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    BEIJING, Aug. 20 (Xinhua) -- Twenty-three people in Beijing have fallen ill since May after eating snails, according to the Beijing Health Bureau.

    Eighteen are still in hospital - five of them are seriously ill. The other five have made a complete recovery.

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

    All the patients had eaten the snails in two restaurants, both branches of Sichuan Legend. Doctors suspect that a batch of the Amazonian snails was contaminated.

    According to Xu Rongman, researcher with the Institute of Microbiology and Epidemiology under the Academy of Military Medical Sciences, each Amazonian snail is an intermediate host of 3,000 to 6,000 parasites, which can harm the human nervous system, leading to 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.

    Amazonian snails originate from South America and first came to China in the 1980s. The first patient of Angiostrongylus Cantonensis, the disease caused by the snails, was reported in Guangzhou, capital city of south China's Guangdong Province. Enditem

Backgrounder: Amazonian snail

    Amazonian snail which is dubbed "Fushou snail" in China, was introduced to the southern county in the 1980s as a food delicacy. However, the snails bred very rapidly to infiltrate all lakes, brooks and ponds in the whole county - a disaster for local farmers as they tended to eat every seedling in the rice fields and seize bait from carp in fishponds.

    Making matters worse, the Amazonian snail is strongly resistant to highly toxic pesticides. Farmers have to pick them up by hand and take them far from water so they shrivel to death or directly bury them. But such labor-intensive methods have proved ineffectual against the powerful potency of the river snails. Having run out of options, the farmers are appealing to scientists to find or breed a natural enemy of the river snail.