What is swine flu?

Swine flu (swine influenza) is a disease of pigs. It is a highly contagious respiratory disease caused by one of many Influenza A viruses. Approximately 1% to 4% of pigs that get swine flu die from it. It is spread among pigs by direct and indirect contact, aerosols, and from pigs that are infected but do not have symptoms. In many parts of the world pigs are vaccinated against swine flu.

Most commonly, swine flu is of the H1N1 influenza subtype. However, they can sometimes come from the other types, such as H1N2, H3N1, and H3N2.

The current outbreak of swine flu that has infected humans is of the H1N1 type - this type is not as dangerous as some others.

Avian Influenza (Bird Flu) can also infect pigs

Avian flu and human seasonal flu viruses can infect pigs, as well as swine influenza. The H3N2 influenza virus subtype, a virulent one, is thought to have come from pigs - it went on to infect humans.

It is possible for pigs to be infected with more than one flu virus subtype simultaneously. When this happens the genes of the viruses have the opportunity to mingle. When different flu subtypes mix they can create a new virus which contains the genes from several sources - a reassortant virus.