Swine influenza
![H1N1 flu virus particles, SEM. © Science Photo Library](https://www.ecdc.europa.eu/sites/default/files/styles/is_large/public/images/Influenza-in-swine_H.jpg?itok=v3X6fahO)
Swine influenza is a respiratory disease of pigs caused by type A influenza viruses that regularly cause outbreaks of influenza in pigs. Influenza viruses that commonly circulate in swine are called “swine influenza viruses” or “swine flu viruses.” Like human influenza viruses, there are different subtypes and strains of swine influenza viruses.