Risks of avian influenza transmission in areas of intensive free-ranging duck production with wild waterfowl
For decades, southern China has been considered to be an important source for emerging influenza viruses since key hosts live together in high densities in areaswith intensive agriculture. However, the underlying conditions of emergence and spread of avian influenza viruses (AIV) have not been studied in detail, particularly the complex spatiotemporal interplay of viral transmission between wild and domestic ducks, two major actors of AIV epidemiology. In this synthesis,we examine the risks of avian influenza spread in Poyang Lake, an area of intensive free-ranging duck production and large numbers of wild waterfowl. Our synthesis shows that farming of free-grazing domestic ducks is intensive in this area and synchronizedwithwild duckmigration. The presence of juvenile domestic ducks in harvested paddy fields prior to the arrival and departure of migrant ducks in the same fields may amplify the risk ofAIV circulation and facilitate the transmission between wild and domestic populations. We provide evidence associating wild ducksmigration with the spread ofH5N1 in the spring of 2008 from southern China to South Korea, Russia, and Japan, supported by documented wild duck movements and phylogenetic analyses of highly pathogenic avian influenza H5N1 sequences.Wesuggest that preventionmeasures based on amodification of agricultural practicesmay be implemented in these areas to reduce the intensity of AIV transmission between wild and domestic ducks. This would require involving all local stakeholders to discuss feasible and acceptable solutions.