Do wild birds spread the flu?

From the BBC, March 1, 2006

Dr Leon Bennun, Director of Science, Policy and Information for BirdLife International, questions the view that avian influenza in spread by migratory birds, and proposes instead that the culprit is the poultry trade.

In evidence he points out that the timing and pattern of outbreaks of the deadly H5N1 strain of avian influenza often follow trade, and not migration, routes. Some flight paths in Asia remain flu-free, and countries such as Japan and Korea, which imposed strict controls on infected farms have curbed further spread.

Dr Bennun notes that the crowded conditions on intensive farms with constant exposure to feces and saliva are ideal for the evolution of highly lethal viral strains through selection, replication, mutation and recombination. A recent analysis of viral strains (published in the Proceedings of the National Academy of Sciences, USA) supports the view that poultry movements have played a major role in spreading the current epidemic.

Lethal flu strains are rare in wild birds and normally burn out without human intervention. It seems probable that the dead swans found in western Europe acquired the H5N1 infection before they migrated, from grazing in fields fertilized with infected poultry manure.

Dr Bennun suggests that, for economic reasons, agencies such as UN-FAO are reluctant to blame intensive agriculture. As a result, the role of wild birds has been exaggerated and sensationalized in the media. Demands for culling, destruction of nesting sites and draining wetlands may endanger rare species, while not alleviating the problem on the farm.

BirdLife International is calling for an independent inquiry to ensure that the right questions are asked, so that effective measures can be taken to protect the health of humans and animals, as well as biodiversity in the environment.