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News Release

Release No. 0511.05
USDA Press Office (202) 720-4623

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March 2006

Avian influenza (AI) is a virus that causes disease in various types of birds, thus the common name "bird flu." AI viruses can infect chickens, turkeys, pheasants, quail, ducks, geese and guinea fowl as well as a wide variety of other birds, including migratory waterfowl. Each year, there is a flu season for birds just as there is for humans and, as with people, some forms of the flu are worse than others.

To understand the differences and potential threat to U.S. bird populations, this fact sheet provides definitions, a historical perspective, and an outline of USDA prevention and response efforts.



AI viruses are classified by a combination of two groups of proteins found on the surface of the virus: hemagglutinin proteins (H), of which there are 16 (H1-H16), and neuraminidase proteins (N), of which there are 9 (N1-N9). AI strains also 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 is a more pathogenic type of avian influenza that is frequently fatal to birds and easily transmissible between susceptible species. The strain that is currently of concern in Southeast Asia, the Middle East, Africa and Europe is the H5N1 HPAI virus.


AI is primarily spread by direct contact between healthy and infected birds through respiratory secretions and feces. The disease also can be spread through indirect contact if healthy birds are exposed to contaminated equipment or materials.

The HPAI H5N1 virus can be spread from birds to people as a result of extensive direct contact with infected birds. Broad concerns about public health relate to the potential for the virus to mutate, or change into a form that could spread from person to person. The U.S. Department of Health and Human Services is aggressively working to ensure public health is protected. More information about the joint efforts of the federal government is available at http://www.pandemicflu.gov/.


Incidents of LPAI are commonly detected in domestic poultry flocks. Typically, LPAI does not pose a serious threat to human health.

There is no evidence that HPAI currently exists in the United States based on extensive and regular testing of U.S. poultry flocks. Historically, there have been three HPAI outbreaks in poultry in this country--in 1924, 1983 and 2004. No significant human illness resulted from these outbreaks.

The 1924 H7 HPAI outbreak was detected in and eradicated in East Coast live bird markets.

The 1983-84 H5N2 HPAI bird outbreak resulted in the destruction of approximately 17 million chickens, turkeys, and guinea fowl in the northeastern United States to contain and eradicate the disease.

In 2004, USDA confirmed an H5N2 HPAI outbreak in chickens in the southern United States. The disease was quickly eradicated thanks to close coordination and cooperation between USDA, state, local, and industry leaders. Because of the quick response, the disease was limited to one flock.



Import restrictions: As a primary safeguard, USDA maintains trade restrictions on the importation of poultry and poultry products from countries where the H5N1 HPAI strain has been detected in commercial or traditionally raised poultry, not in wild or migratory birds. Additionally, USDA has increased its monitoring of domestic commercial markets for illegally smuggled poultry and poultry products.

Quarantine: All imported live birds must be quarantined for 30 days at a USDA quarantine facility and tested for the avian influenza virus before entering the country. Home quarantine and testing for AI also is required for returning U.S.-origin pet birds.

International Assistance: USDA is working closely with international organizations like the World Organization for Animal Health, the United Nations' Food and Agriculture Organization, and World Health Organization to assist HPAI-affected countries and other neighboring Asian-Pacific countries, as well as Europe, with disease prevention, management, and eradication activities. This includes providing training to scientists in those countries. By helping these countries prepare for, manage, and eradicate HPAI outbreaks, USDA can reduce the risk of the disease spreading to the United States.


USDA works with federal, state, and industry partners to monitor U.S. bird populations. Surveillance is conducted in four key areas: live bird markets, commercial flocks, backyard flocks, and migratory bird populations.

To address the persistence of LPAI associated with the live bird marketing system in the United States, USDA continues to institute a cooperative programs with states and industry to prevent and control the disease not only in the markets themselves, but also among production premises and poultry distributors that supply those markets. The program establishes an important relationship that requires commercial and noncommercial industries to work together to protect America's flocks.

Live Bird Markets: A federal control and prevention program targeting the live bird marketing system involves regular monitoring and surveillance of all facilities in the voluntarily participating states, which are California, Delaware, Florida, Georgia, Illinois, Indiana, Kentucky, Maine, Maryland, Massachusetts, Minnesota, Missouri, New Jersey, New York, North Carolina, Ohio, Pennsylvania, South Carolina, Texas, Virginia and Vermont. Those states with live bird markets that do not participate in the federal program have a state poultry surveillance program in place.

Commercial Flocks: The program in commercial poultry is administered through the National Poultry Improvement Plan (NPIP) and includes monitoring of poultry production facilities and random testing of poultry flocks with tests performed on all birds that appear ill. As part of the program, USDA has worked with states to develop state response and containment plans.

Backyard Flocks: Through the "Biosecurity for the Birds" program, USDA continues to encourage backyard and small poultry producers to strengthen biosecurity practices in order to prevent the introduction of AI into their flocks. This program provides important information about reducing the chances of these birds becoming infected with AI. Biosecurity refers to the application of practical management practices that help to prevent AI and other poultry diseases.

Migratory Birds: Since 1998, USDA scientists, in cooperation with the U.S. Department of the Interior (DOI), have monitored wild migratory birds for AI viruses, having tested more than 12,000 birds in the Alaska flyway, and since 2000, tested more than 4,000 birds in the Atlantic flyway. USDA and DOI are expanding AI surveillance of major migratory flyways in the United States. Included in those projects are agreements with several universities to increase surveillance in the continental U.S. and in other countries.


Funding/Personnel: USDA provides funding and support personnel to states when LPAI is detected. Close attention is paid to H5 and H7 LPAI strains, because of their potential to mutate into HPAI. When HPAI is detected, APHIS personnel are primary responders to control the virus because of the disease infectivity and high mortality rate among poultry.

Bird Vaccine: USDA maintains a bank of avian influenza vaccine, which contains 40 million doses, for birds that would be available if needed, in the event of a HPAI outbreak in the United States. USDA currently is expanding this existing avian influenza vaccine bank to add another 30 million additional doses.

Response Plans: USDA works closely with its federal, state, and tribal partners, as well as industry stakeholders to ensure that effective and coordinated emergency response plans are ready should an outbreak of HPAI occur in the United States.

LPAI response: If LPAI is detected, USDA works with the affected state, which is the lead. A series of measures are undertaken to clean, disinfect, and depopulate the affected premises in order to quickly contain and eradicate the disease.

HPAI response: If HPAI is detected, USDA is the lead and will work with the affected State Department of Agriculture and the affected premises to quarantine, clean, disinfect, and cull the infected and exposed bird population in order to quickly contain and eradicate the disease. As part of the response, USDA will notify the U.S. Department of Health and Human Services' Centers for Disease Control. Additionally, USDA works with the affected premises to compensate owners for the loss of culled birds due to the disease outbreak. These birds can be infected, are considered to be exposed because they are on the same premises as infected birds and birds that are in an eradication zone for the disease.


Testing: USDA scientists developed a rapid diagnostic test for avian influenza and continue to improve the test's sensitivity. The rapid test diagnoses avian influenza within three hours, compared with up to two weeks required for previous tests.

Genetics: USDA scientists also are studying factors that affect the virus' transmission between birds. This includes the genetic and molecular adaptation that enables the virus to be transmitted from waterfowl and other migratory birds to domestic poultry.

Vaccine: USDA scientists are developing enhanced vaccines for birds against avian influenza.


Eating properly handled and cooked poultry is safe. If HPAI were detected in the U.S., the chance of infected poultry entering the human food chain would be extremely low. Proper handling and cooking of poultry provides further protection against this virus, as it does against many viruses and bacteria, including Salmonella and E.coli. Safe food handling and preparation is important at all times. USDA recommendations:

Poultry products imported to the U.S. must meet all safety standards applied to foods produced in the U.S. No poultry from countries with confirmed cases of H5N1 HPAI can be imported into the United States.


For more information about USDA's avian influenza efforts, go to http://www.usda.gov/birdflu.

More information about safe food preparation is available by calling the USDA Meat and Poultry Hotline at 1-888-MPHotline (1-888-674-6854).

More information about the federal government's efforts to protect human health is available at http://www.pandemicflu.gov/.