Avian Influenza

Avian influenza (AI) is a disease caused by a virus that infects domestic poultry and wild birds (primarily geese, ducks and shorebirds). Each year, there is a bird flu season just as there is for humans and, as with people, some forms of the flu are worse than others.

AI strains are divided into two groups based on the pathogenicity of the virus—the ability of the virus to produce disease.

Low Pathogenicity Avian Influenza (LPAI): Most AI strains are classified as low pathogenicity and cause few clinical signs in infected birds. LPAI generally does not pose a significant health threat to humans. However, LPAI is monitored because two strains of LPAI—the H5 and H7 strains–can mutate into highly pathogenic forms.

High Pathogenicity Avian Influenza (HPAI): This type of avian influenza is frequently fatal to birds and easily transmissible between susceptible species. The strain that is currently of concern in Asia, Europe, the Middle East and Africa is the H5N1 HPAI virus.

Currently, the highly pathogenic strain of H5N1 avian influenza is not present in the United States . It is possible that the highly pathogenic strain of H5N1 avian influenza will spread to this country, and the U.S. Government is taking steps to prepare for and minimize the potential impact of the occurrence of this disease in the United States .

Most avian influenza viruses have been isolated from wild waterfowl (ducks, geese, and swans) shorebirds (wading birds), gulls, and terns. With rare exception, the thousands of flu isolates found in wild birds have been low pathogenic avian influenza and have rarely caused signs of illness.

There are a number of ways that highly pathogenic H5N1 could potentially reach the United States—wild bird migration, illegal smuggling of birds or poultry, travel by infected people or people traveling with virus-contaminated articles from regions where H5N1 already exists.