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The Relationship Between the Free-Grazing Duck System and Avian Influenza Persistence in Vietnam

28 March 2018

Prof. Dirk Pfeiffer (Chair Professor of One Health, CityU), led a team of researchers from the Royal Veterinary College (RVC) London, the Food and Agriculture Organization of the United Nations (FAO) and the National Institute for Animal Sciences and Ministry of Agriculture and Rural Development of Vietnam, in a study investigating avian influenza in free-grazing ducks in Vietnam.

Photo credit: © Anne Meyer,
Royal Veterinary College, University of London

It involved describing quantitatively the long-distance free-grazing duck production system in South Vietnam, characterising the movement and contact patterns of the duck flocks, and identifying potential associations between farming practices, movement and contact patterns and the circulation of avian influenza viruses. In addition, a value chain approach was used to provide a complete picture of the actors involved in the production and marketing of free-grazing duck eggs and spent layer ducks, as well as to investigate the governance structure of this food system.

Photo credit: © Anne Meyer,
Royal Veterinary College, University of London

Interviews among stakeholders involved in the free-grazing duck production system (duck farmers, transporters and rice paddy owners) were conducted and a virological cross-sectional survey in South Vietnam was carried out.

Results from the interviews show that both direct and indirect contacts between free-grazing duck flocks were frequent and diverse. The flocks were transported extensively across district and province boundaries, mainly by boat but also by truck or on foot. A third of the investigated flocks had a positive influenza A virology test, indicating current circulation of avian influenza viruses, but none were positive for H5 subtypes. The age and size of the flock as well as its location at the time of sampling were associated with the risk of influenza A circulation in the flocks.

The trade of spent layer ducks involved large volumes of live ducks being sent to China and Cambodia for consumption, generating a substantial risk of transboundary spread of pathogens, including HPAI viruses. So called “duck yards”, which act as hubs in the northbound trade of spent layer ducks play a major role and should be considered as essential links in the value chain of spent layer ducks when considering surveillance and control of the highly pathogenic avian influenza.

These findings are important when developing risk assessment models of influenza virus spread aimed at informing the development of improved biosecurity practices leading to enhanced animal health, sustainable animal production and reliable income for farmers.

This research was published in two papers: ‘Movement and contact patterns of long-distance free-grazing ducks and avian influenza persistence in Vietnam' in PLOS One ( and ‘Trade patterns facilitating highly pathogenic avian influenza virus dissemination in the free-grazing layer duck system in Vietnam’ in Transboundary and Emerging Diseases (