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CDC - Avian Influenza in Birds Information

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  • CDC - Avian Influenza in Birds Information

    Avian influenza refers to infection with avian influenza Type A viruses. These viruses occur naturally among wild aquatic birds worldwide and can infect domestic poultry and other bird and animal species. Wild aquatic birds can be infected with avian influenza A viruses in their intestines and respiratory tract, but usually do not get sick. However, avian influenza A viruses are very contagious among birds and some of these viruses can sicken and even kill certain domesticated bird species including chickens, ducks, and turkeys.

    Infected birds can shed avian influenza A viruses in their saliva, nasal secretions, and feces. Susceptible birds become infected when they have contact with virus contaminated secretions or excretions or with surfaces that are contaminated with virus secretions or excretions from infected birds.

    Avian influenza A viruses are classified into the following two categories: low pathogenic avian influenza A (LPAI) viruses, and highly pathogenic avian influenza A (HPAI) viruses. The categories refer to the ability to cause severe disease, based upon molecular characteristics of the virus and mortality in birds under experimental conditions.

    Avian Influenza in Wild Birds

    Avian influenza A viruses have been isolated from more than 100 different species of wild birds. The majority of the wild birds from which these viruses have been recovered represent gulls, terns and shorebirds or waterfowl such as ducks, geese and swans. These wild birds are often viewed as reservoirs (hosts) for avian influenza A viruses.


    Avian Influenza in Poultry (Domesticated Birds)

    Domesticated birds (chickens, turkeys, etc.) and semi-domesticated birds (crows) may become infected with avian influenza A viruses through direct contact with infected waterfowl or other infected poultry, or through contact with surfaces (such as dirt or cages) or materials (such as water or feed) that have been contaminated with the viruses.

    Infection of poultry with LPAI viruses may cause no disease or mild illness and may only cause mild signs (such as ruffled feathers and a drop in egg production) and may not be detected. Infection of poultry with HPAI viruses can cause severe disease with high mortality. Both HPAI and LPAI viruses can spread rapidly through flocks of poultry. HPAI virus infection can cause disease that affects multiple internal organs with mortality up to 90-100%, often within 48 hours.


    Avian Influenza A Virus Infections in U.S. Poultry (Domesticated Birds)

    Worldwide, avian influenza outbreaks occur among poultry from time to time. Since 1997, for example, based on the World Organization for Animal Health (OIE) reporting criteria for Notifiable Avian Influenza in commercial poultry, the United States has experienced 19 incidents of H5 and H7 low pathogenic avian influenza in commercial poultry, and one incident of highly pathogenic avian influenza in commercial poultry that was restricted to one poultry farm. The U.S. Department of Agriculture monitored and responded to these incidents.

    In 2004, the United States experienced the first highly pathogenic avian influenza outbreak among poultry in 20 years. This was an outbreak caused by highly pathogenic avian influenza A (H5N2) virus which occurred in Texas. The outbreak was reported in a flock of 7,000 chickens in south-central Texas. No transmission of highly pathogenic avian influenza A(H5N2) virus to humans was reported.

    For more information on reportable poultry outbreaks of avian influenza, visit the World Organization for Animal Health (OIE).

    Page last reviewed: November 25, 2011
    Page last updated: November 25, 2011
    Content source: Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD)
    Last edited by sharon sanders; December 6, 2011, 12:32 PM. Reason: added