Swine Influenza (Influenza in Swine)
Swine Influenza (swine flu) is a respiratory disease of pigs caused by type A influenza virus that regularly causes outbreaks of influenza in pigs. Swine flu viruses can cause high levels of illness in pig herds, but cause few deaths in pigs. Swine influenza viruses can circulate among swine throughout the year, but most outbreaks occur during the late fall and winter months similar to outbreaks of seasonal influenza in humans. The main swine flu viruses circulating in U.S. pigs in recent years are: swine triple reassortant (tr) H1N1, trH3N2 and trH1N2. With the exception of the 2009 H1N1 virus, influenza viruses that circulate in swine are very different from influenza viruses that commonly circulate in people.
Information about swine influenza in humans (called variant viruses) is available at Variant Influenza Viruses in Humans.