HONG KONG, July 10 (Reuters) - Thai researchers have urged people in Southeast Asia to stop eating raw freshwater fish because they risk becoming infected with a parasitic worm that may predispose them to developing liver cancer.

At issue are parasitic worms, commonly known as fluke, which infest rivers in rural parts of Thailand, Vietnam, Laos, Cambodia, Korea and China. The worms find their way into freshwater fish, and into humans when the fish is consumed raw.

Writing in the latest issue of the Public Library of Science journal PLoS Medicine, the researchers said most people infected with fluke showed no symptoms but some went on to develop liver cancer years later.

"Less than 1 percent who are infected with fluke will get liver cancer, but those who get infected are in the millions in Thailand, Cambodia and Vietnam. There are 6 million (infected with fluke) in Thailand," said Banchob Sripa of the pathology department in Thailand's northern Khon Kaen University.

Banchob has studied the link between fluke infection and liver cancer, particularly in the bile duct, for more than 20 years.

He and his colleagues found fluke infection to be especially serious in the north and northeastern provinces of Thailand, where a raw fish dish, called Koi-Pla, is popular.

"Stop eating this, it's the easiest thing to do," Banchob said in a telephone interview.

He said fluke attack the human bile duct and the incursion triggers a "cytokine storm" -- an immune response so intense that it destroys not only the parasites, but the person's surrounding tissues as well.

"There are two mechanisms. The fluke has two suckers. It can bite the surface epithelium of the bile duct and cause ulcers. The second is the inflammation," Banchob said.

"The ones with more inflammatory cytokines may have more inflammation ... and these may develop cancer later on."

Liver cancer is usually diagnosed when it is far advanced because symptoms surface late.

"Most who are diagnosed have advanced cancers, like stage 4, so they only get palliative care. It is very difficult to detect early lesions because there are no symptoms," he said.

Most deaths occur within six months to a year of diagnosis. "There would be zero survivors after five years," he said.

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