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).


Invasive Freshwater Snail, China
To the Editor: Pomacea canaliculata, an invasive freshwater snail native to South America, was fi rst 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).
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 diffi cult 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).
A total of 203 cloacal swab samples were positive for infl uenza A virus matrix gene when tested by real-time PCR, and 2 were also positive for the hemagglutinin 5 (H5) gene by using specifi c primers (7). Of the 2 migratory birds positive for the H5 gene, the fi rst was a common teal (Anas crecca) captured in the Nile Delta region of Damietta in October 2005 (online Appendix Figure, panel A). Sequenc-ing of the H5 gene showed that this virus was an LPAI most closely related to strain A/mallard/Bavaria/1/ 2005(H5N2) (GenBank accession no. DQ387854 (2).
In January 2006, an infl uenza A H5 virus (weak positive result) was detected in another common teal (trapped in a cage by a fi sherman) sampled from the Damietta region in December 2005 (online Appendix Figure, panel A). The low viral load, coupled with the failure to isolate the virus, precluded the laboratory from conducting sequence analysis at the time on the basis of insuffi cient template material. After the outbreak of infl uenza A (H5N1) in poultry and humans in Egypt in February 2006, additional retrospective attempts to concentrate RNA were used to assess potential introduction scenarios. After multiple RNA extractions were conducted and the RNA was concentrated, this specimen was found to be positive for the neuraminidase 1 (N1) gene by real-time PCR.
The hemagglutinin gene from both teal strains was sequenced (≈1,596 bp). Sequences were aligned with other infl uenza A (H5N1) strains from Egypt (9 from humans, 5 from chickens). Twenty other strains with high similarity and from different locations were selected by using a Gen-Bank search algorithm and included in the alignment. A phylogenetic analysis was conducted by using the Kimura 2-parameter model. The LPAI H5 virus strain was used as an outgroup in a neighbor-joining phylogenetic tree. Bootstrap analysis with 500 replicates of sequence data was also conducted by using MEGA 3.1 software (8).
Phylogenetic analysis showed clustering of the HPAI (H5N1) strains collected from 1 geographic region (country) (online Appendix Figure, panel B). All HPAI (H5N1) strains from Egypt from humans or chickens analyzed clustered with a bootstrap support value of 98%. Furthermore, the A/Teal/Egypt/14051-NAMRU3/2006