Avian influenza (AI) is caused by an influenza type A virus which can infect poultry (such as chickens, turkeys, pheasants, quail, domestic ducks, geese, and guinea fowl) and wild birds (especially waterfowl).
AI viruses are classified by a combination of two groups of proteins: hemagglutinin or “H” proteins, of which there are 16 (H1–H16), and neuraminidase or “N” proteins, of which there are 9 (N1–N9). AI viruses are further classified by their pathogenicity—the ability of a particular virus strain to produce disease in domestic chickens.
Highly pathogenic avian influenza (HPAI) virus strains are extremely infectious, often fatal to chickens, and can spread rapidly from flock-to-flock.
Low pathogenicity avian influenza (LPAI) virus strains occur naturally in wild migratory waterfowl and shorebirds without causing illness. LPAI can infect domestic poultry, creating little or no signs of illness.
The U.S. Department of Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS) works closely with States and the poultry industry to prevent AI from becoming established in the U.S. poultry population. Keeping our nation’s poultry free from avian influenza helps protect our farmers’ livelihoods.