In a smoky brick shed atop a bank between fish ponds, Yang Jian, a stocky woman wearing red plastic gumboots, squats by a bubbling cauldron of brown slop and pokes the coal fire underneath.

"It's leftovers from restaurants, and sometimes it's already gone off, so we boil it up to make it sterile," she says. Pointing to plastic sacks in a corner, she adds "We mix in corn and wheat flour for extra body."

The customers for this meal live in a four-meter enclosed pen next door. Eleven glistening snouts and pairs of eyes come toward an approaching human. The young pink and white pigs collapse in a sighing, grunting heap when no slop is poured into the concrete trough.

Mrs. Yang and Wen Qing, a fellow pig farmer calling by for a chat, say the pigs occasionally develop a shortness of breath from chilli, and tend to catch colds in changes of weather. "We give them an injection," said Mr Wen. "We just buy the antibiotics like penicillin in town. We usually don't call a vet, we know from our own experience what to inject."

In this village called Dongxing on the fringes of Foshan city, rural and industrial China live side by side. Dongxing's 700 residents live in a tight settlement of newish, three-storey townhouses and flats surrounded by a belt of fish ponds and neat market gardens. But most of their wealth comes from selling and letting more distant land for factories and apartments, visible on all sides.

Foshan, a city of more than 3 million people, is one of the specialized manufacturing cities that make southern China's Guangdong province a workshop for the world. Foshan is probably the global bathroom and toilet capital, with street after street of showrooms full of porcelain and ceramic wares.

But currently it is more noted for another possible export. It was here, mid-November, that the first known case of the lethal pneumonia called severe acute respiratory syndrome (SARS) has been pinpointed. The Chinese public servant who came down with it recovered, but infected four other people and the disease has since spread worldwide, claiming 82 lives.

Guangdong and the nearby autonomous former British colony of Hong Kong, however, have been hardest hit, and the SARS epidemic has refocused attention on this region's record as a source of devastating new epidemics of influenza, including possibly the "Spanish flu" which swept the world in 1918-19 killing over 20 million people.

Dongxing is just one example of how Guangdong's 80 million people live close to the animals, poultry and fish they eat. At another piggery close to Mrs. Yang's, a farmer keeps young chickens next to his pigs. All the piggeries empty their waste into the ponds where shrimp and grass-carp are raised for the table.

In other places, battery chickens are kept above the pig pens, feeding their waste into the pigs' food troughs. The close proximity and cross pollution adds to the risk of animal viruses infecting humans, either directly or via pigs

"It's a complete soup of chemicals and viruses," says Christine Loh, a former legislator and head of the Hong Kong think-tank Civic Exchange, who is one of the city's leading analysts of environmental questions.

She says little has been done since an epidemic of avian flu hit Hong Kong in 1997. This flu variety jumped from poultry to humans, affecting hundreds of Hong Kong residents and killing six. Health authorities ordered the slaughter of 1.5 million chickens and ducks to prevent it spreading further.

The avian flu did not transmit between humans, making the killing of the bird hosts a preventative option. But the nightmare anticipated by the World Health Organization is for a lethal new disease like SARS to combine with genetic sequences from an influenza virus in the cells of a host with both infections, and create a new pandemic on the scale of 1918.

In Nanzhuang, another town in Guangdong, Fu Dewu keeps ducks for their eggs in a corner of land above a fish pond, camping with fellow workers in a corner of the bamboo and tar paper shanty where the ducks roost. Mr. Fu says he has never been visited by health officials to be given any guidance on safe practices.

He lost half his 5000 stock of ducks to a second wave of avian flu in 1999. The affected birds were not slaughtered, however. "Some people came from Shenzhen [the export city next to Hong Kong] and took the infected birds away in their truck," he said. "They were going to sell them for meat. People have no scruples around here. Only money counts."

Farmers like those in Dongxing have free access to antibiotics that officially require a doctor or vet's prescription, adding to the risk of dangerous bacteria developing immunity to the drugs. Even in the provincial capital Guangzhou, one of China's largest cities, antibiotics are freely sold over the counter along with traditional herbal remedies.