The role of moving duck flocks in the spread of Highly Pathogenic Avian Influenza (HPAI) virus in Vietnam and Indonesia

Moving or nomadic duck flocks in SE-Asia are flocks that are frequently transported to areas where they can find suitable feed, in particular in rice paddies after the harvest. Using rapid rural appraisal methods we interviewed moving duck owners in the Mekong Delta of Viet Nam and in Central Java of Indonesia to describe their management system. The characteristics of the moving duck production system appear to be conducive to these ducks spreading and transmitting HPAI virus to other birds: 1) Flocks are moved frequently and quickly over large distances, 2) Flocks use many different scavenging areas, 3) Flocks are exposed to numerous HPAI risk factors, such as having contact with other scavenging ducks, wild birds and domestic animals, and 4) A large number of people are involved in transport and management of these flocks. In Viet Nam, movement of ducks is usually conducted with boats and trucks over long distances (median distance travelled per year: 80km) throughout most of the year (travel duration per year: 30-285 days), while in Indonesia flocks travel shorter distances during just a few months of the year and are transported on motorbikes, cars or herded by foot. Moving duck flocks in Viet Nam are larger than in Indonesia and are usually moved as single flocks owned by only one farmer, whereas in Indonesia, flocks of several owners often share transport. In additional field studies, 48 Vietnamese and 54 Indonesian moving duck flocks were monitored over a period of 6 months with blood samples being collected from individual birds. Overall crude bird-level HPAI H5 antibody prevalence (HI titre≥16) was about 15.5% in Viet Nam and 5.3% in Indonesia