Genetic diversity and structure of Oncomelania hupensis hupensis in two eco-epidemiological settings as revealed by the mitochondrial COX1 gene sequences

Population structure and temporal variation of Oncomelania hupensis snails in a currently Schistosoma japonicum-eliminated area of China using microsatellite analyses

Schistosomiasis is the second most important tropical disease in terms of socio-economic and public health impact among human parasitic diseases. In China, Oncomelania hupensis is the only intermediate host of Schistosoma japonicum. Despite the significant progress made, the wide distribution of O. hupensis habitats remains a major challenge to eliminating S. japonicum across China. Therefore, it is important to understand the population genetics of O. hupensis in given environment in order to guide local snail control. In this study, O. hupensis snails were collected from five snail habitats/sites (i.e., DT, JC, XG, XP and YH) in Jiaxing city in Zhejiang province of China between 2022 and 2023, and population genetic analyses were conducted based on nine microsatellites. Results showed that four O. hupensis snail populations (i.e., JC, XP and YHs) from two proximity geographically distant districts clustered together, indicating genetic exchange. Snails collected in XG and YH showed significant temporal genetic variation between two years. However, bottleneck effects were only observed in snails from two sites (JC and YH). Although the hypothesis that snail control would greatly reduce the effective population size was not completely supported by our evidence, completely eradicating snails from XG site is possible. These findings will aid in the development of more practical guidelines for local snail monitoring and control.

Genetic diversity and population structure of Oncomelania hupensis in Sichuan Province, China: implications for schistosomiasis control

Schistosomiasis, caused by the infection with Schistosoma japonicum, remains a significant public health concern in China. As the sole intermediate host of S. japonicum, the breeding and spread of Oncomelania hupensis contribute significantly to the potential risk of disease occurrence and transmission. Exploring the population genetics of the snail vector is conducive to better understanding its distribution and dispersal patterns, and provides more data for future snail surveillance and control from a molecular perspective. The genetic diversity and population structure of O. hupensis in Sichuan Province were evaluated based on sequencing of mitochondrial cytochrome c oxidase subunit 1. A total of 215 snail isolates were collected from 30 counties, identifying 80 haplotypes with high nucleotide diversity (0.05871 ± 0.00160) and haplotype diversity (0.979 ± 0.003). Phylogenetic analysis and haplotype network construction identified five distinct clades. Notably, clade 1 was confined within the Panxi region, while clade 5 exhibited a widespread distribution across the studied areas, distinct from the other four clades, but showing a close genetic relationship to individuals from Yunnan. Spatial differentiation was revealed by significant pairwise genetic distance values detected in 313 out of 435 population pairs, ranging from 0.07632 to 1.00000. Analysis of molecular variance (AMOVA) showed that the majority of variance occurred among populations, but significant differences were also observed among landscape groups. AMOVA also provided support for clade separation by exhibiting significant genetic differences among the clades, which explained 78.23% of the overall variation. Geographical distance and precipitation were found to display a significant correlation with the genetic differentiation pattern of O. hupensis in both Mantel and partial Mantel tests. Temporal stability was observed over sampling intervals of 7 years, particularly among snail populations inhabiting the Panxi area, despite prolonged molluscicide treatment. This study provides updated insights into the genetic diversity and population structure of O. hupensis in Sichuan Province, which contribute to a better understanding of the challenges faced in snail control. In light of the findings, the integration of molecular insights into snail monitoring and control, and the reinforcement of collaborative efforts in neighboring regions, in addition to long-distance monitoring, are suggested.

Genetic differentiation of Oncomelania hupensis robertsoni in hilly regions of China: Using the complete mitochondrial genome

OBJECTIVE

Oncomelania hupensis robertsoni is the only intermediate host of Schistosoma japonicum in hilly regions of south-west China, which plays a key role during the transmission of Schistosomiasis. This study aimed to sequence the complete mitochondrial genome of Oncomelania hupensis robertsoni and analyze genetic differentiation of Oncomelania hupensis robertsoni.

METHODS

Samples were from 13 villages in Yunnan Province of China, with 30 Oncomelania hupensis snails per village, and the complete mitochondrial genome was sequenced. A comprehensive analysis of the genetic differentiation of Oncomelania hupensis robertsoni was conducted by constructing phylogenetic trees, calculating genetic distances, and analyzing identity.

RESULTS

A total of 26 complete mitochondrial sequences were determined. The length of genome ranged from 15,181 to 15,187 bp, and the base composition of the genome was A+T (67.5%) and G+C content (32.5%). This genome encoded 37 genes, including 13 protein-coding genes, 2 rRNA genes, and 22 tRNA genes. The phylogenetic trees and identity analysis confirmed that Oncomelania hupensis robertsoni was subdivided into Oncomelania hupensis robertsoni Yunnan strain and Sichuan strain, with a genetic distance of 0.0834. Oncomelania hupensis robertsoni Yunnan strain was further subdivided into two sub-branches, corresponding to "Yunnan North" and "Yunnan South", with a genetic distance of 0.0216, and the samples exhibited over 97% identity.

CONCLUSION

Oncomelania hupensis robertsoni is subdivided into Oncomelania hupensis robertsoni Yunnan strain and Sichuan strain. Oncomelania hupensis robertsoni Yunnan strain exhibits a higher level of genetic identity and clear north-south differentiation. This work reported the first mitochondrial genome of Oncomelania hupensis robertsoni Yunnan strain, which could be used as an important reference genome for Oncomelania hupensis, and also provide the important information for explaining the distribution pattern of Oncomelania hupensis robertsoni and control of Schistosoma japonicum.

The genetic diversity of Oncomelania hupensis robertsoni, intermediate hosts of Schistosoma japonicum in hilly regions of China, using microsatellite markers

BACKGROUND

The elimination of schistosomiasis remains a challenging task, with current measures primarily focused on the monitoring and control of Oncomelania hupensis (O. hupensis) snail, the sole intermediate host of Schistosome japonicum. Given the emerging, re-emerging, and persistent habitats of snails, understanding their genetic diversity might be essential for their successful monitoring and control. The aims of this study were to analyze the genetic diversity of Oncomelania hupensis robertsoni (O. h. robertsoni) using microsatellite DNA markers; and validate the applicability of previously identified microsatellite loci for O. hupensis in hilly regions.

METHODS

A total of 17 populations of O. h. robertsoni from Yunnan Province in China were selected for analysis of genetic diversity using six microsatellite DNA polymorphic loci (P82, P84, T4-22, T5-11, T5-13, and T6-27).

RESULTS

The number of alleles among populations ranged from 0 to 19, with an average of 5. The average ranges of expected (He) and observed (Ho) heterozygosity within populations were 0.506 to 0.761 and 0.443 to 0.792, respectively. The average fixation index within the population ranged from - 0.801 to 0.211. The average polymorphic information content (PIC) within the population ranged from 0.411 to 0.757, appearing to be polymorphic for all loci (all PIC > 0.5), except for P28 and P48. A total of 68 loci showed significant deviations from Hardy-Weinberg equilibrium (P < 0.05), and pairwise Fst values ranged from 0.051 to 0.379. The analysis of molecular variance indicated that 88% of the variation occurred within snail populations, whereas 12% occurred among snail populations. Phylogenetic trees and principal coordinate analysis revealed two distinct clusters within the snail population, corresponding to "Yunnan North" and "Yunnan South".

CONCLUSIONS

O. h. robertsoni exhibited a relatively high level of genetic differentiation, with variation chiefly existing within snail populations. All snail in this region could be separated into two clusters. The microsatellite loci P82 and P84 might not be suitable for classification studies of O. hupensis in hilly regions. These findings provided important information for the monitoring and control of snail, and for further genetic diversity studies on snail populations.