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| {{Swine influenza}} | | {{Swine influenza}} |
| {{CMG}} | | {{CMG}} |
| | ==Overview== |
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| == Classification == | | == Classification == |
| | Swine influenza may be classified according to the genera of the infective agent into either influenza A (common) or influenza C (rare). Influenza B has not been associated with development of swine influenza. |
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| SIV strains isolated to date have been classified either as [[Influenzavirus C]] or one of the various subtypes of the genus [[Influenzavirus A]].<ref>
| | ===Influenza A=== |
| {{cite journal
| | *Influenza A subtypes include the following: |
| |author=Heinen PP
| | :*H1N1 |
| |url=http://www.vetscite.org/publish/articles/000041/print.html
| | :*H1N2 |
| |title=Swine influenza: a zoonosis
| | :*H2N3 |
| |journal=Veterinary Sciences Tomorrow
| | :*H3N1 |
| |issn=1569-0830
| | :*H3N2 |
| |date=15 September 2003
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| |quote=Influenza B and C viruses are almost exclusively isolated from man, although influenza C virus has also been isolated from pigs and influenza B has recently been isolated from seals.
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| }}</ref>
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| === Influenza A ===
| | A new strain of H1N1, A/Veracruz/2009, emerged in 2009 and was responsible for the 2009 swine influenza outbreak in humans. |
| Swine influenza is known to be caused by influenza A subtypes [[H1N1]],<ref name = Iowa/> [[H1N2]],<ref name = Iowa>
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| {{cite web
| | ===Influenza C=== |
| |url=http://www.vetmed.iastate.edu/departments/vdpam/swine/diseases/chest/swineinfluenza/
| | *Influenza C has been described in a few case reports in the USA and Japan. |
| |work=Swine Diseases (Chest)
| | *Influenza C is not thought to be genetically diverse, and accordingly it has not been associated with outbreaks among humans. |
| |title=Swine Influenza
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| |publisher=Iowa State University College of Veterinary Medicine
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| }}</ref> [[H3N1]],<ref>
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| {{cite journal
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| |author=Shin JY, Song MS, Lee EH, Lee YM, Kim SY, Kim HK, Choi JK, Kim CJ, Webby RJ, Choi YK
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| |year=2006
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| |title=Isolation and characterization of novel H3N1 swine influenza viruses from pigs with respiratory diseases in Korea
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| |journal=Journal of Clinical Microbiology
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| |volume=44
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| |issue=11
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| |pages=3923–7
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| |doi=10.1128/JCM.00904-06
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| |pmid=16928961
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| }}</ref> [[H3N2]],<ref name = Iowa/> and H2N3.<ref>
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| {{cite journal
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| |title=Identification of H2N3 influenza A viruses from swine in the United States
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| |author=Ma W, Vincent AL, Gramer MR, Brockwell CB, Lager KM, Janke BH, Gauger PC, Patnayak DP, Webby RJ, Richt JA
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| |url=http://www.pnas.org/content/104/52/20949.full
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| |journal=Proc Nat Acad Sci U S A
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| |doi=10.1073/pnas.0710286104
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| |volume=104
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| |issue=52
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| |pages=20949–54
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| |pmid=18093945
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| |pmc=2409247
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| |date=26 December 2007
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| }}</ref>
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| In swine, three influenza A virus subtypes (H1N1, H3N2, and H1N2) are circulating throughout the world. In the United States, the H1N1 subtype was exclusively prevalent among swine populations before 1998; however, since late August 1998, H3N2 subtypes have been isolated from pigs. As of 2004, H3N2 virus isolates in US swine and turkey stocks were triple reassortants, containing genes from [[Human flu|human]] (HA, NA, and PB1), swine (NS, NP, and M), and [[Avian influenza|avian]] (PB2 and PA) lineages.<ref>
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| {{cite journal
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| |title=Interspecies and intraspecies transmission of triple reassortant H3N2 influenza A viruses | |
| |author=Yassine HM, Al-Natour MQ, Lee CW, Saif YM
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| |journal=Virol J
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| |year=2007
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| |month=November
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| |volume=28
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| |issue=4
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| |pages=129
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| |pmid=18045494
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| |pmc=2228287
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| |doi=10.1186/1743-422X-4-129
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| }}</ref>
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| === Interaction With H5N1 ===
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| Avian influenza virus [[H3N2]] is [[Endemic (epidemiology)|endemic]] in pigs in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains.<ref>
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| {{cite journal
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| |url=http://jcm.asm.org/cgi/content/full/46/3/1067?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=phylogenetic&searchid=1&FIRSTINDEX=230&resourcetype=HWFIG
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| |title=Genetic evolution of swine influenza A (H3N2) viruses in China from 1970 to 2006
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| |journal=Journal of Clinical Microbiology
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| |volume=46
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| |issue=3
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| |pages=1067
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| |year=2008
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| |month=March
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| |doi=10.1128/JCM.01257-07
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| |author=Yu, H.
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| |pmid=18199784
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| }}</ref> Health experts say pigs can carry human [[influenza]] viruses, which can combine (i.e. exchange homologous genome sub-units by genetic reassortment) with [[H5N1]], passing [[gene]]s and mutating into a form which can pass easily among humans.<ref>
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| {{cite web
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| |url=http://www.dh.gov.uk/en/Aboutus/MinistersandDepartmentLeaders/ChiefMedicalOfficer/Features/DH_4102997
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| |title=Bird flu and pandemic influenza: what are the risks?
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| |publisher=UK Department of Health
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| }}</ref> [[H3N2]] evolved from [[H2N2]] by [[antigenic shift]].<ref>
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| {{cite journal
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| |title=Genetic analysis of human H2N2 and early H3N2 influenza viruses, 1957–1972: evidence for genetic divergence and multiple reassortment events
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| |author=Lindstrom Stephen E, Cox Nancy J, Klimov Alexander
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| |journal=Virology
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| |volume=328
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| |issue=1
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| |date=15 October 2004
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| |pages=101–19
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| |doi=10.1016/j.virol.2004.06.009
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| |pmid=15380362
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| }}</ref> In August 2004, researchers in China found [[H5N1]] in pigs.<ref name="timeline">
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| {{cite web
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| |url=http://www.who.int/csr/disease/avian_influenza/Timeline_28_10a.pdf
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| |format=PDF
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| |title=H5N1 avian influenza: timeline
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| |author=World Health Organization
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| |date=28 October 2005
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| }}</ref>
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| ==References== | | ==References== |