Swine flu is a form of influenza which is very common in pigs. It is a respiratory disease which is highly contagious and it is caused by orthomyxo virus. Swine flu can affect human beings sporadically specially those who are in direct exposure to pigs. But it can spread through air and cause an epidemic. Most common virus of this flu is influenza virus A with sub-types of H1N1 which has recently hit America.