Mobile or migratory duck farming has been considered a culprit for spreading H5N1 around the Mekong delta as they move from province to province to feed on scattered grains after rice fields are harvested. That they’re free to roam around means they can come into contact with wild birds, and because ducks are fairly strong, sometime they can carry the virus without dying from it, hence spreading it to poultries along the way.
The co-existence of rice cultivation and duck farming in the Mekong delta probably existed since people started planting rice in the area. It’s a practice that benefits both rice and duck farmers. Duck farmers get free to cheap food to raise their flocks. Rice farmers get clean up services as the ducks come in and eat up all the pests in the field, and fertilize the fields with their poops! Apparently it’s not only applied in Vietnam but many other countries such as Southern China, the Philippines, India (Kerala).
What’s interesting is that this type of farming is a culture, an ingrained way of life. According to nongnghiep.vn, up to 2011 there are at least 30.9 million ducks in the Mekong delta and 27,000 family units engaged in duck farming (out of which 17,000 families still use migratory methods). Vaccination has really helped prevent mass outbreaks but the government cannot supply free vaccination forever, and people put their guards down if there are long periods of calm. Among other problems. surveillance is difficult because of constant movement and lack of incentive for farmers to report sickness.
People at OUCRU tell me while ducks farms are among the most interesting to set up cohort studies they’re a challenge to implement. The farmers move around too much. On top of that, if the number of ducks are too large owners cannot keep track, and if they’re too small people switch to farming other things depending on market demand, making a continuous study of 3 years seem impossibly long.