Disease watchdogs in northeast China's Heilongjiang Province yesterday warned people not to eat raw freshwater products in order to avoid the parasite-caused disease clonorchiasis.

A recent survey by the Heilongjiang Provincial Center for Disease Control and Prevention estimated that more than 1.5 million people living near rivers in the province might have the disease, said Ji Zhuo, director of the parasite disease institute at the center.

The overall incidence of clonorchiasis in the province is about 4.7 percent, which means more than 1.5 million people out of a population of 38 million may have the disease, Ji said. A reason for the huge number could be that more people are in the habit of eating raw aquatic products, he added.

The news comes as medical authorities nationwide warned about the danger of eating raw or undercooked freshwater seafood to prevent diseases caused by parasites.

The warning came after 70 people in Beijing were found to be suffering from meningitis after eating the Amazonian snail. Many said they might sue for compensation.

Improper cooking or the eating of raw snails, which failed to kill the Angiostrongylus cantonesis, a parasite in the snail, were believed to have caused the disease in the capital.

Ji in Heilongjiang said spot checks showed a higher percentage of clonorchiasis in some places.

The province's Zhaoyuan County, where two major rivers meet, had the highest incidence of the disease.

Five hundred people were picked at random; about 200 were found to be infected with the parasite.

"Even allowing for errors, the rate is still about 30 to 40 percent," Ji added. "And even if we go with 30 percent, that still means 120,000 people out of the 400,000-plus people in Zhaoyuan may have been infected," Ji said.

In humans, the parasite lives in the duct connecting the liver and bile cyst.

Preliminary symptoms of the disease are vomiting, fatigue and aching. In severe cases, liver cancer and other serious conditions can develop.

"Some people may feel uncomfortable immediately while some may find the disease 10 or 20 years later, when it is too late," said Ji, adding that more than 10,000 of the parasite's spawn were found in one man.

Ji suggested that people who have eaten raw or undercooked freshwater products get a medical check as soon as possible.

He said more people were getting the disease "mainly because more people have begun to eat raw fish."

Nationwide, clonorchiasis is listed as one of the key parasite-caused diseases in China. In 2004 the government estimated that more than 12 million people could be affected.

The Pearl River Delta and northeast China are the two major areas for it.

An estimated 5 million people in Guangdong were reported by local media to have the disease last year.

Meanwhile, in Beijing, hospitalized patients diagnosed with meningitis after eating parasite-infested snails in a Beijing restaurant said they might sue for compensation.

The Xinhua News Agency quoted a patient surnamed Zhang as saying he had spent 20,000 yuan (US$ 2,500) on treatment.

"Patients have discussed jointly making a claim for medical expenses and compensation for lost work and emotional suffering," he said.

(China Daily August 23, 2006)