Invasive Fresh Water Snail, China

To the Editor: Pomacea canaliculata, an invasive freshwater snail native to South America, was first introduced as a food to Taiwan in1979 and then to Mainland China in 1981 (1). It adapted well to the environment, particularly to the southern parts of the Mainland, spreading rapidly to more than 10 provinces (Figure) and causing tremendous damage to agriculture and the ecosystem (1,2). Thousands of hectares of rice, vegetables, and other crops in these provinces were destroyed (2).

Figure.

Distribution of Pomacea canaliculata in China. The dark triangles indicate the regions where angiostrongyliasis outbreaks were reported due to ingestion of raw or undercooked P. canaliculata snails.

Even more alarming were the multiple outbreaks of a severe brain disease (angiostrongyliasis) in Taiwan that were linked to P. canaliculata (3,4). Angiostrongyliasis is caused by Angiostrongylus cantonensis, a lung nematode of wild rodents, commonly known as the rat lungworm. In Mainland China, epidemiologic evidence also indicates that P. canaliculata, because of its high susceptibility to A. cantonensis, is becoming the most important natural intermediate host for this parasite (5). Previously, other terrestrial snails like Achatina fulicia, and some species of slugs such as Philomycus bilineatus were regarded as the major intermediate hosts for A. cantonensis (6). Epidemiologic survey results from 1997 to 1999 demonstrated that 20.8%–69.4% of P. canaliculata were infected with A. cantonensis in some regions of Guangdong, Zhejiang, and Fujian Provinces (5). Even in provinces where the snail is not found, a high incidence and prevalence of infection occur because of its widespread distribution, high susceptibility to A. cantonensis, and growing popularity as a food. In 1997, 2002, and 2002, ingestion of raw or undercooked P. canaliculata meat led to 3 outbreaks of angiostrongyliasis infecting >100 patients (6,7). A 2006 outbreak in Beijing infected 131 persons (8). Based on the biologic characteristics of P. canaliculata, blocking its life cycle is one of the most effective methods to limit the outbreak of angiostrongyliasis. However, the current widespread distribution of P. canaliculata in China and the lack of a highly effective control method make the disease extremely difficult to eliminate (9). More outbreaks associated with ingestion of this snail will likely occur if food safety rules are not strictly enforced. Citizens must also be educated to avoid eating raw, undercooked snail meat or raw vegetables from regions that may be contaminated with infective mucous trails deposited by these snails (10).