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Avian Influenza is a disease of wild birds and domestic poultry caused by many different subtypes of Type A influenza virus. The natural reservoir for Type A influenza viruses is wild water birds such as ducks and geese. New influenza A subtypes are continually emerging in the waterfowl population due to the constant mutation of the virus. While avian influenza is caused by Type A viruses, seasonal influenza outbreaks in people are caused by either Type A or Type B influenza viruses. Type A viruses are found in both people and animals, whereas Type B viruses are normally only found in humans.

Influenza Subtypes

Influenza subtypes are named for two antigens present on the surface of the virus:

• H (hemagglutinin)

• N (neuraminidase)
  

There are 16 possible H antigens and 9 possible N antigens. Virus subtypes are named by their combination (e.g., H9N2, H5N1). Avian influenza viruses are classified by the severity of the disease they cause in domestic poultry as either:

• Low Pathogenicity Avian Influenza (LPAI)

• High Pathogenicity Avian Influenza (HPAI)
  

While it is common practice to equate "avian influenza" directly with HPAI H5N1, this is not accurate. There are many different H and N antigenic combinations that can cause avian influenza, and the H and N antigens do not, in and of themselves, determine pathogenicity. Both HPAI H5N1 and LPAI H5N1 avian influenza viruses exist.

Biosecurity Resources

• USDA Defend the Flock Program: Resources

• Testing for Highly Pathogenic Avian Influenza Virus — Washington Animal Disease Diagnostic Laboratory

• Secure Poultry Supply (University of Minnesota)

• Poultry Biosecurity — A guide to writing a biosecurity plan

• Poultry Houses: Biosecurity — Penn State Extension

• Avian Influenza Biosecurity for Backyard Flock Owners — Online Course

• Avian Influenza Biosecurity for Youth and 4-H Members — Online Course