Dispersal and evolution of the invasive snail Pomacea canaliculata, an intermediate host of Angiostrongylus cantonensis: A field study around its initial introduction site in China

Eosinophilic meningitis caused by Angiostrongylus cantonensis is an emerging infectious disease in mainland China. The invasive snail (Pomacea canaliculata) is one of the main intermediate host of the zoonotic nematode. To gain insights into the spatial distribution, phenotypic variation and dispersal pattern of the snail populations. A field survey was conducted using modified nested sampling and selecting ditches as the main habitats. Snail distribution and abundance were displayed with predictions based on an inverse distance-weighted model. Correlation and spatial autocorrelation were analyzed among the measured parameters. The findings of this study demonstrate the well-established and abundant presence of P. canaliculata in ditches. A total of 564 sampling sites were assessed, with measurements taken on 10,145 snails having shell heights greater than 1.5 cm. The average population density was determined to be 20.31 {+/-} 11.55 snails per square meter. Morphological analysis revealed an average snail body mass of 8.93 {+/-} 3.95 g, shell height of 3.38 {+/-} 0.66 cm, a sex ratio of 2.39 {+/-} 1.01 female to male, and a shell color ratio of 9.34 {+/-} 7.52 brown to yellow. Among these measurements, body mass was found to be significantly correlated with shell height (r = 0.88, p < 0.01) and shell color (r = 0.55, p < 0.05). Spatial-correlation analysis proved that shell height was the only factor significantly spatially autocorrelated (MI = 0.27, z = 2.20, p = 0.03), although weak autocorrelations appeared in body mass and shell color. The observed geographic variations of phenotypic traits indicated a human-mediated evolving process of the snail populations and a potential complexity of the parasite transmission system. These findings may enhance the assessment of the epidemiological health risk posed by angiostrongyliasis and inform strategies for controlling infectious snails.