At least 40 people in Beijing have been diagnosed as suffering from a parasite-induced form of meningitis after eating raw or semi-raw snails at restaurants.

It is the first time the so-called Guangzhou angiostrongylus meningitis strain has been found in Beijing, according to the Beijing Municipal Health Bureau's website.

The first case, involving a 34-year-old man, was reported by Beijing Friendship Hospital (BFH) in June.

The patient suffered from unbearable headaches and nausea after eating a dish of "cold snail meat" at Shuguo Yanyi Restaurant.

The dish was made from Amazonian snails and is popular in Beijing's Sichuan-style restaurants. Doctors took samples from the restaurant and found the parasite in two snails.

As of last Thursday, 23 cases had been reported by BFH and other hospitals in the capital since May, according to the bureau.

The patients had all eaten cold or spicy snail meat. According to the bureau, five of the 23 were in a serious condition, three had been discharged, and two had apparently recovered without hospital treatment.

No deaths have been reported.

The youngest patient is a 13-year-old, who had a fever and a stiff neck a day after eating an Amazonian snail salad and a spicy snail dish in a branch of another restaurant chain called Sichuan Legend.

All 23 patients had consumed snails at two restaurants, both branches of Sichuan Legend. Doctors suspect a contaminated batch of Amazonian snails was the cause.

According to Xu Rongman, a researcher with the Institute of Microbiology and Epidemiology under the Academy of Military Medical Sciences, each Amazonian snail acts as an intermediate host of 3,000 to 6,000 parasites, which can harm the human nervous system, resulting in headaches, facial paralysis, meningitis and fever.

The Beijing Office of Food Safety issued an urgent notice on Saturday, calling for tighter supervision over aquatic products and safety inspection in supermarkets, shopping malls and restaurants. The office also warned people against eating raw fish, shrimp, snail, crab, frog and snake.

The snails have also been blamed for killing crops on more than 160,000 hectares in southwest China's Guangxi Zhuang Autonomous Region.

The Amazonian snail, also known as "Fushou snail" in China, was introduced in south China in the 1980s as a delicacy. However, the snails bred rapidly and infiltrated lakes, brooks and ponds, spelling disaster for local farmers because the snails ate every seedling in the rice fields and stole bait from carp in fishponds.

Moreover, the snail is highly resistant to toxic pesticides. Farmers have to pick them up by hand and move them far from water so that they shrivel to death or bury them. But such labor-intensive methods have proven ineffective. Having run out of options, farmers are appealing to scientists to find or breed a natural enemy of the snail.

After local media reported the news, BFH received more than 90 people at the weekend, all worried that they might have contracted illnesses having eaten snail dishes in the past two months.

Shuguo Yanyi has stopped serving the snail dish, and diners are generally refusing to eat Amazonian snails. "After I heard that Fushou snail could lead to meningitis, I decided not to order this dish any more," said Wang Yingchao, 34.

According to the bureau, other seafood might also contain parasites but the Amazonian snail has the ability to host more than others.

(China Daily, Xinhua News Agency August 21, 2006)