Ban Phai, Mancha Khiri and Channabot, which are all in the Shi River basin, are known as "the world's cholangiocarcinoma basin", said Professor Banjob Sripha, of the pathology division of the university's faculty of medicine.

Cholangiocarcinoma is a rare cancer of the bile ducts that can be caused by trematodes (parasitic flatworms) inhibiting liver functions.

More than six million people in Thailand, or 9.4 per cent of the population, have trematodes as a result of the long-standing habit in the Northeast of eating uncooked meat and fish. Of the six million, 97 per cent live in the poverty-stricken region. In the Northeast, 39 people per 100,000 suffer from cholangiocarcinoma. That figure triples to around 118 per 100,000 in the three Khon Kaen districts.

The figure is much lower in other regions - 15 in the North, Central and Bangkok and only 1.5 in the South.

The study, funded by a Bt24-million grant from the US National Institute of Health, revealed that trematodes were found in a two-year-old baby. Banjob said the only possible cause was that his parents fed him uncooked meat or fish.

In its terminal stage, cholangiocarcinoma mostly results in death within three months. The most effective treatment before the cancer develops is to remove each trematode from the liver through surgery.

The number of trematodes in a person can range from 100 to 1,000.