Bird flu (avian influenza) is a disease caused by an influenza virus that primarily affects birds. In the late 1990s, a new strain of bird flu arose that was remarkable for its ability to cause severe disease and death, especially in domesticated birds such as ducks, chickens, or turkeys. As a result, this strain was called highly pathogenic (meaning very severe) avian influenza.
Since the identification of highly pathogenic influenza, infected birds have been found in Asia, Europe, the Middle East, and Africa. Careful control measures, including destroying infected flocks and vaccinating healthy birds, have reduced the number of cases, but the virus continues to exist in poultry flocks in areas of Asia and Africa. Bird flu from the highly pathogenic strain is not found in the United States at this time.
The virus spreads from bird to bird through infected birds shedding the virus in their saliva, nasal secretions, and droppings. Healthy birds get infected when they come into contact with contaminated secretions or feces from infected birds. Contact with contaminated surfaces such as cages might also allow the virus to transfer from bird to bird. Symptoms in birds range from mild drops in egg production to failure of multiple major organs and death.
The first human case of illness from highly pathogenic avian influenza was identified in 1997, and more than 560 cases have been identified since then, with deaths worldwide exceeding 300. Human cases of highly pathogenic bird flu have been largely confined to Southeast Asia and Africa. However, mutations often occur in the virus, and it is possible that some mutations could create a more contagious virus that could cause a regional epidemic or a worldwide pandemic of bird flu among humans. Fortunately, the mutations that have occurred to date have not made the virus more contagious, although the concern remains.