Information on Swine Influenza/Variant Influenza Viruses
Swine influenza (swine flu) 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
- trH1N2 virus
Swine flu viruses do not normally infect humans. However, sporadic human infections with swine influenza viruses have occurred. When this happens, these viruses are called “variant viruses.” They also can be denoted by adding the letter “v” to the end of the virus subtype designation. Human infections with H1N1v, H3N2v and H1N2v viruses have been detected in the United States.
The links below offer key information for different audiences about swine influenza in pigs and variant influenza virus infections in humans.
Variant Influenza Viruses in Humans
- Human Infections with Variant Influenza Viruses (Viruses That Normally Circulate in Pigs)
- Key Facts about Human Infections with Variant Viruses
- Reported Infections with Variant Influenza Viruses in the United States since 2005
- Influenza A (H3N2) Variant Virus
- Interim Guidance for Clinicians on Human Infections with Variant Influenza Viruses
- Guidance Documents Related to Preventing the Spread of Influenza A Viruses
- Reports of Human Infections with Variant Viruses
Information and materials, including educational posters [389 KB, 1 page] that can be displayed around animal exhibits, are available in Compendium of Measures to Prevent Disease Associated with Animals in Public Settings, 2013.
Dr. Lyn Finelli discusses CDC’s recommendations for reducing the risk of infection with H3N2v flu viruses for fairgoers and swine exhibitors.
- Page last reviewed: August 12, 2016
- Page last updated: August 15, 2016
- Content source:
- Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)
- Page maintained by: Office of the Associate Director for Communication, Digital Media Branch, Division of Public Affairs