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Species and subspecies of the Oncomelania hupensis species complex are recognized as intermediate hosts of Schistosoma japonicum. Of these species and subspecies, O. quadrasi is distributed throughout the Philippines. This study used 12S ribosomal RNA sequences to explore the genetic structure of O. quadrasi populations in the Philippines. Three su...
Citations
... h. hupensis) is the only intermediate hosts of Schistosoma japonicum, the major causative agent of schistosomiasis in countries in Southeast Asia [1]. China once profoundly suffered from schistosomiasis [2]. ...
... The average genetic divergence between any two populations was observed as significantly large [36], indicating lack or low level of gene flow between them. This may be also potentially related to the low mobility of the snail species, leading to population subdivision and potential increase in global genetic diversity [1]. The only exception was between HX and ZY in Anhui, either of which is located along the lower reaches of the Yangtze River. ...
Background
Oncomelania hupensis hupensis is the only intermediate host of Schistosoma japonicum, the causative agent of schistosomiasis in China and is therefore of significant medical and veterinary health importance. Although tremendous progress has been achieved, there remains an understudied area of approximately 2.06 billion m2 of potential snail habitats. This area could be further increased by annual flooding. Therefore, an understanding of population genetics of snails in these areas may be useful for future monitoring and control activities.Methods and resultsWe sampled snails from Hexian (HX), Zongyang (ZY) and Shitai (ST) in Anhui (schistosomiasis transmission control), and from Hengtang (HT), Taicang (TC), Dongsan (DS) and Xisan (XS) in Jiangsu (schistosomiasis transmission interrupted), downstream of Anhui. ST, DS and XS are classified as hilly and mountainous areas, and HX, ZY, TC and HT as lake and marshland areas. The mitochondrial cytochrome c oxidase subunit I gene were sequenced. Out of 115 snails analyzed, 29 haplotypes were identified. We observed 56 (8.72%) polymorphic sites consisting of 51 transitions, four transversions and one multiple mutational change. The overall haplotype and nucleotide diversity were 0.899 and 0.01569, respectively. Snail populations in Anhui had higher genetic diversity than in Jiangsu. 73.32% of total variation was distributed among sites and 26.68% within sites. Snails were significantly separated according to eco-epidemiological settings in both network and phylogenetic analyses.Conclusion
Our results could provide important guidance towards assessing coevolutionary interactions of snails with S. japonicum, as well as for future molluscan host monitoring and control activities.
... Hope and McManus (1994) used polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) to directly examine the internal transcribed spacer (ITS) gene, and found minor variation among Philippine snails. A recent paper of Saijuntha et al. (2014) Occidental were included in the analysis. The 16S rRNA gene was selected since previous studies have demonstrated its utility to assess genetic variation in populations in the aquatic snail Potamopyrgus antipodorum (Stadler et al. 2005), the slug Arion subfucus (Pinceel et al. 2005), the giant African snail Achatina fulica (Fontanilla et al. 2014), and the pomatiopsid snail Neotricula aperta (Attwood et al. 2008). ...
... The lack of genetic substructuring among the O. h. quadrasi isolates based on the 16S gene in this study is in contrast to what Saijuntha et al. (2014) observed. Combining the markers may provide greater phylogenetic signal and more variable positions. ...
Schistosomiasis japonica is a water-borne trematode infection transmitted by different subspecies of Oncomelania hupensis. As parasites may either co-evolve or locally adapt with their hosts, snail diversity, as revealed by morphometric and genetic studies, may reflect parasite diversity and elucidate snail susceptibility and transmission patterns. This study aimed to compare isolates of O. h. quadrasi based on a 342-bp fragment of the 16S ribosomal RNA gene. O. h. quadrasi isolates were collected from nine provinces known to have S. japonicum in the Philippines, namely Cagayan Valley, Bohol, Negros Occidental, Leyte, Davao, Davao del Sur, Mindoro Oriental, Northern Samar, and Sorsogon. O. h. hupensis and O. h. nosophora isolates were also collected from China and Japan, respectively. The 16S ribosomal RNA gene of each specimen was amplified and sequenced. Phylogenetic and network analyses based on the 221 16S rRNA gene sequences revealed that O. h. quadrasi clustered as a distinct clade from the two other subspecies. Of the four identified haplotypes for O. h. quadrasi, two haplotypes were from Negros Oriental (Ohq2 and Ohq3), and one haplotype was from Bohol (Ohq4). The isolates from the remaining seven provinces shared a common haplotype (Ohq1). The current study was able to show the relationship among O. hupensis subspecies and demonstrate the limited ability of mitochondrial 16S ribosomal molecular marker in differentiating O. h. quadrasi geographic strains in the Philippines.
... However, previous studies on mitochondrial DNA had provided some insights into the genetic variation of the snail population of S. japonicum, and suggested that examination of naturally infected snails may exhibit co-evolutionary relationships with their parasites [32]. Thus, a snail population may reflect the population genetic parameters of their parasites [33,34]. Nevertheless, it is worth mentioning that these previous studies on the genetic diversity of Oncomelania populations are based on mitochondrial markers. ...
Background:
Microsatellites have been found to be useful in determining genetic diversities of various medically-important parasites which can be used as basis for an effective disease management and control program. In Asia and Africa, the identification of different geographical strains of Schistosoma japonicum, S. haematobium and S. mansoni as determined through microsatellites could pave the way for a better understanding of the transmission epidemiology of the parasite. Thus, the present study aims to apply microsatellite markers in analyzing the populations of S. japonicum from different endemic areas in the Philippines for possible strain differentiation.
Methodology/ principal findings:
Experimental mice were infected using the cercariae of S. japonicum collected from infected Oncomelania hupensis quadrasi snails in seven endemic municipalities. Adult worms were harvested from infected mice after 45 days of infection and their DNA analyzed against ten previously characterized microsatellite loci. High genetic diversity was observed in areas with high endemicity. The degree of genetic differentiation of the parasite population between endemic areas varies. Geographical separation was considered as one of the factors accounting for the observed difference between populations. Two subgroups have been observed in one of the study sites, suggesting that co-infection with several genotypes of the parasite might be present in the population. Clustering analysis showed no particular spatial structuring between parasite populations from different endemic areas. This result could possibly suggest varying degrees of effects of the ongoing control programs and the existing gene flow in the populations, which might be attributed to migration and active movement of infected hosts from one endemic area to another.
Conclusions/ significance:
Based on the results of the study, it is reasonable to conclude that genetic diversity could be one possible criterion to assess the infection status in highly endemic areas. Genetic surveillance using microsatellites is therefore important to predict the ongoing gene flow and degree of genetic diversity, which indirectly reflects the success of the control program in schistosomiasis-endemic areas.
... While only speculation at this stage, adaptations to new hosts, and especially to a different subspecies of snail host, may have left the signature of selection in the population. Subspecies of Oncomelania hupensis have substantial genetic and morphological differences among different endemic areas of schistosomiasis japonica [51][52][53]. Therefore, substantial genetic change might accompany a geographical and host shift. ...
Background
The blood fluke, Schistosoma japonicum still causes severe disease in China, the Philippines and Indonesia. Although there have been some studies the molecular epidemiology of this persistent and harmful parasite, few have explored the possibility and implications of selection in S. japonicum populations. Methods
We analyzed diversity and looked for evidence of selection at three nuclear genes (SjIpp2, SjFabp and SjT22.6) in 13 S. japonicum populations. ResultsSjT22.6 was found to exhibit high nucleotide diversity and was under positive selection in the mountainous region of mainland China. As a tegumental protein, its secondary and tertiary structure differed between S. japonicum strains from the mountainous and lakes regions. In contrast, SjIpp2 and SjFabp had relatively low levels of nucleotide diversity and did not show significant departure from neutrality. Conclusions
As a tegument-associated antigen-encoding gene of S. japonicum, SjT22.6 has high nucleotide diversity and appears to be under positive selection in the mountainous region of mainland China.
... As there are different subspecies of O. hupensis distributed in different endemic areas for schistosomiasis japonica e.g. 28,29,30 , and there are differences in compatibility between the snails and worms from different geographical locations 31 , we consider this separation of subspecies might not only have been an important reason for the survival of S. japonicum in new locations, but also led to the divergence of different geographically separated parasite populations. ...
The global spread of human infectious diseases is of considerable public health and biomedical interest. Little is known about the relationship between the distribution of ancient parasites and that of their human hosts. Schistosoma japonicum is one of the three major species of schistosome blood flukes causing the disease of schistosomiasis in humans. The parasite is prevalent in East and Southeast Asia, including the People’s Republic of China, the Philippines and Indonesia. We studied the co-expansion of S. japonicum and its human definitive host. Phylogenetic reconstruction based on complete mitochondrial genome sequences showed that S. japonicum radiated from the middle and lower reaches of the Yangtze River to the mountainous areas of China, Japan and Southeast Asia. In addition, the parasite experienced two population expansions during the Neolithic agriculture era, coinciding with human migration and population growth. The data indicate that the advent of rice planting likely played a key role in the spread of schistosomiasis in Asia. Moreover, the presence of different subspecies of Oncomelania hupensis intermediate host snails in different localities in Asia allowed S. japonicum to survive in new rice-planting areas, and concurrently drove the intraspecies divergence of the parasite.
... Genetic divergence observed among regional Chinese and Asian populations in this study may relate to the distribution and morphs of Oncomelania hupensis, the only intermediate host species complex involved in the transmission of S. japonicum [31]. In mainland China, there exist two distinct morphological and allozyme forms of O. hupensis: one with a smooth shell in the mountain region and another with a ribbed shell in the lake region [32,33] [34]. Oncomelania hupensis from China is genetically different from O. h. ...
... Linear regression of genetic differentiation (F ST ) based on ten microsatellite loci versus geographical distance between S. japonicum populations. [34]. These different phenotypic and genotypic morphs of O. hupensis that exist in different regions might contribute to the genetic divergences apparent among populations of its parasite, S. japonicum [35]. ...
Schistosoma japonicum is a significant public health risk in parts of China and elsewhere in Southeast Asia. To gain an insight into the epidemiology of schistosomiasis japonica, a detailed investigation of S. japonicum genetic population structure is needed.
Using three mitochondrial DNA fragments and ten microsatellite loci, we investigated the genetic diversity within and structure among twelve populations of S. japonicum sampled on a geographical scale covering most major endemic areas.
Schistosoma japonicum lineages from Indonesia, the Philippines and Chinese Taiwan were clearly distinct from each other and from those in mainland China. Within mainland China, there was some evidence for genetic divergence between populations from the mountain and lake regions. However, the analysis inferred no clear sub-population structure in the lake region of mainland China. High genetic diversity was found among S. japonicum populations of mainland China and this was significantly higher than those from island regions.
High genetic diversity within and substantial differentiation among populations were demonstrated in S. japonicum.
... The intermediate host of S. japonicum is a small operculated, amphibious and dioecious freshwater snails Oncomelania quadrasi (Pesigan et al., 1958). Very recently, Saijuntha et al. (2014) reported that Philippine O. quadrasi is genetically distinct from other Oncomelania species in Asia. Females tend to be larger than males, and eggs are laid singly on solid objects mostly above the water line (Pesigan et al., 1958). ...
A survey of Oncomelania quadrasi was conducted from December 2012 to February 2013 in the Municipalities of Kapatagan and Lala, Province of Lanao del Norte, Philippines to geo-reference location of snail colony sites, estimate snail population density and its environmental determinants, and determine the prevalence S. japonicum-infected snails. Out of 29 total villages surveyed, 25 (86.21%) were positive of infected snails. 104 (58%) of 180 water body sites (canals, streams, springs, swampy areas and wet grasslands) inspected had O. quadrasi snail colonies. Population density averages 9.9 ± 8.1SD to 11.7 ± 6.9SDmsnails per colony. Multivariate canonical correspondence analysis revealed that a combination of large habitat size of 1000-3000 sq km (p < 0.002), 0-11 cm water depth (p < 0.002) and 30.7-32.8 oC water temperature (p < 0.006) significantly explained high density of O. quadrasi populations. The mean prevalence of infected snails was 1.4 ± 0.8SD and 1.1 ± 0.3SD per colony in Kapatagan and Lala, respectively. The prevalence of S. japonicum infection in O. quadrasi is low but indicates active transmission. The geographic position of the irrigation system seems to promote the spread of O. quadrasi in the vast network of water bodies. Hence, multi-factorial and intensive control measures are necessary to
prevent transmission of schistosoma infection.
... The intermediate host of S. japonicum, Oncomelania quadrasi, has been recognized as a subspecies of O. hupensis; however, genetic evidence now indicates that O. quadrasi is a different species (Okamoto et al., 2003;Woodruff et al., 1998). The most recent investigation of the genetic structure of Oncomelania snails revealed that O. quadrasi was genetically distinct from O. hupensis at 13 mutation points, whereas the differences between subspecies of O. hupensis varied from 1 to 6 mutation points (Saijuntha et al., 2014). On the basis of the large genetic and morphological differences, O. hupensis in some sympatric areas of China has been classified as a different subspecies, i.e. ...
... O. robertsoni (Hauswald et al., 2011). These two subspecies differ from each other at 10 mutation points (Saijuntha et al., 2014). The present study showed similar evidence; the b-race N. aperta and N. aperta-like snails were highly distinct genetically from the aand g-race N. aperta at no less than 17 mutation points. ...
... The present study showed similar evidence; the b-race N. aperta and N. aperta-like snails were highly distinct genetically from the aand g-race N. aperta at no less than 17 mutation points. This finding presented further evidence, on the basis of previous evidence for Oncomelania snails (Saijuntha et al., 2014), that they constitute a different species of N. aperta than that examined in this study. Race or subspecies validity and the assignment of N. aperta in the endemic areas of lower Mekong River basin remain controversial. ...
Abstract Fifty-six samples of Neotricula aperta-like snails were collected from six locations in Cambodia. Their mitochondrial cytochrome c oxidase subunit 1 (cox1) sequences were examined using haplotype network and neighbor-joining (NJ) tree analysis. Twenty-seven haplotypes (H1-H27) were observed and were divided into two different groups/lineages. Of 27, 17 haplotypes (H11-H27) were clustered with the reference samples of the γ-race N. aperta. The remaining 10 haplotypes (H1-H10) were clustered in a separate group/lineage, differing from the reference samples of the α-, β-, and γ-race N. aperta, suggesting a new lineage belonging the genus Neotricula. Our results show that both the γ-race and a new lineage were sympatrically present approximately 60 km upstream of the Mekong River near the Kratie port, Cambodia. Further morphological and molecular studies are required to confirm the taxonomic status of this new, unidentified lineage.
