Highly Pathogenic Asian-Origin Avian Influenza A (H5N1) Virus
Asian-origin highly pathogenic avian influenza (HPAI) A (H5N1) virus occurs mainly in birds and is highly contagious among them. HPAI Asian H5N1 is especially deadly for poultry. The virus was first detected in 1996 in geese in China. Asian H5N1 was first detected in humans in 1997 during a poultry outbreak in Hong Kong and has since been detected in poultry and wild birds in more than 50 countries in Africa, Asia, Europe, and the Middle East. Six countries are considered to be endemic for Asian-origin HPAI H5N1 virus in poultry (Bangladesh, China, Egypt, India, Indonesia, and Vietnam).
Since its widespread re-emergence in 2003, rare, sporadic human infections with this virus have been reported in Asia, and later in Africa, Europe, and the Middle East. Human infections with Asian H5N1 viruses have been associated with severe disease and death. Most human infections with avian influenza viruses, including HPAI Asian-origin H5N1 viruses, have occurred after prolonged and close contact with infected birds. Rare human-to-human spread with this virus has occurred, but it has not been sustained and no community spread of this virus has ever been identified.
In January 2014, Canada reported the first human infection with HPAI Asian H5N1 virus in the Americas. This was an “imported” case occurring in a traveler who had recently returned from China. To date, there have not been any reports of HPAI Asian H5N1 virus infections in people in the United States and Asian H5N1 has never been detected in U.S. birds or poultry. (The H5N1 virus recently detected in U.S. wild birds is a new mixed-origin virus (a reassortant) that is genetically different from the Asian-origin avian H5N1 viruses).
Flu viruses are constantly changing and animal flu viruses can change such that they may gain the ability to infect people easily and spread among people, causing a pandemic. Human infections with novel avian influenza virus like Asian H5N1 are concerning because of this pandemic potential. CDC takes routine public health preparedness measures whenever a virus with pandemic potential is identified. Because Asian H5N1 continues to circulate and has been responsible for a number of human infections, Asian-origin H5 preparedness efforts have been extensive. Asian H5N1 vaccine is being stockpiled for pandemic preparedness by the United States government. It could be used if an HPAI H5N1 virus begins transmitting easily and efficiently from person to person.
- Interim Guidance on Case Definitions for Investigations of Human Infection with Highly Pathogenic Avian Influenza A (H5N1) Virus in the United States
- Interim Guidance for Laboratory Testing of Persons with Suspected Infection with Highly Pathogenic Avian Influenza A (H5N1) Virus in the United States
- Follow-up of Close Contacts of Persons Infected with Novel Influenza A Viruses Associated with Severe Human Disease and the Use of Antiviral Medications for Chemoprophylaxis
- Interim Guidance for Specimen Collection, Processing, and Testing for Patients with Suspected Infection with Novel Influenza A Viruses Associated with Severe Disease in Humans
- Interim Guidance for Infection Control Within Healthcare Settings When Caring for Confirmed Cases, Probable Cases, and Cases Under Investigation for Infection with Novel Influenza A Viruses Associated with Severe Disease
- Interim Guidance on the Use of Antiviral Medications for Treatment of Human Infections with Novel Influenza A Viruses Associated with Severe Human Disease
- Candidate vaccine viruses and potency testing reagents for influenza A (H5N1)
- Asian-origin H5N1 In Birds and Other Animals
- Asian-origin H5N1 In People
Risk to Human Health
- While the risk from Asian H5N1 is low to most people, CDC recommends general precautions.
- Sporadic human infections with Asian H5N1 virus have occurred in other countries, primarily in Asia and Africa. Most human infections with Asian H5N1 viruses in other countries have occurred after prolonged and close contact with infected sick or dead birds.
- No animal or human infections with Asian H5N1 virus have occurred in the United States.
- Travelers to countries with known outbreaks of Asian H5N1 influenza should avoid poultry farms, contact with animals in live food markets, and any surfaces that appear to be contaminated with feces from poultry or other animals.
- As a general precaution, people should avoid wild birds and observe them only from a distance; avoid contact with domestic birds (poultry) that appear ill or have died; and avoid contact with surfaces that appear to be contaminated with feces from wild or domestic birds.
- People who have had contact with infected bird(s) should monitor their own health for possible symptoms (for example, conjunctivitis, or flu-like symptoms). During your visit to an area affected by avian flu, seek medical care if you feel sick.
- People who have had contact with infected birds may also be given influenza antiviral drugs preventatively.
- Health care providers evaluating patients with possible HPAI Asian-origin H5N1 infection should notify their local or state health departments which in turn should notify CDC.
- Page last reviewed: April 27, 2015
- Page last updated: May 6, 2015
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