Swine flu (swine influenza) is a respiratory disease. It caused by viruses (influenza viruses) that infect the respiratory tract of pigs and result in nasal secretions, a barking-like cough, decreased appetite, and listless behavior. Swine flu produces most of the same symptoms in pigs as human flu produces in people. Swine flu can last about one to two weeks in pigs that survive.
Humans do not normally become infected with swine flu. However, there have been periodic human infections; most of these cases occur in people with direct exposure to pigs (e.g., people working on pig farms).
H1N1 flu virus (human swine flu) is contagious. Person–to–person transmission of H1N1 flu virus (human swine flu) has been documented, but it is not clear how easily the virus is spread among people. It is believed that it is spread the same way as regular seasonal influenza. A person infected with H1N1 flu virus can infect others starting 1 day before symptoms develop and up to 7 or more days after becoming ill.