Swine influenza virus (referred to as SIV) refers to influenza cases that are caused by Orthomyxoviruses that are endemic to pig populations. SIV strains isolated to date have been classified either as Influenzavirus C or one of the various subtypes of the genus Influenzavirus A.
Swine flu, unlike bird flu, is able to pass from human to human contact.
Swine influenza is known to be caused by influenza A subtypes H1N1, H1N2, H3N1, H3N2 and H2N3.
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 (HA, NA, and PB1), swine (NS, NP, and M), and avian (PB2 and PA) lineages.
Signs and symptoms
Main symptoms of swine flu in humans.
The Centers for Disease Control and Prevention (CDC) have stated that the symptoms of swine flu are similar to those of other strains of human flu, including fever, cough, sore throat, body aches, headache, chills and fatigue. A few patients have reported that they also suffered from diarrhea and vomiting.
Causes
H5N1
Avian influenza virus H3N2 is endemic in pigs in China and has been detected in pigs in Vietnam, increasing fears of the emergence of new variant strains. 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 genes and mutating into a form which can pass easily among humans. H3N2 evolved from H2N2 by antigenic shift. In August 2004, researchers in China found H5N1 in pigs. Measured resistance to the standard antiviral drugs amantadine and rimantadine in H3N2 in humans has increased to 92% in 2005.
Chairul Nidom, a virologist at Airlangga University's tropical disease center in Surabaya, East Java, conducted an independent research; he tested the blood of 10 apparently healthy pigs housed near poultry farms in West Java where avian flu had broken out, Nature reported. 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.
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