Swine influenza (also called swine flu, hog flu and pig flu) refers to influenza caused by those strains of influenza virus, called swine influenza virus (SIV), that usually infect (is endemic in) pigs. As of 2009 these strains are all found in Influenza C virus and the subtypes of Influenza A virus known as H1N1, H1N2, H3N1, H3N2, and H2N3. Swine influenza is common in pigs in the midwestern United States (and occasionally in other states), Mexico, Canada, South America, Europe (including the United Kingdom, Sweden, and Italy), Kenya, Mainland China, Taiwan, Japan and other parts of eastern Asia.