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{{About|influenza viruses in pigs|the 2009 outbreak|2009 flu pandemic|the 2009 human virus|Pandemic H1N1/09 virus}}
{{Flu}}
[[Image:H1N1 influenza virus.jpg|thumb|upright|[[Electron microscope]] image of the [[reassortment|reassorted]] H1N1 influenza virus photographed at the CDC Influenza Laboratory. The viruses are 80–120&nbsp;[[nanometre]]s in diameter.<ref>{{cite web|author= International Committee on onomy of Viruses |title=The Universal Virus Database, version 4: Influenza A |url=http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.046.0.01.htm}}{{dead link|date=May 2011}}</ref>]]

'''Swine influenza''', also called '''pig influenza''', '''swine flu''', '''hog flu''' and '''pig flu''', is an infection by any one of several types of swine influenza [[virus]]es. '''Swine influenza virus''' ('''SIV''') or '''swine-origin influenza virus''' ('''S-OIV''' ) is any strain of the [[Orthomyxoviridae|influenza family of viruses]] that is [[endemism|endemic]] in [[pig]]s.<ref name=Merck>{{Cite journal
|url=http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/121407.htm
|title=Swine influenza|journal=The Merck Veterinary Manual
|year=2008|accessdate=April 30, 2009
|isbn=1442167424}}</ref> As of 2009, the known SIV strains include [[Influenzavirus C|influenza C]] and the subtypes of [[Influenza A Virus|influenza A]] known as [[H1N1]], [[H1N2]], H2N1, [[H3N1]], [[H3N2]], and [[H2N3]].

Swine influenza virus is common throughout pig populations worldwide. Transmission of the virus from pigs to humans is not common and does not always lead to [[human flu]], often resulting only in the production of [[antibody|antibodies]] in the blood. If transmission does cause human flu, it is called [[zoonosis|zoonotic]] swine flu. People with regular exposure to pigs are at increased risk of swine flu infection.

During the mid-20th century, identification of influenza subtypes became possible, allowing accurate diagnosis of transmission to humans. Since then, only 50 such transmissions have been confirmed. These strains of swine flu rarely pass from human to human. Symptoms of zoonotic swine flu in humans are similar to those of [[influenza]] and of [[influenza-like illness]] in general, namely [[chills]], [[fever]], [[pharyngitis|sore throat]], [[myalgia|muscle pains]], severe [[headache]], [[cough]]ing, [[fatigue (medical)|weakness]] and [[malaise|general discomfort]].

In August 2010, the [[World Health Organization]] declared the swine flu [[pandemic]] officially over.<ref>[http://abclocal.go.com/kabc/story?section=news/health&id=7602267 ]{{dead link|date=May 2011}}</ref>

==Classification==
Of the three [[genera]] of influenza viruses that cause [[human flu]], two also cause influenza in pigs, with [[Influenzavirus A|influenza A]] being common in pigs and [[Influenzavirus C|influenza C]] being rare.<ref>{{Cite journal
|author=Heinen PP
|url=http://www.vetscite.org/publish/articles/000041/print.html
|title=Swine influenza: a zoonosis
|journal=Veterinary Sciences Tomorrow
|issn=1569-0830
|date=15 September 2003
|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.
}}</ref> [[Influenzavirus B|Influenza B]] has not been reported in pigs. Within influenza A and influenza C, the strains found in pigs and humans are largely distinct, although because of [[reassortment]] there have been transfers of genes among strains crossing swine, avian, and human species boundaries.

===Influenza C===
Influenza viruses infect both humans and pigs, but do not infect birds.<ref name=Bouvier>{{Cite journal|author=Bouvier NM, Palese P |title=THE BIOLOGY OF INFLUENZA VIRUSES |journal=Vaccine |volume=26 Suppl 4 |pages=D49–53 |year=2008 |month=September |pmid=19230160 |doi=10.1016/j.vaccine.2008.07.039|pmc=3074182|issue=Suppl 4}}</ref> Transmission between pigs and humans have occurred in the past.<ref>{{Cite journal|author=Kimura H |title=Interspecies transmission of influenza C virus between humans and pigs |journal=Virus Research |volume=48 |issue=1 |pages=71–9 |year=1997 |month=April |pmid=9140195 |doi=10.1016/S0168-1702(96)01427-X|author-separator=,|author2=Abiko C|author3=Peng G|display-authors=3|last4=Muraki|first4=Yasushi|last5=Sugawara|first5=Kanetsu|last6=Hongo|first6=Seiji|last7=Kitame|first7=Fumio|last8=Mizuta|first8=Katsumi|last9=Numazaki|first9=Yoshio}}</ref> For example, influenza C caused small outbreaks of a mild form of influenza amongst children in Japan<ref name=Matsuzaki>{{Cite journal|author=Matsuzaki Y |title=Antigenic and Genetic Characterization of Influenza C Viruses Which Caused Two Outbreaks in Yamagata City, Japan, in 1996 and 1998 |journal=Journal of Clinical Microbiology |volume=40 |issue=2 |pages=422–9 |year=2002 |month=February |pmid=11825952 |pmc=153379 |doi=10.1128/JCM.40.2.422-429.2002|author-separator=,|author2=Sugawara K|author3=Mizuta K|display-authors=3|last4=Tsuchiya|first4=E.|last5=Muraki|first5=Y.|last6=Hongo|first6=S.|last7=Suzuki|first7=H.|last8=Nakamura|first8=K.}}</ref> and California.<ref name=Matsuzaki/> Because of its limited host range and the lack of genetic diversity in influenza C, this form of influenza does not cause pandemics in humans.<ref name=Lynch>{{Cite journal|author=Lynch JP, Walsh EE |title=Influenza: evolving strategies in treatment and prevention |journal=Semin Respir Crit Care Med |volume=28 |issue=2 |pages=144–58 |year=2007 |month=April |pmid=17458769 |doi=10.1055/s-2007-976487}}</ref>

===Influenza A===
Swine influenza is known to be caused by influenza A subtypes [[H1N1]],<ref name = Iowa>
{{cite web
|url=http://www.vetmed.iastate.edu/departments/vdpam/swine/diseases/chest/swineinfluenza/
|work=Swine Diseases (Chest)
|title=Swine Influenza
|publisher=[[Iowa State University]] College of Veterinary Medicine
}}</ref> [[H1N2]],<ref name = Iowa /> [[H2N3]],<ref>{{Cite journal|author=Ma W |title=Identification of H2N3 influenza A viruses from swine in the United States |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=104 |issue=52 |pages=20949–54 |year=2007 |month=December |pmid=18093945 |pmc=2409247 |doi=10.1073/pnas.0710286104|author-separator=,|author2=Vincent AL|author3=Gramer MR|display-authors=3|last4=Brockwell|first4=C. B.|last5=Lager|first5=K. M.|last6=Janke|first6=B. H.|last7=Gauger|first7=P. C.|last8=Patnayak|first8=D. P.|last9=Webby|first9=R. J.}}</ref> [[H3N1]],<ref>{{Cite journal|author=Shin JY |title=Isolation and Characterization of Novel H3N1 Swine Influenza Viruses from Pigs with Respiratory Diseases in Korea |journal=Journal of Clinical Microbiology |volume=44 |issue=11 |pages=3923–7 |year=2006 |month=November |pmid=16928961 |pmc=1698339 |doi=10.1128/JCM.00904-06|author-separator=,|author2=Song MS|author3=Lee EH|display-authors=3|last4=Lee|first4=Y.-M.|last5=Kim|first5=S.-Y.|last6=Kim|first6=H. K.|last7=Choi|first7=J.-K.|last8=Kim|first8=C.-J.|last9=Webby|first9=R. J.}}</ref> and [[H3N2]].<ref name = Iowa/> In pigs, three influenza A virus subtypes (H1N1, H1N2, and H3N2) are the most common strains worldwide.<ref name=Kothalawala/> 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 [[Reassortment|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>{{Cite journal|author=Yassine HM, Al-Natour MQ, Lee CW, Saif YM |title=Interspecies and intraspecies transmission of triple reassortant H3N2 influenza A viruses |journal=Virology Journal |volume=4 |issue= |page=129 |year=2007 |pmid=18045494 |pmc=2228287 |doi=10.1186/1743-422X-4-129}}</ref>

===Surveillance===
Although there is no formal national surveillance system in the United States to determine what viruses are circulating in pigs,<ref name="MMWR5815a5">
{{Cite journal
|url=http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5815a5.htm
|title=Swine influenza A (H1N1) infection in two children --- Southern California, March--April 2009
|date=22 April 2009
|publisher=[[Centers for Disease Control]]
|work=Morbidity and Mortality Weekly Report
|volume=58 (Dispatch)
|issue=1–3
|author1=<Please add first missing authors to populate metadata.>
}}</ref> an informal surveillance network in the United States is part of a world surveillance network.

A [[Veterinary pathologist|veterinary medical pathologist]], Tracey McNamara, set up a national disease surveillance system in zoos because the zoos do active disease surveillance and many of the exotic animals housed there have broad susceptibilities. Many species fall below the radar of any federal agencies (including dogs, cats, pet [[prairie dogs]], zoo animals, and urban wildlife), even though they may be important in the early detection of human disease outbreaks.<ref>{{cite web
|url=http://www.homelandsecurity.org/journal/Default.aspx?oid=15&ocat=4
|title=Interview With Tracey McNamara
|publisher=Journal of Homeland Security, August 2002
|accessdate=2009-05-26
}}</ref>
<ref>{{cite web
|url=http://thebulletin.org/web-edition/columnists/laura-h-kahn/animals-the-worlds-best-and-cheapest-biosenso
|title=Animals: The world's best (and cheapest) biosensors
|author=Laura H. Kahn
|date=2007-03-13
|accessdate=2005-05-26
}}</ref>

==History==
Swine influenza was first proposed to be a disease related to human flu during the [[1918 flu pandemic]], when pigs became really sick at the same time as humans.<ref name=Knobler>{{Cite book|editor=Knobler S, Mack A, Mahmoud A, Lemon S |title=The Threat of Pandemic Influenza: Are We Ready? Workshop Summary (2005) |chapter=1: The Story of Influenza |page=75 |chapterurl=http://books.nap.edu/openbook.php?isbn=0309095042&page=75 |publisher=The National Academies Press |location=Washington, D.C.}}</ref> The first identification of an influenza virus as a cause of disease in pigs occurred about ten years later, in 1930.<ref name="pmid12034486" /> For the following 60 years, swine influenza strains were almost exclusively H1N1. Then, between 1997 and 2002, new strains of three different subtypes and five different genotypes emerged as causes of influenza among pigs in North America. In 1997–1998, [[H3N2]] strains emerged. These strains, which include genes derived by [[reassortment]] from human, swine and avian viruses, have become a major cause of swine influenza in North America. Reassortment between H1N1 and [[H3N2]] produced [[H1N2]]. In 1999 in Canada, a strain of [[H4N6]] crossed the species barrier from birds to pigs, but was contained on a single farm.<ref name="pmid12034486">{{Cite journal
| author = Olsen CW
| title = The emergence of novel swine influenza viruses in North America
| journal = Virus Research
| volume = 85
| issue = 2
| pages = 199–210
| year = 2002
| month = May
| pmid = 12034486
| doi =10.1016/S0168-1702(02)00027-8
| url = http://linkinghub.elsevier.com/retrieve/pii/S0168170202000278
| issn =
}}</ref>

The H1N1 form of swine flu is one of the descendants of the strain that caused the [[1918 flu pandemic]].<ref name=NYT76>{{Cite news|url=http://select.nytimes.com/gst/abstract.html?res=F10914FA3E5E14768FDDAC0894D1405B868BF1D3&scp=9&sq=Swine+Flu+epidemic&st=p |title=Soft evidence and hard sell |publisher=New York Times |date=5 September 1976 | first=Philip M. | last=Boffey}}</ref><ref name=Pandemic/> As well as persisting in pigs, the descendants of the 1918 virus have also circulated in humans through the 20th century, contributing to the normal seasonal epidemics of influenza.<ref name=Pandemic/> However, direct transmission from pigs to humans is rare, with only 12 recorded cases in the U.S. since 2005.<ref>{{Cite news|url=http://www.reuters.com/article/latestCrisis/idUSN26488473 |title=U.S. pork groups urge hog farmers to reduce flu risk |agency=Reuters |date=26 April 2009}}</ref> Nevertheless, the retention of influenza strains in pigs after these strains have disappeared from the human population might make pigs a reservoir where influenza viruses could persist, later emerging to reinfect humans once human immunity to these strains has waned.<ref name=Heinen2003>{{Cite journal
| title = Swine influenza: a zoonosis
| url = http://www.vetscite.org/publish/articles/000041/print.html
| year = 2003
| author = Heinen, P.
| journal = Veterinary Sciences Tomorrow
| pages = 1–11
| accessdate = 2009-05-04
}}</ref>

Swine flu has been reported numerous times as a [[zoonosis]] in humans, usually with limited distribution, rarely with a widespread distribution. Outbreaks in swine are common and cause significant economic losses in industry, primarily by causing stunting and extended time to market. For example, this disease costs the British meat industry about £65 million every year.<ref>{{Cite journal|doi=10.1136/vr.135.9.199|author=Kay RM, Done SH, Paton DJ |title=Effect of sequential porcine reproductive and respiratory syndrome and swine influenza on the growth and performance of finishing pigs |journal=Vet. Rec. |volume=135 |issue=9 |pages=199–204 |year=1994 |month=August |pmid=7998380}}</ref>

===1918 pandemic in humans===
The [[1918 flu pandemic]] in humans was associated with H1N1 and influenza appearing in pigs;<ref name=Pandemic>
{{Cite journal
|author=Taubenberger JK, Morens DM
|journal=Emerg Infect Dis
|year=2006
|url=http://www.cdc.gov/ncidod/eid/vol12no01/05-0979.htm
|pmid=16494711
|title=1918 Influenza: the mother of all pandemics
|volume=12
|issue=1
|pages=15–22
}}</ref> this may reflect a zoonosis either from swine to humans, or from humans to swine. Although it is not certain in which direction the virus was transferred, some evidence suggests, in this case, pigs caught the disease from humans.<ref name=Knobler/> For instance, swine influenza was only noted as a new disease of pigs in 1918, after the first large outbreaks of influenza amongst people.<ref name=Knobler/> Although a recent [[Phylogeny|phylogenetic]] analysis of more recent strains of influenza in humans, birds, and swine suggests the 1918 outbreak in humans followed a reassortment event within a mammal,<ref name="pmid18353690">{{Cite journal
| author = Vana G, Westover KM
| title = Origin of the 1918 Spanish influenza virus: a comparative genomic analysis
| journal = Molecular Phylogenetics and Evolution
| volume = 47
| issue = 3
| pages = 1100–10
| year = 2008
| month = June
| pmid = 18353690
| doi = 10.1016/j.ympev.2008.02.003
| url =
| issn =
}}</ref> the exact origin of the 1918 strain remains elusive.<ref>{{Cite journal|author=Antonovics J, Hood ME, Baker CH |title=Molecular virology: was the 1918 flu avian in origin? |journal=Nature |volume=440 |issue=7088 |pages=E9; discussion E9–10 |year=2006 |month=April |pmid=16641950 |doi=10.1038/nature04824}}</ref> It is estimated that anywhere from 50 to 100&nbsp;million people were killed worldwide.<ref name=Pandemic/><ref>{{Cite journal|author=Patterson KD, Pyle GF |title=The geography and mortality of the 1918 influenza pandemic |journal=Bulletin of the History of Medicine |volume=65 |issue=1 |pages=4–21 |year=1991 |pmid=2021692}}</ref>

===1976 U.S. outbreak===<!-- some incoming links anchor here -->
{{Main|1976 swine flu outbreak}}
On February 5, 1976, a United States army recruit at [[Fort Dix]] said he felt tired and weak. He died the next day, and four of his fellow soldiers were later hospitalized. Two weeks after his death, health officials announced the cause of death was a new strain of swine flu. The strain, a variant of H1N1, is known as <!-- start -->A/New Jersey/1976 (H1N1)<!-- end -->. It was detected only from January 19 to February 9 and did not spread beyond Fort Dix.<ref name="Gaydos+2006">{{Cite journal
| author = Gaydos JC, Top FH, Hodder RA, Russell PK
| title = Swine influenza a outbreak, Fort Dix, New Jersey, 1976
| journal = Emerging Infectious Diseases
| volume = 12
| issue = 1
| pages = 23–8
| year = 2006
| month = January
| pmid = 16494712
| doi =
| url = http://www.cdc.gov/ncidod/EID/vol12no01/05-0965.htm
| issn =
}}</ref>

[[Image:FordSwineFluShot1.jpg|thumb|right|U.S. President Ford receives a swine flu vaccination]]
This new strain appeared to be closely related to the strain involved in the 1918 flu pandemic. Moreover, the ensuing increased surveillance uncovered another strain in circulation in the U.S.: [[H3N2|A/Victoria/75 (H3N2)]] spread simultaneously, also caused illness, and persisted until March.<ref name="Gaydos+2006"/> Alarmed public health officials decided action must be taken to head off another major pandemic, and urged President [[Gerald Ford]] that every person in the U.S. be vaccinated for the disease.<ref>{{Cite news|first=Harold M. |last=Schmeck |authorlink= |coauthors= |title=Ford Urges Flu Campaign To Inoculate Entire U.S. |url=http://select.nytimes.com/gst/abstract.html?res=F50A17FD3C5A167493C7AB1788D85F428785F9 |work=The New York Times |publisher= |date=March 25, 1976 |accessdate= }}</ref>

The [[vaccination]] program was plagued by delays and public relations problems.<ref>Richard E. Neustadt and Harvey V. Fineberg. (1978). [http://www.nap.edu/catalog.php?record_id=12660 The Swine Flu Affair: Decision-Making on a Slippery Disease]. ''National Academies Press''.</ref> On October 1, 1976, immunizations began, and three senior citizens died soon after receiving their injections. This resulted in a media outcry that linked these deaths to the immunizations, despite the lack of any proof the vaccine was the cause. According to science writer Patrick Di Justo, however, by the time the truth was known—that the deaths were not proven to be related to the vaccine—it was too late. "The government had long feared mass panic about swine flu—now they feared mass panic about the swine flu vaccinations." This became a strong setback to the program.<ref name=DiJusto>[http://www.salon.com/env/feature/2009/04/28/1976_swine_flu/ "The Last Great Swine Flu Epidemic"], ''Salon.com'', April 28, 2009.</ref>

There were reports of [[Guillain-Barré syndrome]], a paralyzing [[neuromuscular]] disorder, affecting some people who had received swine flu immunizations. Although if a link exists is still not clear, this syndrome may be a side effect of influenza vaccines. As a result, Di Justo writes, "the public refused to trust a government-operated health program that killed old people and crippled young people." In total, 48,161,019 Americans, or just over 22% of the population, had been immunized by the time the [[National Influenza Immunization Program]] was effectively halted on December 16, 1976.<ref>{{Cite journal|author=Retailliau HF, Curtis AC, Storr G, Caesar G, Eddins DL, Hattwick MA |title=Illness after influenza vaccination reported through a nationwide surveillance system, 1976-1977 |journal=American Journal of Epidemiology |volume=111 |issue=3 |pages=270–8 |year=1980 |month=March |pmid=7361749 |url=http://aje.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=7361749}}</ref>
<ref>{{cite web|url=http://www.census.gov/popest/archives/1990s/popclockest.txt|title=Historical National Population Estimates: July 1, 1900 to July 1, 1999|date=2000-06-28|publisher=Population Division, [[U.S. Census Bureau|U.S. Bureau of the Census]]|location=[[Washington D.C.]]|accessdate=2009-08-21}}</ref>

Overall, there were 1098 cases of Guillain-Barré Syndrome (GBS) recorded nationwide by CDC surveillance, 532 of which occurred after vaccination and 543 before vaccination.<ref>{{Cite journal|author=Schonberger LB |title=Guillain-Barre syndrome following vaccination in the National Influenza Immunization Program, United States, 1976--1977 |journal=American Journal of Epidemiology |volume=110 |issue=2 |pages=105–23 |year=1979 |month=August |pmid=463869 |url=http://aje.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=463869|author-separator=,|author2=Bregman DJ|author3=Sullivan-Bolyai JZ|display-authors=3|last4=Keenlyside|first4=RA|last5=Ziegler|first5=DW|last6=Retailliau|first6=HF|last7=Eddins|first7=DL|last8=Bryan|first8=JA}}</ref> About one to two cases per 100,000 people of GBS occur every year, whether or not people have been vaccinated.<ref name=CDCGBS/> The vaccination program seems to have increased this normal risk of developing GBS by about to one extra case per 100,000 vaccinations.<ref name=CDCGBS>{{cite web|url=http://www.cdc.gov/h1n1flu/vaccination/gbs_qa.htm |title=General Questions and Answers on Guillain-Barr syndrome |publisher=Centers for Disease Control and Prevention |date=September 14, 2009}}</ref>

Recompensation charges were filed for over 4000 cases of severe vaccination damage, including 25 deaths, totalling US$ 3.5 billion, by 1979.<ref>{{cite web|url=http://articles.latimes.com/2009/apr/27/science/sci-swine-history27 |title=Swine Flu 1976 &#124; Swine flu 'debacle' of 1976 is recalled - Los Angeles Times |publisher=Articles.latimes.com |date=2009-04-27 |accessdate=2011-08-17}}</ref><ref>{{cite web|url=http://www.wanttoknow.info/health/1976_swine_flu_vaccine_60_minutes_transcript |title=Swine Flu Vaccine: 1976 CBS '60 Minutes' Transcript |publisher=Wanttoknow.info |date=1979-11-04 |accessdate=2011-08-17}}</ref>

The CDC stated most studies on modern influenza vaccines have seen no link with GBS,<ref name=CDCGBS/><ref>{{Cite journal|author=Haber P, Sejvar J, Mikaeloff Y, DeStefano F |title=Vaccines and Guillain-Barré syndrome |journal=Drug Safety |volume=32 |issue=4 |pages=309–23 |year=2009 |pmid=19388722 |doi=10.2165/00002018-200932040-00005}}</ref><ref>{{Cite journal|author=Kaplan JE, Katona P, Hurwitz ES, Schonberger LB |title=Guillain-Barré syndrome in the United States, 1979-1980 and 1980-1981. Lack of an association with influenza vaccination |journal=JAMA |volume=248 |issue=6 |pages=698–700 |year=1982 |month=August |pmid=7097920 |doi=10.1001/jama.248.6.698}}</ref> Although one review gives an incidence of about one case per million vaccinations,<ref>{{Cite journal|author=Vellozzi C, Burwen DR, Dobardzic A, Ball R, Walton K, Haber P |title=Safety of trivalent inactivated influenza vaccines in adults: Background for pandemic influenza vaccine safety monitoring |journal=Vaccine |volume=27 |issue=15 |pages=2114–2120 |year=2009 |month=March |pmid=19356614 |doi=10.1016/j.vaccine.2009.01.125}}</ref> a large study in China, reported in the [[NEJM]], covering close to 100 million doses of H1N1 flu vaccine, found only 11 cases of Guillain-Barre syndrome, which is lower than the normal rate of the disease in China; "The risk-benefit ratio, which is what vaccines and everything in medicine is about, is overwhelmingly in favor of vaccination."<ref>{{cite web|url=http://www.wunderground.com/DisplayHealthDay.asp?id=649531 |title=Last Year's (2009) H1N1 Flu Vaccine Was Safe, Study Finds |publisher=Wunderground.com |date=2011-02-02 |accessdate=2011-05-22}}</ref>

===1988 zoonosis===
In September 1988, a swine flu virus killed one woman and infected others. A 32-year old woman, Barbara Ann Wieners, was eight months pregnant when she and her husband, Ed, became ill after visiting the hog barn at a county fair in [[Walworth County, Wisconsin]]. Barbara died eight days later, after developing pneumonia.<ref name="pmid2153372">{{Cite journal|author=McKinney WP, Volkert P, Kaufman J |title=Fatal swine influenza pneumonia during late pregnancy |journal=Archives of Internal Medicine |volume=150 |issue=1 |pages=213–5 |year=1990 |month=January |pmid=2153372 |doi=10.1001/archinte.150.1.213}}</ref> The only pathogen identified was an H1N1 strain of swine influenza virus.<ref name="pmid9511782">{{Cite journal|author=Kimura K, Adlakha A, Simon PM |title=Fatal case of swine influenza virus in an immunocompetent host |journal=Mayo Clinic Proceedings. Mayo Clinic |volume=73 |issue=3 |pages=243–5 |year=1998 |month=March |pmid=9511782 |doi=10.4065/73.3.243}}</ref> Doctors were able to induce labor and deliver a healthy daughter before she died. Her husband recovered from his symptoms.

Influenza-like illness (ILI) was reportedly widespread among the pigs exhibited at the fair. Of the 25 swine exhibitors aged 9 to 19 at the fair, 19 tested positive for antibodies to SIV, but no serious illnesses were seen. The virus was able to spread between people, since one to three health care personnel who had cared for the pregnant woman developed mild, influenza-like illnesses, and antibody tests suggested they had been infected with swine flu, but there was no community outbreak.<ref>{{cite web|url=http://www.cdc.gov/swineflu/key_facts.htm |title=Key Facts About Swine Flu (CDC) |publisher=Cdc.gov |date= |accessdate=2009-05-07}}</ref><ref name="pmid1845913">{{Cite journal|author=Wells DL |title=Swine influenza virus infections. Transmission from ill pigs to humans at a Wisconsin agricultural fair and subsequent probable person-to-person transmission |journal=JAMA |volume=265 |issue=4 |pages=478–81 |year=1991 |pmid=1845913 |doi=10.1001/jama.265.4.478|author-separator=,|author2=Hopfensperger DJ|author3=Arden NH|display-authors=3|last4=Harmon|first4=MW|last5=Davis|first5=JP|last6=Tipple|first6=MA|last7=Schonberger|first7=LB}}</ref>

===1998 US outbreak in swine===
In 1998, swine flu was found in pigs in four U.S. states. Within a year, it had spread through pig populations across the United States. Scientists found this virus had originated in pigs as a recombinant form of flu strains from birds and humans. This outbreak confirmed that pigs can serve as a crucible where novel influenza viruses emerge as a result of the reassortment of genes from different strains.<ref>{{Cite journal| author=Stephanie Desmon | url=http://www.baltimoresun.com/news/health/bal-swine-flu-strain0428,0,3165467.story | title=Expert: Swine flu virus more complex than typically seen | journal=Baltimore Sun | date=April 28, 2009 | format=}} {{Dead link|date=March 2010}}</ref><ref>{{cite web|url=http://www.newscientist.com/blogs/shortsharpscience/2009/04/why-the-pork-industry-hates-th.html |title=Pork industry is blurring the science of swine flu - Short Sharp Science |publisher=New Scientist |date= |accessdate=2009-05-07}}</ref><ref>{{cite web|url=http://www.newscientist.com/article/mg20227063.800-swine-flu-the-predictable-pandemic.html?full=true |title=Swine flu: The predictable pandemic? - 29 April 2009 |publisher=New Scientist |date= |accessdate=2009-05-07}}</ref> Genetic components of these 1998 triple-hybrid stains would later form six out of the eight viral gene segments in the 2009 flu outbreak.<ref name="hsus.org">[http://www.hsus.org/farm/news/ournews/swine_flu_virus_origin_1998_042909.html CDC Confirms Ties to Virus First Discovered in U.S. Pig Factories]{{dead link|date=May 2011}}</ref><ref name="hsus.org2">[http://www.hsus.org/farm/resources/pubs/swine_flu.html Video Segments 3,4,5 in Flu Factories: Tracing the Origins of the Swine Flu Pandemic]{{dead link|date=May 2011}}</ref><ref name="video.hsus.org3">[http://video.hsus.org/index.jsp?fr_story=6d7c34894aab86190765da51973379a3438f294b Swine Flu Kept Stable Humans Untouched For 80 Years]{{dead link|date=May 2011}}</ref><ref name="video.hsus.org">[http://video.hsus.org/index.jsp?fr_story=6f816594cf08612a30048e72b5058afe4aeed401 Triple Hybrid Mutant Pig-Bird-Human Crossbreed Virus ]{{dead link|date=May 2011}}</ref><ref name="North Carolina, 1998 Ground Zero">[http://video.hsus.org/index.jsp?fr_story=a89aa9c8dee6d32ec3dd828fe295222733cc1837 North Carolina, 1998 Ground Zero]{{dead link|date=May 2011}}</ref>

===2007 Philippine outbreak in swine===
{{Expand section|date=April 2009}}<!-- explain connection (if any) between swine flu outbreak and hog cholera -->
On August 20, 2007, the Department of Agriculture<!--Unclear.. Does this mean the Philippines Dept of Agriculture or some other country? --> officers investigated the outbreak ([[epizootic]]) of swine flu in [[Nueva Ecija]] and central [[Luzon]], Philippines. The mortality rate is less than 10% for swine flu, unless there are complications like [[hog cholera]]. On July 27, 2007, the Philippine National Meat Inspection Service (NMIS) raised a hog cholera "red alert" warning over [[Metro Manila]] and five regions of Luzon after the disease spread to backyard pig farms in [[Bulacan]] and [[Pampanga]], even if these tested negative for the swine flu virus.<ref>
{{Cite news
|url=http://www.gmanews.tv/story/56805/DA-probes-reported-swine-flu-outbreak-in-N-Ecija
|title=DA probes reported swine flu 'outbreak' in N. Ecija
|publisher=Gmanews.tv
|date=
|accessdate=2009-04-25
}}</ref><ref>
{{Cite news
|url=http://www.gmanews.tv/story/53014/Govt-declares-hog-cholera-alert-in-Luzon
|title=Gov't declares hog cholera alert in Luzon
|publisher=Gmanews.tv
|date=
|accessdate=2009-04-25}}</ref>

===2009 Northern Ireland outbreak in swine===
Since November 2009, 14 deaths as a result of swine flu in Northern Ireland have been reported. The majority of the victims were reported to have pre-existing health conditions which had lowered their immunity. This closely corresponds to the 19 patients who had died in the year prior due to swine flu, where 18 of the 19 were determined to have lowered immune systems. Because of this, many mothers whom have just given birth are strongly encouraged to get a flu shot because their immune systems are vulnerable. Also, studies have shown that people between the ages of 15 and 44 have the highest rate of infection. Although most people now recover, having any conditions that lower one's immune system increases the risk of having the flu become potentially lethal. In Northern Ireland now, approximately 56% of all people under 65 who are entitled to the vaccine have gotten the shot, and the outbreak is said to be under control.<ref>
{{Cite news
|url=http://www.bbc.co.uk/news/uk-northern-ireland-12149164
|title=New mothers urged to get swine flu vaccine
|publisher=BBC News
|date=2011-01-10
|accessdate=2011-01-20
}}</ref>

==H1N1 virus pandemic history==
A study conducted in 2011, and published in the journal Nature, has managed to establish the evolutionary origin of the flu strain of swine origin (S-OIV).<ref>{{cite web|author=|url=http://www.nature.com/nature/journal/v459/n7250/full/nature08182.html |title=Origins and evolutionary genomics of the 2009 swine-origin H1N1 influenza A epidemic : Article |publisher=Nature |date= |accessdate=2011-08-17}}</ref>

The phylogenetic origin of the flu virus that caused the 2009 pandemics can be traced before 1918. Around 1918, the ancestral virus, of avian origin, crossed the species boundaries and infected humans as human H1N1. The same phenomenon took place soon after in America, where the human virus was infecting pigs; it lead the emergence of the H1N1 swine strain, which later became the classic swine flu.

The new human H1N1 flu strain of avian origin kept transmitting among human populations until around 1957, when there was a co-infection between this strain and the avian H1N1 in humans. A reassortment event lead to the development of a new strain (H2N2). From this point onwards, no outbreaks of H1N1 were reported in humans until around 1976.

New events of reassortment were not reported until 1968, when the avian strain H1N1 infected humans again; this time the virus met the strain H2N2, and the reassortment originated the strain H3N2. This strain has remained as a stable flu strain until now.

The mid-1970s were important for the evolution of flu strains. First, the re-emergence of the human H1N1 strain became a seasonal strain. Then, a small outbreak of swine H1N1 occurred in humans, and finally, the human H2N2 strain apparently became extinct. Around 1979, the avian H1N1 strain infected pigs and gave rise to Euroasiatic swine flu and H1N1 Euroasiatic swine virus, which is still being transmitted in swine populations.

The critical moment for the 2009 outbreak was between 1990 and 1993. A triple reassortment event in a pig host of North American H1N1 swine virus, the human H3N2 virus and avian H1N1 virus generated the swine H1N2 strain.
Finally, the last step in S-OIV history, was in 2009, when the virus H1N2 co-infected a human host at the same time as the Euroasiatic H1N1 swine strain. This led to the emergence of a new human H1N1 strain, which caused the 2009 pandemic.

On June 11, 2009, the World Health Organization raised the worldwide pandemic alert level to Phase 6 for swine flu which is the highest alert level.<ref name="Choffnes, Eileen R. 2010">Choffnes, Eileen R., Alison Mack, and David A. Relman. The Domestic and International Impacts of the 2009-H1N1 Influenza a Pandemic: Global Challenges, Global Solutions : Workshop Summary. Washington, D.C.: National Academies, 2010. Print.</ref> This alert level means that the swine flu had spread worldwide and there were cases of people with the virus in most countries. The pandemic level identifies the spread of the disease or virus and not necessarily the severity of the disease.

Swine flu spread very rapidly worldwide due to its high human to human transmission rate and due to the frequency of air travel.<ref name="Choffnes, Eileen R. 2010"/>

==Transmission==
===Transmission between pigs===
Influenza is quite common in pigs, with about half of breeding pigs having been exposed to the virus in the US.<ref name=cfsph/> Antibodies to the virus are also common in pigs in other countries.<ref name=cfsph/>

The main route of transmission is through direct contact between infected and uninfected animals.<ref name=Kothalawala/> These close contacts are particularly common during animal transport. [[Intensive farming]] may also increase the risk of transmission, as the pigs are raised in very close proximity to each other.<ref>{{Cite journal|author=Gilchrist MJ, Greko C, Wallinga DB, Beran GW, Riley DG, Thorne PS |title=The Potential Role of Concentrated Animal Feeding Operations in Infectious Disease Epidemics and Antibiotic Resistance |journal=Environmental Health Perspectives |volume=115 |issue=2 |pages=313–6 |year=2007 |month=February |pmid=17384785 |pmc=1817683 |doi=10.1289/ehp.8837}}</ref><ref>{{Cite journal|author=Saenz RA, Hethcote HW, Gray GC |title=Confined Animal Feeding Operations as Amplifiers of Influenza |journal=Vector Borne and Zoonotic Diseases |volume=6 |issue=4 |pages=338–46 |year=2006 |pmid=17187567 |pmc=2042988 |doi=10.1089/vbz.2006.6.338}}</ref> The direct transfer of the virus probably occurs either by pigs touching noses, or through dried mucus. Airborne transmission through the aerosols produced by pigs coughing or sneezing are also an important means of infection.<ref name=Kothalawala/> The virus usually spreads quickly through a herd, infecting all the pigs within just a few days.<ref name=Merck/> Transmission may also occur through wild animals, such as [[wild boar]], which can spread the disease between farms.<ref>{{Cite journal|author=Vicente J, León-Vizcaíno L, Gortázar C, José Cubero M, González M, Martín-Atance P |title=Antibodies to selected viral and bacterial pathogens in European wild boars from southcentral Spain |journal=Journal of Wildlife Diseases |volume=38 |issue=3 |pages=649–52 |year=2002 |month=July |pmid=12238391 |url=http://www.jwildlifedis.org/cgi/pmidlookup?view=long&pmid=12238391}}</ref>

===Transmission to humans===
People who work with poultry and swine, especially those with intense exposures, are at increased risk of [[zoonosis|zoonotic]] infection with influenza virus endemic in these animals, and constitute a population of human hosts in which [[zoonosis]] and [[reassortment]] can co-occur.<ref name="pmid19276439">{{Cite journal|author=Gray GC, Kayali G |title=Facing pandemic influenza threats: the importance of including poultry and swine workers in preparedness plans |journal=Poultry Science |volume=88 |issue=4 |pages=880–4 |year=2009 |month=April |pmid=19276439 |doi=10.3382/ps.2008-00335}}</ref> Vaccination of these workers against influenza and surveillance for new influenza strains among this population may therefore be an important public health measure.<ref>{{Cite journal|author=Gray GC, Trampel DW, Roth JA |title=Pandemic Influenza Planning: Shouldn't Swine and Poultry Workers Be Included? |journal=Vaccine |volume=25 |issue=22 |pages=4376–81 |year=2007 |month=May |pmid=17459539 |pmc=1939697 |doi=10.1016/j.vaccine.2007.03.036}}</ref> Transmission of influenza from swine to humans who work with swine was documented in a small surveillance study performed in 2004 at the University of Iowa.<ref name="pmid18258038">{{Cite journal|author=Gray GC, McCarthy T, Capuano AW, Setterquist SF, Olsen CW, Alavanja MC |title=Swine Workers and Swine Influenza Virus Infections |journal=Emerging Infectious Diseases |volume=13 |issue=12 |pages=1871–8 |year=2007 |month=December |pmid=18258038 |url=http://www.cdc.gov/eid/content/13/12/1871.htm |pmc=2876739}}</ref> This study, among others, forms the basis of a recommendation that people whose jobs involve handling poultry and swine be the focus of increased public health surveillance.<ref name="pmid19276439"/> Other professions at particular risk of infection are veterinarians and meat processing workers, although the risk of infection for both of these groups is lower than that of farm workers.<ref>{{Cite journal|author=Myers KP |title=Are Swine Workers in the United States at Increased Risk of Infection with Zoonotic Influenza Virus? |journal=Clinical Infectious Diseases |volume=42 |issue=1 |pages=14–20 |year=2006 |month=January |pmid=16323086 |pmc=1673212 |doi=10.1086/498977|author-separator=,|author2=Olsen CW|author3=Setterquist SF|display-authors=3|last4=Capuano|first4=A. W.|last5=Donham|first5=K. J.|last6=Thacker|first6=E. L.|last7=Merchant|first7=J. A.|last8=Gray|first8=G. C.}}</ref>

===Interaction with avian H5N1 in pigs===
Pigs are unusual as they can be infected with influenza strains that usually infect three different species: pigs, birds and humans.<ref name=Thacker>{{Cite journal|author=Thacker E, Janke B |title=Swine influenza virus: zoonotic potential and vaccination strategies for the control of avian and swine influenzas |journal=J. Infect. Dis. |volume=197 Suppl 1 |issue= |pages=S19–24 |year=2008 |month=February |pmid=18269323 |doi=10.1086/524988}}</ref> This makes pigs a host where influenza viruses might exchange genes, producing new and dangerous strains.<ref name=Thacker/> Avian influenza virus [[H3N2]] is [[Endemic (epidemiology)|endemic]] in [[pig]]s in China, and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains.<ref>{{Cite journal|author=Yu H |title=Genetic Evolution of Swine Influenza A (H3N2) Viruses in China from 1970 to 2006 |journal=Journal of Clinical Microbiology |volume=46 |issue=3 |pages=1067–75 |year=2008 |month=March |pmid=18199784 |pmc=2268354 |doi=10.1128/JCM.01257-07|author-separator=,|author2=Hua RH|author3=Zhang Q|display-authors=3|last4=Liu|first4=T.-Q.|last5=Liu|first5=H.-L.|last6=Li|first6=G.-X.|last7=Tong|first7=G.-Z.}}</ref> [[H3N2]] evolved from [[H2N2]] by [[antigenic shift]].<ref>{{Cite journal|author=Lindstrom SE, Cox NJ, Klimov A |title=Genetic analysis of human H2N2 and early H3N2 influenza viruses, 1957-1972: evidence for genetic divergence and multiple reassortment events |journal=Virology |volume=328 |issue=1 |pages=101–19 |year=2004 |month=October |pmid=15380362 |doi=10.1016/j.virol.2004.06.009}}</ref> In August 2004, researchers in China found [[H5N1]] in pigs.<ref name="timeline">
{{cite web
|url=http://www.who.int/csr/disease/avian_influenza/Timeline_28_10a.pdf
|format=PDF
|title=H5N1 avian influenza: timeline
|author=World Health Organization
|date=28 October 2005
}}</ref>
[[Image:Swine influenza symptoms on swine-en.svg|thumb|Main symptoms of swine flu in swine<ref name=Merck/>]]
These H5N1 infections may be quite common; in a survey of 10 apparently healthy pigs housed near poultry farms in [[West Java]], where avian flu had broken out, five of the pig samples contained the H5N1 virus. The Indonesian government has since found similar results in the same region. Additional tests of 150 pigs outside the area were negative.<ref>{{Cite news
|url=http://www.cidrap.umn.edu/cidrap/content/influenza/avianflu/news/may2705avflu.html
|publisher=Center for Infectious Disease Research and Policy
|place=University of Minnesota
|title=Indonesian pigs have avian flu virus; bird cases double in China
|date=27 May 2005
|accessdate=2009-04-26
}}</ref><ref>{{Cite news
|editor=Roos Robert
|url=http://www.cidrap.umn.edu/cidrap/content/influenza/avianflu/news/mar3109swine-jw.html
|title=H5N1 virus may be adapting to pigs in Indonesia
|publisher=Center for Infectious Disease Research & Policy
|place=University of Minnesota
|date=31 March 2009
|accessdate=2009-04-26
}} report on pigs as carriers.</ref>

==Signs and symptoms==
===In swine===
In pigs, influenza infection produces [[fever]], [[lethargy]], [[sneezing]], [[coughing]], [[Dyspnea|difficulty breathing]] and decreased appetite.<ref name=Kothalawala>{{Cite journal|author=Kothalawala H, Toussaint MJ, Gruys E |title=An overview of swine influenza |journal=Vet Q |volume=28 |issue=2 |pages=46–53 |year=2006 |month=June |pmid=16841566}}</ref> In some cases the infection can cause [[abortion]]. Although mortality is usually low (around 1–4%),<ref name=Merck/> the virus can produce [[weight loss]] and [[Growth failure|poor growth]], causing economic loss to farmers.<ref name=Kothalawala/> Infected pigs can lose up to 12&nbsp;pounds of body weight over a three to four week period.<ref name=Kothalawala/>

===In humans===
[[Image:PD Diagram of swine flu symptoms EN.svg|thumb|Main symptoms of swine flu in humans<ref>{{cite web|url=http://www.cdc.gov/swineflu/key_facts.htm|title=Centers for Disease Control and Prevention > Key Facts about Swine Influenza (Swine Flu)|accessdate=April 27, 2009}}</ref>]]

Direct transmission of a swine flu virus from pigs to humans is occasionally possible (called [[zoonosis|zoonotic]] swine flu). In all, 50 cases are known to have occurred since the first report in medical literature in 1958, which have resulted in a total of six deaths.<ref name="pmid17366454">{{Cite journal|author=Myers KP, Olsen CW, Gray GC |title=Cases of Swine Influenza in Humans: A Review of the Literature |journal=Clinical Infectious Diseases |volume=44 |issue=8 |pages=1084–8 |year=2007 |month=April |pmid=17366454 |pmc=1973337 |doi=10.1086/512813}}</ref> Of these six people, one was pregnant, one had [[leukemia]], one had [[Hodgkin's lymphoma]] and two were known to be previously healthy.<ref name="pmid17366454"/> Despite these apparently low numbers of infections, the true rate of infection may be higher, since most cases only cause a very mild disease, and will probably never be reported or diagnosed.<ref name="pmid17366454"/>
[[File:Video xo.ogv|thumb|In this video, Dr. Joe Bresee, with CDC's Influenza Division, describes the symptoms of swine flu and warning signs to look for that indicate the need for urgent medical attention. <br /> See also: See this video with subtitles on YouTube <ref>{{cite web|url=http://www.youtube.com/watch?v=0wK1127fHQ4&feature=channel_page |title=‪Symptoms of H1N1 (Swine Flu)‬‏ |publisher=YouTube |date=2009-04-28 |accessdate=2011-05-22}}</ref>]]

According to the [[Centers for Disease Control and Prevention]] (CDC), in humans the symptoms of the 2009 "swine flu" H1N1 virus are similar to those of [[influenza]] and of [[influenza-like illness]] in general. Symptoms include [[fever]], [[cough]], [[sore throat]], body aches, [[headache]], [[chills]] and [[fatigue (medical)|fatigue]]. The 2009 outbreak has shown an increased percentage of patients reporting [[diarrhea]] and [[vomiting]].<ref>{{cite web
|url=http://www.cdc.gov/swineflu/swineflu_you.htm
|title=Swine Flu and You
|publisher=[[Centers for Disease Control and Prevention|CDC]]
|date=2009-04-26
|accessdate=2009-04-26
}}</ref> The 2009 H1N1 virus is not zoonotic swine flu, as it is not transmitted from pigs to humans, but from person to person.

Because these symptoms are not specific to swine flu, a [[differential diagnosis]] of ''probable'' swine flu requires not only symptoms, but also a high likelihood of swine flu due to the person's recent history. For example, during the [[2009 swine flu outbreak in the United States]], the CDC advised physicians to "consider swine influenza infection in the differential diagnosis of patients with [[acute febrile respiratory illness]] who have either been in contact with persons with confirmed swine flu, or who were in one of the five U.S. states that have reported swine flu cases or in Mexico during the seven days preceding their illness onset."<ref name=CDCguideHD>{{cite web
|title=CDC Health Update: Swine Influenza A (H1N1) Update: New Interim Recommendations and Guidance for Health Directors about Strategic National Stockpile Materiel
|author=Centers for Disease Control and Prevention
|publisher=Health Alert Network
|date=April 27, 2009
|url=http://www.cdc.gov/swineflu/HAN/042609.htm
|accessdate=April 27, 2009
}}</ref> A diagnosis of ''confirmed'' swine flu requires laboratory testing of a respiratory sample (a simple nose and throat swab).<ref name=CDCguideHD/>

The most common cause of death is [[respiratory failure]]. Other causes of death are [[pneumonia]] (leading to [[sepsis]]),<ref>{{cite web|url=http://www.msnbc.msn.com/id/31889365/ns/health-swine_flu/ |title=Study: Swine flu resembles feared 1918 flu |publisher=MSNBC |date=2009-07-13 |accessdate=2011-05-22}}</ref> high fever (leading to neurological problems), [[dehydration]] (from excessive vomiting and [[diarrhea]]), [[electrolyte imbalance]] and [[Renal failure|kidney failure]].<ref name=kidney>{{cite news
|title=Swine flu can damage kidneys, doctors find
|author=
|publisher=Reuters
|date=April 14, 2010
|url=http://www.reuters.com/article/idUSN14118931
|accessdate=April 17, 2010
}}</ref> Fatalities are more likely in young children and the elderly.

===Diagnosis===
[[File:Singapore Changi Airport Thermal Scanning.JPG|thumb|right|Thermal scanning of passengers arriving at Singapore Changi airport]]
The CDC recommends [[qPCR|real-time]] [[RT-PCR]] as the method of choice for diagnosing H1N1.<ref>{{cite web|url=http://www.cdc.gov/h1n1flu/specimencollection.htm |title=CDC H1N1 Flu &#124; Interim Guidance on Specimen Collection, Processing, and Testing for Patients with Suspected Novel Influenza A (H1N1) (Swine Flu) Virus Infection |publisher=Cdc.gov |date=2009-05-13 |accessdate=2011-05-22}}</ref> This method allows a specific diagnosis of novel influenza (H1N1) as opposed to [[seasonal influenza]]. Near-patient [[Point-of-care testing|point-of-care tests]] are in development.<ref>{{cite web|url=http://www.biosearchtech.com/display.aspx?catid=227&pageid=97 |title=Micronics Acquires License to Biosearch Technologies’ Nucleic Acid Assay Chemistries|publisher=Biosearchtech.com |date=2009-10-28 |accessdate=2011-05-22}}</ref>

==Prevention==
Prevention of swine influenza has three components: prevention in swine, prevention of transmission to humans, and prevention of its spread among humans.

===In swine===
Methods of preventing the spread of influenza among swine include facility management, herd management, and vaccination ([[ATCvet]] code: {{ATCvet|I09|AA03}}). Because much of the illness and death associated with swine flu involves secondary infection by other pathogens, control strategies that rely on vaccination may be insufficient.

Control of swine influenza by vaccination has become more difficult in recent decades, as the [[evolution]] of the [[virus]] has resulted in inconsistent responses to traditional vaccines. Standard commercial swine flu vaccines are effective in controlling the infection when the virus strains match enough to have significant cross-protection, and custom (autogenous) vaccines made from the specific viruses isolated are created and used in the more difficult cases.<ref>
{{cite web
|url=http://nationalhogfarmer.com/mag/swine_flu_virus_endemic/
|publisher=National Hog Farmer
|title=Swine flu virus turns endemic
|date=15 September 2007
}}</ref><ref>{{cite web
|url=http://www.livestock.novartis.com/cv_swine.html
|publisher=Novartis
|work=Custom Vaccines
|title=Swine
}}{{dead link|date=May 2011}}</ref>
Present [[Influenza vaccine|vaccination]] strategies for SIV control and prevention in swine farms typically include the use of one of several bivalent SIV vaccines commercially available in the United States. Of the 97 recent H3N2 isolates examined, only 41 isolates had strong serologic cross-reactions with antiserum to three commercial SIV vaccines. Since the protective ability of influenza vaccines depends primarily on the closeness of the match between the vaccine virus and the epidemic virus, the presence of nonreactive H3N2 SIV variants suggests current commercial vaccines might not effectively protect pigs from infection with a majority of H3N2 viruses.<ref name="pmid17366454"/><ref>{{Cite journal|author=Gramer MR, Lee JH, Choi YK, Goyal SM, Joo HS |title=Serologic and genetic characterization of North American H3N2 swine influenza A viruses |journal=Canadian Journal of Veterinary Research |volume=71 |issue=3 |pages=201–6 |year=2007 |month=July |pmid=17695595 |pmc=1899866}}</ref> The United States Department of Agriculture researchers say while pig vaccination keeps pigs from getting sick, it does not block infection or shedding of the virus.<ref>{{cite web|url=http://www.newscientist.com/article/mg20227063.800-swine-flu-the-predictable-pandemic.html?full=true/|title=Swine flu: The predictable pandemic?|date=2009-04-29}}</ref>

Facility management includes using disinfectants and ambient temperature to control viruses in the environment. They are unlikely to survive outside living cells for more than two weeks, except in cold (but above freezing) conditions, and are readily inactivated by disinfectants.<ref name=Merck/> Herd management includes not adding pigs carrying influenza to herds that have not been exposed to the virus. The virus survives in healthy carrier pigs for up to three months, and can be recovered from them between outbreaks. Carrier pigs are usually responsible for the introduction of SIV into previously uninfected herds and countries, so new animals should be [[quarantine]]d.<ref name=cfsph/> After an outbreak, as immunity in exposed pigs wanes, new outbreaks of the same strain can occur.<ref name=Merck/>

===In humans===
;Prevention of pig-to-human transmission
[[Image:AntigenicShift HiRes vector.svg|thumb|]] Swine can be infected by both avian and human flu strains of influenza, and therefore are hosts where the [[antigenic shift]]s can occur that create new influenza strains.
The transmission from swine to humans is believed to occur mainly in swine farms, where farmers are in close contact with live pigs. Although strains of swine influenza are usually not able to infect humans, this may occasionally happen, so farmers and veterinarians are encouraged to use face [[surgical mask|mask]]s when dealing with infected animals. The use of vaccines on swine to prevent their infection is a major method of limiting swine-to-human transmission. Risk factors that may contribute to swine-to-human transmission include smoking and, especially, not wearing gloves when working with sick animals, thereby increasing the likelihood of subsequent hand-to-eye, hand-to-nose or hand-to-mouth transmission.<ref>{{Cite journal|author=Ramirez A, Capuano AW, Wellman DA, Lesher KA, Setterquist SF, Gray GC |title=Preventing Zoonotic Influenza Virus Infection |journal=Emerging Infect. Dis. |volume=12 |issue=6 |pages=996–1000 |year=2006 |month=June |pmid=16707061 |pmc=1673213 |doi= |url=http://www.cdc.gov/ncidod/eid/vol12no06/05-1576.htm}}</ref>

;Prevention of human-to-human transmission
Influenza spreads between humans when infected people cough or sneeze, then other people breathe in the virus or touch something with the virus on it and then touch their own face.<ref name=CDCspread>
{{cite web
|url=http://www.cdc.gov/swineflu/key_facts.htm
|title=Q & A: Key facts about swine influenza (swine flu) – Spread of Swine Flu
|publisher=Centers for Disease Control and Prevention
|date=24 April 2009
|accessdate=2009-04-26
}}</ref> "Avoid touching your eyes, nose or mouth. Germs spread this way."<ref name="2009 H1N1 Swine Flu and You">{{cite web|url=http://www.cdc.gov/H1N1flu/qa.htm |title=CDC H1N1 Flu &#124; H1N1 Flu and You |publisher=Cdc.gov |date= |accessdate=2011-05-22}}</ref> Swine flu cannot be spread by pork products, since the virus is not transmitted through food.<ref name=CDCspread/> The swine flu in humans is most contagious during the first five days of the illness, although some people, most commonly children, can remain contagious for up to ten days. Diagnosis can be made by sending a specimen, collected during the first five days, for analysis.<ref>
{{cite web
|url=http://www.cdc.gov/swineflu/key_facts.htm
|title=Q & A: Key facts about swine influenza (swine flu) – Diagnosis
|publisher=Centers for Disease Control and Prevention
|date=24 April 2009
|accessdate=2009-04-26
}}</ref>
[[Image:Airport Thermographic Camera.jpg|thumb|Thermal imaging camera and screen, photographed in an airport terminal in Greece - thermal imaging can detect elevated body temperature, one of the signs of the virus H1N1 (swine influenza).]]
Recommendations to prevent spread of the virus among humans include using standard [[Influenza#Infection control|infection control]], which includes frequent washing of hands with soap and water or with [[Hand sanitizer|alcohol-based hand sanitizers]], especially after being out in public.<ref>{{cite web|url=http://cdc.gov/swineflu/investigation.htm|title=CDC - Influenza (Flu) &#124; Swine Influenza (Flu) Investigation|publisher=Cdc.gov|date=|accessdate=2009-04-27}}</ref> Chance of transmission is also reduced by disinfecting household surfaces, which can be done effectively with a diluted chlorine bleach solution.<ref>{{cite web|url=http://www.waterandhealth.org/newsletter/new/winter_2005/chlorine_bleach.html
|title=Chlorine Bleach: Helping to Manage the Flu Risk
|publisher=Water Quality & Health Council
|date=April 2009
|accessdate=2009-05-12
}}</ref>

Experts agree hand-washing can help prevent viral infections, including ordinary and the swine flu infections. Also, avoiding touching one's eyes, nose or mouth with one's hands helps to prevent the flu.<ref name="2009 H1N1 Swine Flu and You" /> Influenza can spread in coughs or sneezes, but an increasing body of evidence shows small droplets containing the virus can linger on tabletops, telephones and other surfaces and be transferred via the fingers to the eyes, nose or mouth. [[Hand sanitizer|Alcohol-based gel or foam hand sanitizers]] work well to destroy viruses and bacteria. Anyone with flu-like symptoms, such as a sudden fever, cough or muscle aches, should stay away from work or public transportation, and should contact a doctor for advice.<ref name="How to protect yourself?">{{cite web| url = http://pn.lifehugger.com/doc/989/Swine_Flu | title = Self protection measures | publisher = LHC | accessdate = 2009-10-15}}</ref>

[[Social distancing]], another tactic, is staying away from other people who might be infected, and can include avoiding large gatherings, spreading out a little at work, or perhaps staying home and lying low if an infection is spreading in a community. [[Public health]] and other responsible authorities have action plans which may request or require social distancing actions, depending on the severity of the outbreak.

====Vaccination====
{{Main|2009 flu pandemic vaccine}}
[[Vaccine]]s are available for different kinds of swine flu. The U.S. [[Food and Drug Administration]] (FDA) approved the new swine flu vaccine for use in the United States on September 15, 2009.<ref name="Vaccine approval news release">{{cite web| url = http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm182399.htm | title = FDA Approves Vaccines for 2009 H1N1 Influenza Virus | publisher = FDA | accessdate = 2009-10-15}}</ref> Studies by the [[National Institutes of Health]] show a single dose creates enough antibodies to protect against the virus within about 10 days.<ref name=autogenerated1>{{cite web| url = http://www.nlm.nih.gov/medlineplus/news/fullstory_89221.html | title = NIH studies on Swine flu vaccine | publisher = NIH | accessdate = 2009-10-15}}{{dead link|date=May 2011}} {{Dead link|date=September 2010|bot=H3llBot}}</ref>

In the aftermath of the 2009 pandemic, several studies were conducted to see who received influenza vaccines. These studies show that whites are much more likely to be vaccinated for seasonal influenza and for the H1N1 strain than African Americans <ref>Uscher-Pines, Lori, Jurgen Maurer, and Katherine M. Harris. "Racial And Ethnic Disparities In Uptake And Location Of Vaccination For 2009-H1N1 And Seasonal Influenza." American Journal Of Public Health 101.7 (2011): 1252-1255. SocINDEX with Full Text. Web. 6 Dec. 2011.</ref> This could be due to several factors. Historically, there has been mistrust of vaccines and of the medical community from African Americans. Many African Americans do not believe vaccines or doctors to be effective. This mistrust stems from the exploitation of the African American communities during studies like the Tuskegee study. Additionally, vaccines are typically administered in clinics, hospitals, or doctor’s offices. Many people of lower socioeconomic status are less likely to receive vaccinations because they do not have health insurance.

==Treatment==
===In swine===
As swine influenza is rarely fatal to pigs, little treatment beyond rest and supportive care is required.<ref name=cfsph>{{cite web|url=http://www.cfsph.iastate.edu/Factsheets/pdfs/influenza.pdf |title=Influenza Factsheet |publisher=Center for Food Security and Public Health, Iowa State University}}</ref> Instead, veterinary efforts are focused on preventing the spread of the virus throughout the farm, or to other farms.<ref name=Kothalawala/> Vaccination and animal management techniques are most important in these efforts. Antibiotics are also used to treat this disease, which although they have no effect against the influenza virus, do help prevent bacterial [[pneumonia]] and other [[secondary infection]]s in influenza-weakened herds.<ref name="cfsph"/>

===In humans===
If a person becomes sick with swine flu, antiviral drugs can make the illness milder and make the patient feel better faster. They may also prevent serious flu complications. For treatment, antiviral drugs work best if started soon after getting sick (within two days of symptoms). Beside antivirals, supportive care at home or in a hospital focuses on controlling fevers, relieving pain and maintaining fluid balance, as well as identifying and treating any secondary infections or other medical problems. The U.S. [[Centers for Disease Control and Prevention]] recommends the use of [[oseltamivir]] (Tamiflu) or [[zanamivir]] (Relenza) for the treatment and/or prevention of infection with swine influenza viruses; however, the majority of people infected with the virus make a full recovery without requiring medical attention or antiviral drugs.<ref>http://www.who.int/csr/disease/swineflu/faq/en/index.html</ref> The virus isolates in the 2009 outbreak have been found resistant to [[amantadine]] and [[rimantadine]].<ref>{{cite web|url=http://www.cdc.gov/swineflu/antiviral_swine.htm |title=Antiviral Drugs and Swine Influenza |publisher=Centers for Disease Control |accessdate=2009-04-27}}</ref>

In the U.S., on April 27, 2009, the FDA issued [[emergency use authorization]]s to make available [[Relenza]] and [[Tamiflu]] [[antiviral drug]]s to treat the swine influenza virus in cases for which they are currently unapproved. The agency issued these EUAs to allow treatment of patients younger than the current approval allows and to allow the widespread distribution of the drugs, including by unlicensed volunteers.<ref>{{cite web|url=http://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm149571.htm |title=''FDA Authorizes Emergency Use of Influenza Medicines, Diagnostic Test in Response to Swine Flu Outbreak in Humans.'' FDA News, April 27, 2009 |publisher=Fda.gov |date=2009-04-27 |accessdate=2009-05-07}}</ref>

==See also==
* [[Infectious disease]]
* [[List of epidemics]]

==Notes==
{{Reflist|30em}}

==Further reading==
{{refbegin|colwidth=30em}}
*{{Cite journal|author=Alexander DJ |title=Ecological aspects of influenza A viruses in animals and their relationship to human influenza: a review |journal=Journal of the Royal Society of Medicine |volume=75 |issue=10 |pages=799–811 |year=1982 |month=October |pmid=6752410 |pmc=1438138}}
*{{Cite journal|author=Hampson AW, Mackenzie JS |title=The influenza viruses |journal=The Medical Journal of Australia |volume=185 |issue=10 Suppl |pages=S39–43 |year=2006 |month=November |pmid=17115950 |url=http://www.mja.com.au/public/issues/185_10_201106/ham10884_fm.html}}
*{{Cite journal|author=Lipatov AS |title=Influenza: Emergence and Control |journal=Journal of Virology |volume=78 |issue=17 |pages=8951–9 |year=2004 |month=September |pmid=15308692 |pmc=506949 |doi=10.1128/JVI.78.17.8951-8959.2004|author-separator=,|author2=Govorkova EA|author3=Webby RJ|display-authors=3|last4=Ozaki|first4=H.|last5=Peiris|first5=M.|last6=Guan|first6=Y.|last7=Poon|first7=L.|last8=Webster|first8=R. G.}}
*{{Cite journal|author=Van Reeth K |title=Avian and swine influenza viruses: our current understanding of the zoonotic risk |journal=Veterinary Research |volume=38 |issue=2 |pages=243–60 |year=2007 |pmid=17257572 |doi=10.1051/vetres:2006062}}
*{{Cite journal|author=Webster RG, Bean WJ, Gorman OT, Chambers TM, Kawaoka Y |title=Evolution and ecology of influenza A viruses |journal=Microbiological Reviews |volume=56 |issue=1 |pages=152–79 |year=1992 |month=March |pmid=1579108 |pmc=372859 |url=http://mmbr.asm.org/cgi/pmidlookup?view=long&pmid=1579108}}
*{{Cite journal|author=Winkler WG |title=Influenza in animals: its possible public health significance |journal=Journal of Wildlife Diseases |volume=6 |issue=4 |pages=239–42; discussion 247–8 |year=1970 |month=October |pmid=16512120 |url=http://www.jwildlifedis.org/cgi/pmidlookup?view=long&pmid=16512120}}
{{refend}}

==External links==
{{Commons category|Swine flu}}
{{Wikinews|Category:Swine flu|Swine flu}}
* Swine influenza: [http://pn.lifehugger.com/doc/989/Swine_Flu Slideshow]
* [http://www.direct.gov.uk/pandemicflu UK National Pandemic Flu Service]
* [http://www.direct.gov.uk/en/Swineflu/DG_177831 Official UK government information on swine flu from Directgov]
* [http://www.nhs.uk/ Official swine flu advice and latest information from the UK National Health Service]
* [http://fora.tv/2009/04/30/Understanding_Swine_Flu_Influenza_A_H1N1 8 minute video answering common questions about the subject] on [[fora.tv]]
* [http://www.theairdb.com/swine-flu/heatmap.html Swine flu charts and maps] Numeric analysis and approximation of current active cases
* [http://www.cnn.com/2009/HEALTH/04/28/regular.flu/index.html Worried about swine flu? Then you should be terrified about the regular flu.]
* [http://www.cdc.gov/swineflu/ Centers for Disease Control and Prevention (CDC) - Swine Flu]
* [http://www.cidrap.umn.edu/cidrap/content/influenza/swineflu/resources/swineflures.html Center for Infectious Disease Research and Policy - Novel H1N1 influenza resource list]
* [http://www.pandemicflu.gov/ Pandemic Flu US Government Site]
* [http://www.who.int/en/ World Health Organization (WHO): Swine influenza]
* [http://www.nlm.nih.gov/medlineplus/swineflu.html Medical Encyclopedia Medline Plus: Swine Flu]
* [http://www.swine-flu-news.us/ Swine Flu News and Updates From Around the World]
* [http://www.swineflutracker.co.uk/ Swine Flu Tracker]
* [http://ec.europa.eu/health-eu/health_problems/avian_influenza/index_en.htm Health-EU portal] EU response to influenza
* [http://ec.europa.eu/health/ph_threats/com/Influenza/h1n1_en.htm European Commission - Public Health] EU coordination on Pandemic (H1N1) 2009
{{influenza}}

{{DEFAULTSORT:Swine Influenza}}
[[Category:Animal virology]]
[[Category:Health disasters]]
[[Category:Influenza]]
[[Category:Pandemics]]
[[Category:Swine diseases]]

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[[zh-min-nan:Ti-liû-kám]]
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[[be-x-old:Сьвіны грып]]
[[bs:Svinjska gripa]]
[[ca:Grip porcina]]
[[cs:Chřipka prasat]]
[[cy:Ffliw moch]]
[[da:Svineinfluenza]]
[[pdc:Seifiewer]]
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[[dv:އޫރު ރޯގާ]]
[[et:Seagripp]]
[[el:Γρίπη H1N1]]
[[es:Gripe porcina]]
[[eo:Porka gripo]]
[[fa:آنفلوآنزای خوکی]]
[[fr:Grippe porcine]]
[[ga:Fliú na muc (galar)]]
[[gl:Gripe porcina]]
[[gan:豬流感]]
[[ko:돼지 인플루엔자]]
[[hi:शूकर इन्फ्लूएंजा]]
[[id:Flu babi]]
[[ia:Influenza porcin]]
[[is:Svínaflensa]]
[[it:Influenza suina]]
[[he:שפעת החזירים]]
[[jv:Flu babi]]
[[kn:ಹಂದಿಜ್ವರ]]
[[ka:ღორის გრიპი]]
[[ht:Grip pòsin]]
[[lo:ໄຂ້ຫວັດຫມູ]]
[[la:Influentia porcina]]
[[lv:Cūku gripa]]
[[lt:Kiaulių gripas]]
[[hu:Sertésinfluenza]]
[[mk:Свински грип]]
[[ml:പന്നിപ്പനി]]
[[mt:Influwenza tal-majjali]]
[[mr:स्वाइन इन्फ्लूएन्झा]]
[[arz:انفلوانزا الخنازير]]
[[ms:Influenza babi]]
[[mn:Гахайн томуу]]
[[nah:Ātōnahuiztli Influenza A H1N1]]
[[nl:Varkensgriep]]
[[ja:豚インフルエンザ]]
[[no:Svineinfluensa]]
[[nn:Influensa A(H1N1)]]
[[pap:Griep di porco]]
[[ps:سرکوزي والګی]]
[[pl:Świńska grypa]]
[[pt:Gripe suína]]
[[ru:Свиной грипп]]
[[sq:Gripi i derrit]]
[[si:සූකර උණ]]
[[simple:Swine influenza]]
[[sk:Chrípka ošípaných]]
[[sl:Nova gripa]]
[[so:Hargab Doofaar]]
[[sr:Свињски грип]]
[[fi:Sikainfluenssa]]
[[sv:Svininfluensa]]
[[tl:Trangkasong baboy]]
[[ta:எச்1.என்1 சளிக்காய்ச்சல்]]
[[th:ไข้หวัดใหญ่ในสุกร]]
[[tr:Domuz gribi]]
[[uk:Свинячий грип]]
[[ur:Swine influenza]]
[[vi:Cúm lợn]]
[[wuu:猪流感]]
[[yi:חזיר גריפע]]
[[zh-yue:豬流感]]
[[bat-smg:Kiauliu grips]]
[[zh:豬流感]]

Revision as of 12:28, 23 January 2012

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