What Is Swine Flu - 25 Countries Effected From Swine Flu - Swine influenza also called pig influenza, is an infection by any one of several types of swine influenza virus. Swine influenza virus is common throughout pig populations worldwide. Swine Flu stated from the Mexico. Transmission of the virus from pigs to humans is not common and does not always lead to human influenza, often resulting only in the production of antibodies in the blood.