Avian Influenza Basics

Avian Influenza Basics

Avian Influenza Basics

Worldwide, there are many strains of avian influenza (AI) virus that can cause varying degrees of clinical illness in poultry. AI viruses can infect chickens, turkeys, pheasants, quail, ducks, geese and guinea fowl, as well as a wide variety of other birds. Migratory waterfowl have proved to be a natural reservoir for the less infectious strains of the disease.

AI viruses can be classified as highly pathogenic (HPAI) or low pathogenic (LPAI) strains based on the severity of the illness they cause. HPAI is an extremely infectious and fatal form of the disease that, once established, can spread rapidly from flock to flock and has also been known to affect humans.  LPAI typically causes only minor illness, and sometimes manifests no clinical signs.  However, some LPAI virus strains are capable of mutating under field conditions into HPAI viruses.

USDA’s Animal and Plant Health Inspection Service (APHIS) works to keep HPAI from becoming established in the U.S. poultry population.

Avian Influenza Response

The United States has the strongest AI surveillance program in the world.  As part of the existing USDA avian influenza response plans, Federal and State partners as well as industry are responding quickly and decisively to these outbreaks by following these five basic steps: 1) Quarantine – restricting movement of poultry and poultry-moving equipment into and out of the control area; 2) Eradicate – humanely euthanizing the affected flock(s); 3) Monitor region – testing wild and domestic birds in a broad area around the quarantine area; 4)  Disinfect – kills the virus in the affected flock locations; and 5) Test – confirming that the poultry farm is AI virus-free.  USDA also is working with its partners to actively look and test for the disease in commercial poultry operations, live bird markets and in migratory wild bird populations. 

USDA will include the confirmation information in routine updates to the World Organization for Animal Health (OIE), and will notify international trading partners of this finding as appropriate.  OIE trade guidelines call on countries to base trade restrictions on sound science and, whenever possible, limit restrictions to those animals and animal products within a defined region that pose a risk of spreading disease of concern.

These virus strains can travel in wild birds without them appearing sick. People should avoid contact with sick/dead poultry or wildlife. If contact occurs, wash your hands with soap and water and change clothing before having any contact with healthy domestic poultry and birds.

USDA emphasizes that poultry, poultry products and wild birds (see biosecurity and wild birds) are safe to eat if they are properly handled and cooked to a temperature of 165 degrees Fahrenheit.

All bird owners, whether commercial producers or backyard enthusiasts, should continue to practice good biosecurity, prevent contact between their birds and wild birds, and report sick birds or unusual bird deaths to State/Federal officials, either through their state veterinarian or through USDA’s toll-free number at 1-866-536-7593.  Additional information on biosecurity for backyard flocks can be found at http://healthybirds.aphis.usda.gov.

Background Information

The H5N8 virus originated in Asia and spread rapidly along wild bird migratory pathways during 2014, including the Pacific flyway.  In the Pacific flyway, the H5N8 virus has mixed with North American avian influenza viruses, creating new mixed-origin viruses.  This is not unexpected.  These mixed-origin viruses contain the Asian-origin H5 part of the virus, which is highly pathogenic to poultry.  The N parts of these viruses came from North American low pathogenic avian influenza viruses.

USDA has identified two mixed-origin viruses in the Pacific Flyway: the H5N2 virus and new H5N1 virus.  The new H5N1 virus is not the same virus as the H5N1 virus found in Asia that has caused some human illness.  CDC considers the risk to people from these HPAI H5 infections to be low.  Detailed analysis of the virus is underway in cooperation with CDC.



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