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Information on Swine Influenza/Variant Influenza Virus

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. The main swine influenza viruses circulating in U.S. pigs in recent years have been, swine triple reassortant (tr) H1N1 influenza virus, trH3N2 virus, and trH1N2 virus.