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Bird Flu (Avian Influenza, Avian Flu)

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Medical Author:

Mary D. Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.

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Medical Editor:

Charles Patrick Davis, MD, PhD

Charles Patrick Davis, MD, PhD

Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.

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Bird flu facts

• Bird flu refers to strains of influenza that primarily affect wild and domesticated birds.
• Bird flu is also known as avian flu or avian influenza.
• Although bird flu is contagious and spreads easily among birds, it is uncommon for it to be transmitted to humans.
• In the late 1990s, a new strain of bird flu arose which was unusually severe ("highly pathogenic"), resulting in the deaths of hundreds of millions of birds, including poultry.
• Control efforts, including culling infected flocks and vaccinating healthy birds, have limited the spread of highly pathogenic bird flu.
• In 2011, a mutated strain of highly pathogenic bird flu appeared, which is concerning because the existing poultry vaccines are not very effective against the new strain.
• Human infection with the highly pathogenic strain of bird flu is uncommon, with fewer than 600 cases reported since 1997.
• Human infection occurs primarily in people who have close contact with sick poultry in countries where the virus is found. There have been isolated cases of human-to-human transmission.
• Human infection with bird flu is fatal in approximately 60% of cases.
• Bird flu from the highly pathogenic strain is not found in the United States at this time.

What is bird flu?

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.