Bird flu spread around world by poultry trade, researchers say
Human commercial activities, and not migratory birds, are the driving force behind the global spread of bird flu, a team of French researchers argues in the British Ornithologists' Journal, Ibis. While acknowledging that wild birds contribute to the local spread of the disease in the wild, human activities, particularly the trade in poultry and poultry-related products, are the 'major factors' that have caused the disease to spread around the world, the scientists say. The virulent H5N1 strain of bird flu first arose in the late 1990s, but it did not start to spread until 2003, when it became widespread in southeast Asian poultry farms. In the early years, the spread of H5N1 was attributed to the movement of poultry and related products by people. However, in Spring 2005 hundreds of wild, migratory birds died of bird flu at Lake Quinghaihu, on the high Asian plateau in China. The researchers point out that in fact the species affected had arrived in China from uninfected areas, and the spread of the disease corresponds closely to human trade routes, not bird migratory routes. Nevertheless, this event started a trend of blaming migratory wild birds for the spread of the disease. The researchers also point to several flaws in the theory that bird flu's spread is driven by migrating birds. Referring to the spread of the disease from China to Europe, they point out that it took the virus several months to complete this journey, whereas migratory birds travel fast, covering several hundred kilometres in a single day. 'If migrating birds mainly dispersed the virus, the virus should also spread by large jumps of thousands of kilometres, throughout the migratory stopping places of Asia and Africa,' the researchers write. 'The observed expansion has rather been by a progressive expansion from isolated outbreaks, the geographical pattern of which corresponds well with major routes and patterns of human commerce.' Further proof of the predominant role of trade in spreading the disease comes from Asian countries which are successfully managing the epidemic. 'In Taiwan, Japan and South Korea, the virus has disappeared. Control of trade and strong veterinarian surveillance were the keys to this success,' the paper states. 'At the same time, migratory birds continue to pass through these countries in Spring and in Autumn.' Summing up, the researchers state that, 'the natural globalisation of the exchanges of migratory birds seemed to hide the globalisation - without strict health control - of the exchanges of poultry as the accepted mechanism for disease spread.' The article closes with a warning, as the authors note that concerns about bird flu could see farmers bringing their birds inside and rearing them intensively, something which is in fact more likely to increase the risk of outbreaks. They recommend that farmers continue the current trend towards better animal welfare and free range agriculture. 'All the evidence suggests that maintaining these trends whilst controlling disease through strong veterinary scrutiny and control of trade is more likely to be a successful strategy,' the researchers conclude.
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