Highly Pathogenic Asian Avian Influenza A (H5N1) Virus
Asian 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 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 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 virus (a reassortant) that is genetically different from the Asian 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 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.