Swine influenza virus ( often shortened to SIV or swine flu ) is one of a number of viruses that are endemic to pigs . 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 . Swine influenza virus ( SIV ) or S-OIV ( swine-origin influenza virus ) is any strain of the influenza family of viruses that is endemic in pigs .