Discussion
The intermediate host snail
Oncomelania was collected widely in China, and schistosomes were recovered by infecting mice with cercariae released from snails. Initially, ITS sequences, and several fragments of mitochondrial regions were employed for investigating the genetic diversity of the snail and the parasite. No shared haplotypes were found for snails distributed in the upper reaches and in the middle and lower (ML) reaches, nor for the parasites in these two regions. The genetic diversity of 66 populations of
O. hupensis was further examined using microsatellite markers. The average number of alleles was 10, and 40 populations and 3 loci were significantly deviated from Hardy�Weinberg equilibrium. The pair-wise
FST value ranged from 0.061 to 0.759 among populations, indicating great differentiation in populations. Populations from Yunnan Province were the most distant from others; populations from Sichuan province were clustered together as a separate branch. Populations from Fujian and Taiwan were genetically distinct from those collected in Guangxi and ML reaches. Furthermore, 66 populations were divided into five groups, as revealed through the analysis of molecular variance (AMOVA), including Yunnan, Sichuan, Fujian, Taiwan, ML and Guangxi groups. The Mantel test revealed a significant positive correlation between genetic distance
FST and geographical distance, indicating an isolation-by-distance effect on the differentiation of
O. hupensisin, with some populations undergone bottle-neck effect. Mitochondrial genomes were sequenced from 9
geographic strains of
S. japonicum in China, and the constructed phylogenetic relationship showed that the Taiwan strain and strains from Yunnan and Sichuan Pronvinces and those in the ML reaches were grouped separately.
