USGS Frequently Asked Questions

Answer:

• The designation of low or highly pathogenic avian influenza refers to the potential for these viruses to kill domestic poultry. The designation of “low pathogenic” or “highly pathogenic” does not refer to how infectious the viruses may be to humans.
• Most strains of avian influenza are not highly pathogenic and cause few signs in infected wild birds; however, in poultry, low pathogenic strains can mutate into a highly pathogenic avian influenza (HPAI) strain that causes extremely contagious, severe illness, and often death, in poultry.
• Influenza viruses are also differentiated by two proteins, hemagglutinin (H) and neuraminidase (N), which are found on the surface of the virus. There are 144 theoretical combinations of the 16 different H and 9 different N proteins that make up the subtypes of avian influenza.
• These subtypes can be further genetically differentiated into strains. A subtype such as the highly pathogenic H5N1 avian influenza virus may have multiple strains. These different strains may be more or less pathogenic to domestic poultry, wild birds, and humans.
• Highly pathogenic avian influenza viruses in poultry are usually H5 or H7 subtypes of Type A influenza, although low pathogenic forms of these H5 and H7 viruses also exist.
• If a strain of the HPAI mutates to become easily transmissible from human-to-human, the new strain would then be considered a human Type A influenza virus.