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Section 1. Avian Influenza Facts

Virus Characteristics


Subtypes:
There are many different avian influenza (AI) viruses and they are characterized into subtypes based on two proteins found on the virus called hemagglutinin (H) and neuraminidase (N). 1,6
  • Hemagglutinin (H) proteins are responsible for binding the virus to the cell that is being infected. There are 16 H subtypes. (H1 to H16)
  • Neuraminidase (N) proteins help the virus get into a host cell. There are 9 N subtypes. (N1 to N9)
Birds can carry 144 possible combinations of influenza A subtypes. One very commonly occurring subtype is H5N1.
AI structure CDC
Adapted from CDC Image Library: Dan Higgins

Categories:

AI is also classified into two categories, Low Pathogenic Avian Influenza (LPAI) and Highly Pathogenic Avian Influenza (HPAI) based on the severity of the disease they cause.

  • LPAI is the most common form of AI. Signs of disease range from none, to ruffled feathers and a decrease in egg production. Subtypes LPAI H5 and H7 are carefully monitored as they have been known to mutate into HPAI.
  • HPAI is less common, but spreads rapidly in poultry flocks, causing severe illness, and can kill 90 - 100% of infected birds within 48 hours of exposure.