Influenza A virus subtype H5N1, also known as A(H5N1) or H5N1, is a subtype of the
Influenza A virus that is capable of causing illness in many animal species, including
humans.[1] A bird-adapted strain of H5N1, called HPAI A(H5N1) for "highly pathogenic
avian influenza virus of type A of subtype H5N1", is the causative agent of H5N1 flu,
commonly known as "avian influenza" or simply "bird flu" and is endemic in many bird
populations, especially in Southeast Asia. One strain of HPAI A (H5N1) of Asian lineage is
spreading globally. It is epizootic (an epidemic in non-humans) and panzootic (a disease
affecting animals of many species, especially over a wide area), killing tens of millions of
birds and spurring the culling of hundreds of millions of other birds in an attempt to control
its spread. Most references in the media to "bird flu" and to H5N1 are about this specific
strain.[2]
HPAI A(H5N1) is an avian disease, and there is no evidence of efficient human-to-human
transmission or of airborne transmission of HPAI A (H5N1) to humans. In almost all cases,
those infected with H5N1 have had extensive physical contact with infected birds.
However, around 50% of humans known to have been infected with the current Asian
strain of HPAI A(H5N1) have died from H5N1 flu, and H5N1 has the potential to mutate or
re-assort into a strain capable of efficient human-to-human transmission. On September
29, 2005, David Nabarro, the newly-appointed Senior United Nations System Coordinator
for Avian and Human Influenza, warned the world that an outbreak of avian influenza could
kill anywhere between 5 million and 150 million people.[3] Experts have identified key
events (creating new clades, infecting new species, spreading to new areas) marking the
progression of an avian flu virus towards becoming pandemic, and many of those key
events have occurred more rapidly than expected.
References
1 International Committee on Taxonomy of Viruses (2002). 46.0.1. Influenzavirus A.
Retrieved on 2006-04-17.
2 a b Li KS, Guan Y, Wang J, Smith GJ, Xu KM, Duan L, Rahardjo AP, Puthavathana P,
Buranathai C, Nguyen TD, Estoepangestie AT, Chaisingh A, Auewarakul P, Long HT,
Hanh NT, Webby RJ, Poon LL, Chen H, Shortridge KF, Yuen KY, Webster RG, Peiris JS.
(2004). "Genesis of a highly pathogenic and potentially pandemic H5N1 influenza virus in
eastern Asia". Nature 430 (6996): 209-213. PubMedDOI:10.1038/nature02746.
3 United Nations. "Press Conference by UN System Senior Coordinator for Avian, Human
Influenza", UN News and Media Division, Department of Public Information, New York,
2005-09-29. Retrieved on 2006-04-17.