Introduction
It has long been known that wild birds represent a reservoir for low pathogenic avian influenza (LPAI) viruses worldwide but to date, wild birds have not been identified as the reservoir for the H5N1 highly pathogenic avian influenza (HPAI) strain that has resulted in the rapid spread of this disease across Asia into Europe and Africa from 2005 onwards in domestic poultry, wild birds, and humans.
This virus is unique among the Avian Influenza viruses in that it has killed thousands of wild birds, resulted in over 200 human deaths, resulted in death or destruction of millions of domestic poultry, impacted negatively on people's livelihoods, commerce and trade, and eliminated a protein source of many people in developing and developed countries. This demonstrates the importance of understanding the ecology of this disease and the interphase between domestic and wild avian species.
Land-use changes resulting in farms and wetlands being closer to one another, and open grazing of poultry in rice fields and wetlands shared with wild birds creates mechanisms for transmission of viruses amongst these sectors. As well, spreading of infected manure as fertilizer, or water run-off from infected farms into natural habitats may also explain possible mechanisms by which disease moves from poultry production operations or households into wild bird habitats.
The unusual outbreak of H5N1 HPAI in wild migratory birds in China in 2005 which lead to the death of over 6,000 wild birds and the rapid geographic spread thereafter into West Asia , Europe and Africa has resulted in the need to carefully evaluate the role of wild birds in maintaining and spreading the H5N1 HPAI virus. While it is known that the legal and illegal trade of poultry and poultry products, or unintentional movement of the virus by humans are the primary sources of disease movement, the extent to which free flying wild birds contribute to sustaining and spreading the disease needs to be determined.
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