As Mt Merapi, Indonesia’s most active volcano, spews out smoke and lava, a disaster is incubating in the farms and villages of Central Java with potentially far greater consequences for human health.

In the nearby Ambarawa livestock market, Joko, a local farmer, laughs at the risk of bird flu as he runs his hand lovingly over the rear of his prize black chicken. Ducks and other birds for sale mill nearby, feathers drift in the air and their dung cakes the ground. When one of his birds gets sick, he says, he sucks the mucus from its beak with his mouth.