Swine influenza virus (referred to as Swine influenza viruses or SIV) refers to influenza cases that are caused by Orthomyxoviruses endemic to populations of pigs. SIV strains isolated to date have been classified either as Influenzavirus C or one of the various subtypes of the genus Influenzavirus A.[1]
Swine flu infects people every year and is found typically in people who have been in contact with pigs, although there have been cases of person-to-person transmission.[2] Symptoms include: fever, disorientation, stiffness of the joints, vomiting, and loss of conciousness ending in death.[3] Influenza A virus subtypes H1N1, H1N2, H3N1 and H3N2 are all known to cause SIV infections.[4][5] and H2N3.[6]
In swine, three influenza A virus subtypes (H1N1, H3N2, and H1N2) are circulating throughout the world.[citation needed] 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. Most H3N2 virus isolates are triple reassortants, meaning that it contains genes from human (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages.[citation needed]
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