Single- or mixed-sex Schistosoma japonicum infections of intermediate host snails in hilly areas of Anhui, China

Construction and characterization of microsatellite markers for the Schistosoma japonicum isolate from a hilly area of China based on whole genome sequencing

Schistosoma japonicum had once caused the greatest disease burden in China and has still been transmitted in some hilly areas, for example, in Shitai of Anhui province, where rodents are projected to be the main reservoir. This may lead to a critical need of molecular tools with high efficiency in monitoring the dynamic of the rodent-associated S. japonicum, as an appropriate amount of schistosome input can re-establish its life cycle in a place with snails and then result in the re-emergence of schistosomiasis. Therefore, the goal of this study was to develop high polymorphic microsatellites from the whole genome of rodent-associated S. japonicum strain to monitor its transmission dynamic. We sampled the hilly schistosome isolate from Shitai of Anhui in China and sequenced the parasite with the next-generation sequencing technology. The whole genome was assembled with four different approaches. We then developed 71 microsatellite markers at a genome-wide scale throughout two best assembled genomes. Based on their chromosome mapping and the expected length of targeted sequences, we selected 24 markers for the development of multiplex reactions. Two multiplexes composed of 10 loci were finally developed, and their potential was revealed by their successful application on and capturing the genetic diversity of three schistosome populations. The selected 10 markers, each with clear chromosome location and characteristics, will be greatly useful in tracing the dispersal pathways or/and dynamics of the rodent-associated S. japonicum or others in the hilly area of China or elsewhere.

Single-sex schistosomiasis: a mini review

Schistosomiasis is a neglected tropical disease caused by dioecious blood flukes of the genus Schistosoma and second to malaria as a parasitic disease with significant socio-economic impacts. Mating is essential for maturation of male and female schistosomes and for females to lay of eggs, which are responsible for the pathogenesis and propagation of the life cycle beyond the mammalian host. Single-sex schistosomes, which do not produce viable eggs without mating, have been overlooked given the symptomatic paucity of the single-sex schistosomiasis and limited diagnostic toolkit. Besides, single-sex schistosomes are less sensitive to praziquantel. Therefore, these issues should be considered to achieve the elimination of this infection disease. The aim of this review is to summarize current progress in research of single-sex schistosomes and host-parasite interactions.

In vivo efficiency of praziquantel treatment of single-sex Schistosoma japonicum aged three months old in mice

Schistosomiasis is a major neglected tropical disease mainly caused by Schistosoma haematobium, S. japonicum and S. mansoni, and results in the greatest disease burden. Mass drug administration (MDA) with praziquantel (PZQ), a single drug only available for the disease, has played a vital role in schistosomiasis control. Therefore, any possibility of selection of the parasites for PZQ resistance or low sensitivity may hamper the 2030's target of global disease elimination. We had experimentally demonstrated the long-term survival and reproductive potential of single-sex (of either sex) S. japonicum infections in definitive hosts mice. What has not yet been adequately addressed is whether the long live single-sex schistosomes remain sensitive to PZQ, and what reproduction potential for those schistosomes surviving treatment may have. We therefore performed experimental mice studies to explore the treatment effectiveness of PZQ (at total doses of 200 or 400 mg/kg, corresponding to the sub-standard or standard treatment doses in humans) for single-sex S. japonicum aged three months old. The results showed that no treatment efficiency was observed on female schistosomes, whereas on male schistosomes only at PZQ 400 mg/kg a significant higher efficiency in reducing worm burdens was observed. Moreover, either schistosome males or females surviving PZQ treatment remained their reproduction potential as normal. The results indicate that long (i.e., three months) live single-sex S. japonicum can easily survive the current treatment strategy, and moreover, any schistosomes, if with PZQ resistance or low sensitivity, could be easily transmitted in nature. Therefore, in order to realize the target for the national and the global schistosomiasis elimination, there is undoubtedly a great need for refining PZQ administration and dosage, looking for alternative therapies, and/or developing vaccines against schistosome.

Extended survival and reproductive potential of single-sex male and female Schistosoma japonicum within definitive hosts

Schistosomiasis is caused by dioecious helminths of the genus Schistosoma. Recent work indicated that unpaired female and male schistosomes can survive within their definitive host for at least 1 year, although the viability or fertility of these worms after subsequent pairing remained untested. We performed two experiments on laboratory mice, one with female Schistosoma japonicum exposure first and male schistosomes second and another vice versa. After surviving as single-sex unpaired forms for up to 1 year, 58.5% of male and 70% of female schistosomes were able to mate and produce viable eggs. This highlights an additional biological challenge in achieving elimination of schistosomiasis.

Differential expression of microRNA between normally developed and underdeveloped female worms of Schistosoma japonicum

Eggs produced by bisexual infected mature female worms (MF) of Schistosoma japonicum are important in the transmission of the parasite and responsible for the pathogenesis of schistosomiasis. The single-sex infected female worms (SF) cannot mature and do not produce normal eggs; also they do not induce severe damage to the host. In this study, the microRNA (miRNA) expression profiles of 25d MF and 25d SF were investigated through Solexa deep-sequencing technology to explore the developmental mechanisms of schistosome female worms. There were 36 differentially expressed miRNA, 20 up-regulated and 16 down-regulated found in MF/SF worms, including some development related miRNA such as bantam (ban), let-7, miR-124, miR-8, miR-1, miR-7. There were 166 target genes of up-regulated miRNA and 201 target genes of down-regulated miRNA after comparing the target gene prediction software results with RNA-Seq transcriptome results. Analysis of the target genes shows that different ones are involved in MF and SF worms in Gene Ontology terms, with a similar situation in KEGG. This observation indicates that different genes regulated by differentially expressed miRNA take part in MF and SF and lead to differential sexual status. This means that the sexual status of female worms is regulated by miRNA.

Duplex real-time PCR for sexing Schistosoma japonicum cercariae based on W chromosome-specific genes and its applications

As a unique feature among otherwise hermaphroditic trematodes, Schistosoma species are gonochoric parasites whose sex is genetically determined (ZZ for males and ZW for females). However, schistosome larvae are morphologically identical, and sex can only be discriminated by molecular methods. Here, we integrated published Schistosoma. japonicum transcriptome and genome data to identify W chromosome-specific genes as sex biomarkers. Three W chromosome-specific genes of S. japonicum were identified as sex biomarkers from a panel of 12 genes expressed only in females. An efficient duplex real-time PCR (qPCR) method for sexing cercariae was developed which could identify the sex of cercariae within 2 h without DNA extraction. Moreover, this method can be used to identify not only single-sex but also mixed-sex schistosome-infected snails. We observed a nearly equal proportion of single-male, single-female, and mixed-sex schistosome infections in artificially infected snails. Sex-known schistosome-infected snail models can be efficiently constructed with the aid of duplex qPCR. A field study revealed that single-sex schistosome infections were predominant among naturally infected snails. Finally, a schistosomiasis mouse model based on sex-known cercariae infection was shown to be more reliable than a model based on sex-unknown cercariae infection. The developed duplex qPCR method for sexing S. japonicum cercariae can be widely used for schistosomiasis modeling, genetic experiments, and field-based molecular epidemiological studies.

Schistosoma japonicum is a major causative agent of human schistosomiasis. Unlike other parasitic worms, S. japonicum females are determined by the heterogametic sex chromosome (ZW) and males by the homogametic sex chromosome (ZZ). The life cycle of S. japonicum includes the egg, miracidium, mother sporocyst, daughter sporocyst, cercaria, schistosomulum, and adult stages. The sex of adult male and female worms can be morphologically distinguished, whereas the sex of larvae, such as cercariae, can only be discriminated by molecular methods. In this study, we established an efficient duplex real-time PCR method for sexing S. japonicum cercariae based on newly identified W chromosome-specific genes. The established duplex real-time PCR method will facilitate construction of sex-controlled schistosome-infected intermediate host or definitive host models for schistosome-host interplays and schistosomiasis studies. This method is also a powerful tool for investigating the epidemiology of single-sex and mixed-sex schistosome-infected snails in the field.

Population genetics of Oncomelania hupensis snails, intermediate hosts of Schistosoma japonium, from emerging, re-emerging or established habitats within China

Schistosomiasis remains one of the world's most significant neglected tropical diseases, second only to malaria in terms of socioeconomic impact. In 2014, China proposed the goal of schistosomiasis japonicum elimination by 2025. However, one major challenge is the widely distributed, and in certain cases potentially increasing, habitats of Oncomelania hupensis, the snail intermediate hosts of S. japonicum. Therefore, an understanding of population genetics of O. hupensis in new or re-emerged habitats, together with that of the established habitats with snail persistence, would be valuable in controlling and predicting the future transmission dynamics of schistosomiasis in China. Using nine microsatellite loci, we conducted population genetic analyses of snails sampled from one habitat where snails were detected for the first time, one (previously eliminated) habitat with re-emerged snails, and one habitat with established snail persistence. Results showed lower diversities, in terms of number of observed alleles per locus (Na), number of effective alleles per locus (NeA), observed (Ho) and expected heterozygosity (He), in snails from new or re-emerged snail habitats than from the habitat with snail persistence. The smallest effective population size was inferred in the re-emerged snail habitat, but the largest was in the new habitat rather than in the habitat with snail persistence. No bottleneck effects were detected in new or re-merged habitats. No or low sub-structure was inferred in new and persistent snail habitats. Snails from the three sites were clearly separated and low gene flow was estimated between sites. We propose that snails at the new habitat may have been introduced through immigration, whereas snails at the re-emerged habitat may be the consequence of those few snails remaining subsequently expanding through reproduction. We discuss our results in terms of their theoretical and applied implications.

Characterization and expression analysis of Wnt5 in Schistosoma japonicum at different developmental stages

Wnt signaling is a key pathway involving the regulation of cell development and growth in metazoa. An analysis of Wnt signaling in Schistosoma japonicum might provide information regarding the molecular mechanisms underlying parasite development, which might be useful for vaccine screening and identification of pharmaceutical targets. The SjWnt5 gene, a member of the Wnt gene family, contained an 1149-bp open reading frame that encoded a 382-aa protein. Analysis of the SjWnt5 amino acid sequence revealed a domain that was conserved among members of the Wnt protein family. Expression of SjWnt5 was observed at all of the developmental stages in definitive hosts, and the highest level of SjWnt5 messenger RNA (mRNA) was detected at the schistosomula stage. Higher levels of SjWnt5 mRNA and protein were observed in mature male worms, compared with those in mature females. SjWnt5 mRNA was expressed at higher levels in maldeveloped worms from nonpermissive host or single-sex infection than in normal worms from permissive host and mixed-sex infection. The immunohistochemical analysis showed that SjWnt5 protein was expressed in the subtegumental musculature and acetabulum musculature of schistosomulum and adult worms, suggesting that SjWnt5 may play a role in regulation of parasite muscle development. Furthermore, SjWnt5 was found prominently expressed in the testes of the male and the ovary as well as the vitellarium of the female, suggesting that SjWnt5 may involve in the development of the reproductive organs of both sexes.