routine methods to detect the virus on other food items are not readily available due to the variable nature of different food items affecting concentration and extraction of the virus and presence of factors that make PCR (Polymerase chain reaction) analysis techniques ineffective.[23]

[edit] Microbiology

[edit] Classification

Transmission electron micrograph of Norovirus particles in faeces

Noroviruses (NoV) are a genetically diverse group of single stranded RNA, nonenveloped viruses belonging to the Caliciviridae family.[24] According to the International Committee on Taxonomy of Virus, the genus Norovirus has one species which is called "Norwalk virus" and assigned the abbreviation "NV". Serotypes, strains and isolates include:[25]

  • Desert Shield virus [U04469] (Hu/NLV/DSV395/1990/SR)
  • Lordsdale virus [X86557] (Hu/NLV/LD/1993/UK)
  • Mexico virus [U22498] (Hu/NLV/MX/1989/MX)
  • Norwalk virus [M87661] (Hu/NLV/NV/1968/US)
  • Hawaii virus [U07611] (Hu/NLV/HV/1971/US)
  • Snow Mountain virus [L23831] (Hu/NLV/SMV/1976/US)
  • Southampton virus [L07418] (Hu/NLV/SHV/1991/UK)

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 vomit. 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.[24]

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.[26]

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.[27] 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.[citation needed] Recent reports have shown a link between blood group and susceptibility to infection by norovirus.[28][29][30]

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.[31] Interestingly, some people have common variations of the MDA-5 gene that could make them more susceptible to norovirus infection.[32]

[edit] Virus structure

Noroviruses contain a positive-sense RNA genome of approximately 7.5 knt, encoding a major structural protein (VP1) of about 58~60 kDa and a minor capsid protein (VP2).[33] The virus particles demonstrate an amorphous surface structure when visualized using electron microscopy and are between 27-38 nm in size.[34]

[edit] Notable outbreaks

  • In November 2006, 679 (17%) out of 3,970 passengers and crew members aboard the trans-Atlantic Carnival Cruise Lines' Carnival Liberty, one of the world's largest cruise ships, contracted the virus. [35]
  • In the winter of 2007/08, an estimated three million people in the United Kingdom contracted "winter vomiting disease" (a popular name for the virus), with double the number of reported cases in England and Wales compared to the previous year. About 100 hospital wards were closed due to contamination.[36]
  • In October 2008, over 210 students and 2 staff members at Georgetown University contracted the virus.[37][38][39]
  • Also in October 2008, at least 275 students and 1 faculty member at the University of Southern California contracted the virus.[40][41]
  • Hope College, a small liberal-arts school located in Holland, Michigan, had to close its campus for five days in the fall of 2008 because of a serious Norovirus outbreak that infected over 500 students.[42]
  • Babson College, a business school closed its campus from March 28, 2009 until April 1, 2009 due to an outbreak of norovirus. More than 100 students were reported to be affected by the virus, but an estimated 300 cases were unreported. [43]

[edit] References

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  17. ^ Wilhelmi de Cal I, Revilla A, del Alamo JM, Román E, Moreno S, Sánchez-Fauquier A (2007). "Evaluation of two commercial enzyme immunoassays for the detection of norovirus in faecal samples from hospitalised children with sporadic acute gastroenteritis". Clin. Microbiol. Infect. 13 (3): 341–3. doi:10.1111/j.1469-0691.2006.01594.x. PMID 17391396. http://www.blackwell-synergy.com/openurl?genre=article&sid=nlm:pubmed&issn=1198-743X&date=2007&volume=13&issue=3&spage=341. 
  18. ^ Heijne JCM, Teunis P, Morroy G, et al. (2009). "Enhanced hygiene measures and norovirus transmission during an outbreak". Emerg. Infect. Dis. 15 (1): 24–30. doi:10.3201/1501.080299. http://www.cdc.gov/EID/content/15/1/pdfs/24.pdf. 
  19. ^ Chadwick PR, Beards G, Brown D, Caul EO, Cheesbrough J, Clarke I, Curry A, O'Brien S, Quigley K, Sellwood J, Westmoreland D (2000). "Management of hospital outbreaks of gastro-enteritis due to small roundstructured viruses". J. Hosp. Infect. 45 (1): 1–10. doi:10.1053/jhin.2000.0662. PMID 10833336. http://linkinghub.elsevier.com/retrieve/pii/jhin.2000.0662. 
  20. ^ http://www.ligocyte.com/downloads/Noro.pdf Norovirus candidate vaccine from Ligocyte
  21. ^ Hedberg CW, Osterholm MT (1993). "Outbreaks of food-borne and waterborne viral gastroenteritis". Clin. Microbiol. Rev. 6 (3): 199–210. PMID 8395330. http://cmr.asm.org/cgi/pmidlookup?view=long&pmid=8395330. 
  22. ^ Parashar UD, Monroe SS (2001). ""Norwalk-like viruses" as a cause of foodborne disease outbreaks". Rev. Med. Virol. 11 (4): 243–52. doi:10.1002/rmv.321. PMID 11479930. 
  23. ^ Shieh Y, Monroe SS, Fankhauser RL, Langlois GW, Burkhardt W, Baric RS (2000). "Detection of norwalk-like virus in shellfish implicated in illness". J. Infect. Dis. 181 Suppl 2: S360–6. doi:10.1086/315578. PMID 10804149. http://www.journals.uchicago.edu/cgi-bin/resolve?JID990682. 
  24. ^ a b Department of Health and Ageing Norovirus laboratory case definition
  25. ^ Schuffenecker I, Ando T, Thouvenot D, Lina B, Aymard M (2001). "Genetic classification of "Sapporo-like viruses"". Arch. Virol. 146 (11): 2115–32. doi:10.1007/s007050170024. PMID 11765915. http://link.springer.de/link/service/journals/00705/bibs/1146011/11462115.htm. Retrieved on 2009-03-01. 
  26. ^ Ramirez S, Giammanco GM, De Grazia S, Colomba C, Martella V, Arista S (2008). "Genotyping of GII.4 and GIIb norovirus RT-PCR amplicons by RFLP analysis". J. Virol. Methods 147 (2): 250–6. doi:10.1016/j.jviromet.2007.09.005. PMID 17953996. http://linkinghub.elsevier.com/retrieve/pii/S0166-0934(07)00362-X. 
  27. ^ Tu ET, Bull RA, Greening GE, Hewitt J, Lyon MJ, Marshall JA, McIver CJ, Rawlinson WD, White PA (2008). "Epidemics of gastroenteritis during 2006 were associated with the spread of norovirus GII.4 variants 2006a and 2006b" ([dead link] – Scholar search). Clin. Infect. Dis. 46 (3): 413–20. doi:10.1086/525259. PMID 18177226. http://bjr.birjournals.org/cgi/pmidlookup?view=long&pmid=18177226. 
  28. ^ Huang P, Farkas T, Marionneau S, Zhong W, Ruvoën-Clouet N, Morrow AL, Altaye M, Pickering LK, Newburg DS, LePendu J, Jiang X (2003). "Noroviruses bind to human ABO, Lewis, and secretor histo-blood group antigens: identification of 4 distinct strain-specific patterns". J. Infect. Dis. 188 (1): 19–31. doi:10.1086/375742. PMID 12825167. http://www.journals.uchicago.edu/cgi-bin/resolve?JID30248. 
  29. ^ Huang P, Farkas T, Zhong W, Tan M, Thornton S, Morrow AL, Jiang X (2005). "Norovirus and histo-blood group antigens: demonstration of a wide spectrum of strain specificities and classification of two major binding groups among multiple binding patterns". J. Virol. 79 (11): 6714–22. doi:10.1128/JVI.79.11.6714-6722.2005. PMID 15890909. http://jvi.asm.org/cgi/pmidlookup?view=long&pmid=15890909. 
  30. ^ Rockx BH, Vennema H, Hoebe CJ, Duizer E, Koopmans MP (2005). "Association of histo-blood group antigens and susceptibility to norovirus infections". J. Infect. Dis. 191 (5): 749–54. doi:10.1086/427779. PMID 15688291. http://www.journals.uchicago.edu/cgi-bin/resolve?JID33169. 
  31. ^ McCartney SA, Thackray LB, Gitlin L, Gilfillan S, Virgin Iv HW, Colonna M (July 18 2008). "MDA-5 recognition of a murine norovirus.". PLoS Pathog. PMID 18636103. 
  32. ^ Researchers Discover Primary Sensor That Detects Stomach Viruses Newswise, Retrieved on July 20, 2008.
  33. ^ Clarke IN, Lambden PR (2000). "Organization and expression of calicivirus genes". J. Infect. Dis. 181 Suppl 2: S309–16. doi:10.1086/315575. PMID 10804143. http://www.journals.uchicago.edu/cgi-bin/resolve?JID990679. 
  34. ^ Prasad BV, Crawford S, Lawton JA, Pesavento J, Hardy M, Estes MK (2001). "Structural studies on gastroenteritis viruses". Novartis Found. Symp. 238: 26–37; discussion 37–46. doi:10.1002/0470846534.ch3. PMID 11444031. 
  35. ^ "Investigation Update on the Carnival Liberty". Centers for Disease Control and Prevention (CDC). United States Department of Health and Human Services. 25 November 2006. http://www.cdc.gov/nceh/vsp/surv/outbreak/2006/nov13carnivalliberty.htm. 
  36. ^ "Vomiting bug 'hits three million'". BBC News. 2008-01-11. http://news.bbc.co.uk/1/hi/health/7182988.stm. Retrieved on 2008-09-09. 
  37. ^ "Leo’s food sickens 96". The Georgetown Voice. 2008-10-02. http://www.georgetownvoice.com/2008-10-02/news/leo-s-food-sickens-96. Retrieved on 2008-10-02. 
  38. ^ "Contagious Virus May Have Caused Outbreak". The Hoya. 2008-10-02. http://www.thehoya.com/node/16583. Retrieved on 2008-10-02. 
  39. ^ "Nearly 100 Georgetown Students Sickened by Possible Food-Borne Illness". NBC4. 2008-10-01. http://www.nbc4.com/health/17598556/detail.html. Retrieved on 2008-10-02. 
  40. ^ "Southern California Hit by Norovirus". U.S. News & World Report. 2008-10-06. http://www.usnews.com/blogs/paper-trail/2008/10/06/southern-california-hit-by-norovirus.html. Retrieved on 2008-10-06. 
  41. ^ "USC News Update: Contagious Gastrointestinal Virus". Update. 2008-10-07. http://www.usc.edu/uscnews/stories/15715.html. Retrieved on 2008-10-07. 
  42. ^ Presidential Update Winter 2009
  43. ^ "Babson Health Advisory". http://www3.babson.edu/healthadvisory/. 

Look - Cain Donaghey got this virus for 3 days - and recovered.

[edit] External links

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