Avian (Flu) Influenza


Birds have their own influenza (flu) viruses, known as bird flu or avian influenza (AI) that is caused by type A influenza viruses. These viruses may or may not cause outbreaks in birds. Occasionally, these viruses can also infect humans, and sometimes cause an outbreak or, very rarely, a pandemic. There are many avian influenza viruses that affect birds.

  • Avian influenza viruses are very common throughout the world.
  • Outbreaks of many different kinds of avian influenza occur commonly among poultry in the United States.
  • Avian influenza viruses occur naturally among birds. Wild birds worldwide carry the viruses, but usually do not get sick from them. However, some avian influenza strains are very contagious among birds, and can be deadly to different types of birds, including chickens, ducks, and turkeys.
  • There are two general classifications for avian influenza viruses: low pathogenic (LPAI) that generally causes little or no clinical signs in birds and highly pathogenic (HPAI) that can cause severe clinical signs and death in birds.

Avian influenza viruses usually do not affect people, but once in a while may infect people cause mild to severe illness in humans.

  • Human cases are mostly found in people who have close contact with infected birds.
  • Public health officials worldwide are closely watching for any signs that would indicate if or when avian influenza viruses have changed into a form that could be spread from person-to-person.
  • The recent outbreak in China has been caused by a novel avian influenza A (H7N9) and is not the same H7N9 virus found in North American birds.
  • Another avian influenza virus of interest is known as avian influenza (HPAI) A (H5N1).
  • To date, there have been 10 outbreaks of various avian influenza viruses among poultry in the United States with no known transmission to humans. There have only been two outbreaks in the United States involving transmission to humans.