Invasive Snails and an Emerging Infectious Disease: Results from the First National Survey on Angiostrongylus cantonensis in China

Abstract

Background

Eosinophilic meningitis (angiostrongyliasis) caused by Angiostrongylus cantonensis is emerging in mainland China. However, the distribution of A. cantonensis and its intermediate host snails, and the role of two invasive snail species in the emergence of angiostrongyliasis, are not well understood.

Methodology/Principal Findings

A national survey pertaining to A. cantonensis was carried out using a grid sampling approach (spatial resolution: 40×40 km). One village per grid cell was randomly selected from a 5% random sample of grid cells located in areas where the presence of the intermediate host snail Pomacea canaliculata had been predicted based on a degree-day model. Potential intermediate hosts of A. cantonensis were collected in the field, restaurants, markets and snail farms, and examined for infection. The infection prevalence among intermediate host snails was estimated, and the prevalence of A. cantonensis within P. canaliculata was displayed on a map, and predicted for non-sampled locations. It was confirmed that P. canaliculata and Achatina fulica were the predominant intermediate hosts of A. cantonensis in China, and these snails were found to be well established in 11 and six provinces, respectively. Infected snails of either species were found in seven provinces, closely matching the endemic area of A. cantonensis. Infected snails were also found in markets and restaurants. Two clusters of A. cantonensis–infected P. canaliculata were predicted in Fujian and Guangxi provinces.

Conclusions/Significance

The first national survey in China revealed a wide distribution of A. cantonensis and two invasive snail species, indicating that a considerable number of people are at risk of angiostrongyliasis. Health education, rigorous food inspection and surveillance are all needed to prevent recurrent angiostrongyliasis outbreaks.

Author Summary

Eosinophilic meningitis is caused by the rat lungworm ( Angiostrongylus cantonensis). This parasite is endemic in Southeast Asia, Australia, the Caribbean, and on Pacific Islands. Moreover, the disease is emerging in mainland China, which might be related to the spread of two invasive snail species ( Achatina fulica and Pomacea canaliculata). Thus far, the biggest angiostrongyliasis outbreak in China occurred in 2006 in Beijing, involving 160 patients. However, detailed information about the national distribution of A. cantonensis and its intermediate hosts is still lacking, and the importance of the two invasive snail species for disease transmission is not well understood. Therefore, a national survey on the distribution of A. cantonensis and its intermediate hosts in China was carried out in 2006/2007. It was found that A. fulica and P. canaliculata were implicated in most angiostrongyliasis outbreaks, and that the distribution of A. cantonensis closely matched that of these snails. The two invasive snail species facilitated the expansion of the parasite, thus probably leading to the emergence of angiostrongyliasis, a previously rare disease, in mainland China.