Bayesian estimation of community prevalences of Schistosoma japonicum infection in China

A Bayesian approach to overcome the imperfections of an immunological test (an antibody-based ELISA) and a parasitological test (Kato-Katz) in the detection of Schistosoma japonicum infection, was used to estimate community prevalences of S. japonicum infection in China. At the same time, the similarity between the prevalence estimates based on data from ELISA alone and those using data from both ELISA and Kato-Katz tests was explored. The database from the third nationwide sampling survey of schistosomiasis in China, 2004, was used for analysis, in which a total of 239 endemic villages were sampled from seven endemic provinces through a stratified cluster sampling technique and 250,987 residents aged from 6 to 65 years, were examined by ELISA followed by a Kato-Katz test applied to the seropositives. Bayesian hierarchical models incorporating random effects to reflect the nested data structure and uncertainty about test properties were employed to analyse the data. Our analysis suggested that using data from ELISA alone or both ELISA and Kato-Katz tests resulted in similar prevalence estimates, probably owing to the lack of sensitivity of Kato-Katz and the fact that Kato-Katz was only applied to the seropositives. We conclude that it is feasible to employ only ELISA, instead of combined ELISA and Kato-Katz tests, to estimate prevalence of S. japonicum infection in large-scale epidemiological settings. This study confirmed heterogeneity in the prevalence of S. japonicum infection in space by the fact that the estimated prevalences of S. japonicum infection in the sampled villages ranged from 0.02% to about 56% (posterior median). It is indicated that the disease remains a threat in some areas along the Yangtze River, although great achievements have been made in the control programme of schistosomiasis in China.     

Schistosoma japonicum: treatment of different developmental stages in mice with long-acting praziquantel implants

This paper reports the effective treatment of Schistosoma japonicum in a mouse model with long-acting praziquantel (PZQ)-loaded poly(ε-caprolactone) implants. The implants yielded stable, high plasma PZQ concentrations ranging 100–1600 ng/mL during the 40-day investigation period. For assessment of efficacy, the implants were implanted into mice immediately after infection and at 1, 2, 3 and 4 weeks after infection to treat the schistosomes at different developmental stages. All the mice were sacrificed at 6 weeks after infection for worm and egg recovery, worm morphology examination, and histopathological analysis of implantation site tissues. The worm burdens, egg burdens, and numbers of miracidia hatched from the retrieved eggs for all the implant-treated groups (except groups T2-A, T4 and T5) were reduced by 100% when compared with the control group. From groups T2-A, T4 and T5, some schistosome debris was recovered. Eggs were found in only group T5 for which the time between infection and implantation was 4 weeks, which enabled the maturation of juvenile female schistosomes into adult ones that lay eggs. Histopathological observations of implantation tissue showed no evidence of granulomatous foreign-body or lymphoid cell aggregation, demonstrating good biocompatibility of the PZQ implants. These results demonstrate that the long-acting PZQ implants can kill schistosomes at any developmental stages and attenuate/avoid the associated liver damage.     

Familial aggregation of human infection with Schistosoma japonicum in the Poyang Lake region, China

Despite the success of extensive control measures that have been implemented in China for over 50 years, the number of individuals infected with Schistosoma japonicum remains high in the existing endemic areas. A variance components analysis was undertaken to estimate the heritable and environmental components that contribute to S. japonicum infection in the Poyang Lake region of Jiangxi Province, PR China. The total target population was 3148 from four separate administrative villages. Two thousand seven hundred and five of these comprised 400 families ranging in size from 3 to 188. After adjustments were made for gender, water contact and past history of having had schistosomiasis, the heritable component was estimated to account for as much as 58% of the phenotype variation under the polygenic model. Household was not shown to be an important environmental factor. Incorporating village effects indicated that the results were valid for the total population. We conclude that genetic heritability in this region is high and plays an important role in determining risk of infection with S. japonicum.     

Vaccine potential of hemocyanin from Oncomelania hupensis against Schistosoma japonicum

Hemocyanin, a giant oxygen transport protein which is usually found in many arthropods and mollusks was isolated and purified from Oncomelania hupensis. In this study, we showed that Oncomelania hupensis hemocyanin (OhH) shared carbohydrate epitopes with different developmental stages of Schistosoma japonicum (Cercaria, Schistosomulum, Adult worm and Egg) and exhibited serological cross-reaction with these stages of S. japonicum immune sera, which had a potential for use in diagnostic and therapeutic studies of schistosomasis. OhH was used as a vaccine in combination with Freund's adjuvant to evaluate the induction of immune responses and protection against S. japonicum infection in mice. Mice immunized with OhH induced a Th1 type of immune responses. Strong protection against S. japonicum were observed in adult worm and egg burdens after 42 days post-challenge, which showed a significant worm reduction of 52.5% and egg reduction of 69.2% compared to the control groups, respectively. These results indicated that OhH was a potential candidate to compose an anti-schistosome vaccine.     

Schistosoma mekongi: a prominent neutrophil chemotactic activity of egg antigen with reference to that of Schistosoma japonicum

Schistosoma mekongi causes granulomatous lesions around eggs deposited in the liver with neutrophil-rich inflammatory reactions in the early stage of the egg laying. To define the aspects of the typical pathogenesis of S. mekongi infection, we determined the difference between soluble egg antigen (SEA) from S. mekongi and S. japonicum with a focus on chemotactic factors for neutrophils or eosinophils. Mean volume and protein amount of S. mekongi eggs was 71 and 58% of those of Schistosoma japonicum eggs, respectively. Neutrophil chemotactic activity of S. mekongi SEA was about two times higher than that of S. japonicum. In contrast, eosinophil chemotactic activity of S. mekongi SEA was about half of that of S. japonicum SEA. Molecular analysis revealed that S. mekongi SEA contains higher molecular-weight components with a lower level of glycosylation, and this is likely to be related to the intense neutrophil chemotactic activity in comparison with S. japonicum SEA. The prominent chemotactic reactivity for neutrophils is likely to be involved in the typical pathogenesis of mekongi schistosomiasis.     

Schistosoma japonicum: The design and experimental evaluation of a multivalent DNA vaccine

The aim of this study was to construct and evaluate the immunity efficacy of the DNA multivalent vaccine pVIVO₂SjFABP-23. The vaccine was constructed and produced as follows. Forty BALB/c mice were divided into four groups designated pVIVO₂, pVIVO₂Sj23, pVIVO₂SjFABP and pVIVO₂SjFABP-23. Each mouse was immunized with 100 μg of the corresponding plasmid DNA by intramuscular injection. 28 days post-vaccination, the mice were challenged with S. japonicum cercariae, and the worm and egg burdens were determined 42 days post-challenge. Serum samples were collected from all the mice before and after vaccination and at the end of the experiment, and used for antibody detection. The IFN-γ and IL-4 levels were quantified in the supernatants of specifically stimulated spleen cells. The number of worms was reduced by 52%, 40% and 42% in mice respectively immunized with pVIVO₂SjFABP-23, pVIVO₂Sj23 or pVIVO₂SjFABP. A respective 61%, 38% and 39% egg reduction was determined relative to those mice that only received the empty pVIVO2 plasmid. pVIVO₂SjFABP-23 immunization increased IgG levels against SWAP and SEA. Increased IFN-γ levels were detected in the supernatant of specific stimulated spleen cells from mice immunized with the 3 different constructs. The multivalent DNA vaccine developed induced higher levels of protection than the two monovalent tested vaccines.     

Reconstruction and in silico analysis of the MAPK signaling pathways in the human blood fluke, Schistosoma japonicum

At present, little is known about signal transduction mechanisms in schistosomes, which cause the disease of schistosomiasis. The mitogen-activated protein kinase (MAPK) signaling pathways, which are evolutionarily conserved from yeast to Homo sapiens, play key roles in multiple cellular processes. Here, we reconstructed the hypothetical MAPK signaling pathways in Schistosoma japonicum and compared the schistosome pathways with those of model eukaryote species. We identified 60 homologous components in the S. japonciumMAPK signaling pathways. Among these, 27 were predicted to be full-length sequences. Phylogenetic analysis of these proteins confirmed the evolutionary conservation of the MAPK signaling pathways. Remarkably, we identified S. japonicum homologues of GTP-binding protein beta and alpha-I subunits in the yeast mating pathway, which might be involved in the regulation of different life stages and female sexual maturation processes as well in schistosomes. In addition, several pathway member genes, including ERK, JNK, Sja-DSP, MRAS and RAS, were determined through quantitative PCR analysis to be expressed in a stage-specific manner, with ERK, JNK and their inhibitor Sja-DSP markedly upregulated in adult female schistosomes.     

A Bayesian-based approach for spatio-temporal modeling of county level prevalence of Schistosoma japonicum infection in Jiangsu province, China

Spatio-temporal variations of Schistosoma japonicum infection risk in Jiangsu province, China, were examined and the relationships between key climatic factors and infection prevalence at the county level were determined. The parasitological data were collected annually by means of cross-sectional surveys carried out in 47 counties from 1990 to 1998. Climatic factors, namely land surface temperature (LST) and normalized difference vegetation index (NDVI), were obtained from remote sensing satellite sensors. Bayesian spatio-temporal models were employed to analyze the data. The best fitting model showed that spatial autocorrelation in Jiangsu province decreased dramatically from 1990 to 1992 and increased gradually thereafter. A likely explanation of this finding arises from the large-scale administration of praziquantel for morbidity control of schistosomiasis. Our analysis suggested a negative association between NDVI and risk of S. japonicum infection. On the other hand, an increase in LST contributed to a significant increase in S. japonicum infection prevalence. We conclude that combining geographic information system, remote sensing and Bayesian-based statistical approaches facilitate integrated risk modeling of S. japonicum, which in turn is of relevance for allocation of scarce resources for control of schistosomiasis japonica in Jiangsu province and elsewhere in China, where the disease remains of public health and economic significance.     

Adverse effects of praziquantel treatment of Schistosoma japonicum infection: involvement of host anaphylactic reactions induced by parasite antigen release

The present study using a murine model heavily infected with Schistosoma japonicum aimed to elucidate the pathogenesis of adverse effects of praziquantel treatment of schistosome-infected subjects. Inbred BALB/c mice were infected with S. japonicum (Yamanashi strain) before being treated with a single dose of praziquantel at 4 or 8 weeks p.i. All the mice treated at 8 weeks p.i. exhibited signs typical of systemic anaphylaxis until half of them died shortly after praziquantel administration. At autopsy, these mice exhibited remarkable intestinal alterations characterised by increased mucosal permeability, mucosal oedema and petechial haemorrhage, which are changes typical of immediate intestinal anaphylaxis. In these mice treated at 8 weeks p.i., degranulation of intestinal mast cells was frequently observed, which was particularly remarkable around S. japonicum eggs hatched as an effect of praziquantel. Furthermore, the plasma histamine concentration just after praziquantel treatment was much higher in mice at 8 weeks p.i. than that in uninfected mice or in S. japonicum-infected mice without drug treatment. In contrast, none of these intestinal changes was observed in untreated or uninfected control mice, or in mice administered praziquantel at 4 weeks p.i., in which worm pairs had just reached sexual maturation and begun egg-laying. The finding by ELISA that serum IgM and IgA levels specific to S. japonicum eggs decreased immediately after praziquantel treatment, together with the results of immunohistochemistry, revealed the sudden release of parasite antigens from the eggs hatched by praziquantel treatment. The results of this study demonstrate that adverse effects of praziquantel treatment of schistosomiasis characterised by abdominal signs depend on anaphylactic reactions due to parasite antigens, especially antigens from eggs hatched as an effect of praziquantel.     

Molecular Differentiation of Schistosoma japonicum and Schistosoma mekongi by Real-Time PCR with High Resolution Melting Analysis

Human schistosomiasis caused by Schistosoma japonicum and Schistosoma mekongi is a chronic and debilitating helminthic disease still prevalent in several countries of Asia. Due to morphological similarities of cercariae and eggs of these 2 species, microscopic differentiation is difficult. High resolution melting (HRM) real-time PCR is developed as an alternative tool for the detection and differentiation of these 2 species. A primer pair was designed for targeting the 18S ribosomal RNA gene to generate PCR products of 156 base pairs for both species. The melting points of S. japonicum and S. mekongi PCR products were 84.5±0.07℃ and 85.7±0.07℃, respectively. The method permits amplification from a single cercaria or an egg. The HRM real-time PCR is a rapid and simple tool for differentiation of S. japonicum and S. mekongi in the intermediate and final hosts.     

Cimetidine enhances the protective effect of GST DNA vaccine against Schistosoma japonicum

Cimetidine (CIM), a histamine-2-receptor antagonist, has a long history of safe use in gastric acid-mediated gastrointestinal disorders. In this study, we used CIM, as an adjuvant, with pEGFP-Sj26 GST (the recombinant plasmid containing enhanced green fluorescent protein gene and the gene encoding 26 kDa glutathione S-transferase of Schistosoma japonicum) DNA vaccine to immunized mice and attempted to enhance the protective effect against S. japonicum. The results showed that the reduction rate of worm and egg burdens in the pEGFP-Sj26GST plus CIM group were 79.0% and 68.4%, respectively, significantly higher than that in pEGFP-Sj26GST alone group (27.0% and 22.5%, P < 0.01). Compared with the pEGFP-Sj26GST alone group, mice immunized with pEGFP-Sj26GST plus CIM showed an elevated level of IFN-γ and IL-12 and a low level of IL-10 in splenocytes, while the levels of IL-4 and IL-5 showed no difference between the two groups. Our data also demonstrated that the percentage of CD4⁺CD25⁺ regulatory T cells (Tregs) was significantly decreased in the spleens of mice immunized with pEGFP-Sj26GST plus CIM. All these findings suggest that CIM as a potential schistosome DNA vaccine adjuvant can enhance the protective effect of pEGFP-Sj26GST vaccine.     

Thin layer chromatographic analysis of glucose and maltose in estivated Biomphalaria glabrata snails and those infected with Schistosoma mansoni

Thin layer chromatography was used to analyze the glucose and maltose concentrations of the digestive gland–gonad complex (DGG) of uninfected-estivated Biomphalaria glabrata snails and estivated B. glabrata patently infected with Schistosoma mansoni. All snails were estivated in a most chamber at a relative humidity of 98 ± 1% and a temperature of 23 ± 1 °C for 14 days. Carbohydrates were extracted from the DGG with 70% aqueous ethanol, and extracts were analyzed on silica gel preadsorbent plates using ethyl acetate–glacial acetic acid–methanol–water (60:15:15:10) mobile phase, α-naphthol–sulfuric acid detection reagent, and quantification by densitometry. The concentrations of glucose and maltose were significantly reduced in both uninfected-estivated snails and infected-estivated snails.     

Identification of in vivo protein phosphorylation sites in human pathogen Schistosoma japonicum by a phosphoproteomic approach

Schistosome is the causative agent of human schistosomiasis and related animal disease. Reversible protein phosphorylation plays a key role in signaling processing that are vital for a cell and organism. However, it remains to be undercharacterized in schistosomes. In the present study, we characterized in vivo protein phosphorylation events in different developmental stages (schistosomula and adult worms) of Schistosoma japonicum by using microvolume immobilized metal-ion affinity chromatography (IMAC) pipette tips coupled to nanoLC-ESI-MS/MS. In total, 127 distinct phosphorylation sites were identified in 92 proteins in S. japonicum. A comparison of the phosphopeptides identified between the schistosomula and the adult worms revealed 30 phosphoproteins co-detected in both of the two worms. These proteins included several signal molecules and enzymes such as 14-3-3 protein, cysteine string protein, heat shock protein 90, epidermal growth factor receptor pathway substrate 8, proliferation-associated protein 2G4, peptidyl-prolyl isomerase G, phosphofructokinase and thymidylate kinase. Additionally, the phosphorylation sites were examined for phosphorylation specific motif and evolutionarily conservation. The study represents the first attempt to determine in vivo protein phosphorylation in S. japonicum by using a phosphoproteomic approach. The results by providing an inventory of phosphorylated proteins may facilitate to further understand the mechanisms involved in schistosome development and growth, and then may result in the development of novel vaccine candidates and drug targets for schistosomiasis control.     

Energy allocation patterns in Biomphalaria alexandrina snails in response to cadmium exposure and Schistosoma mansoni infection

This study was aimed to investigate the effects of both parasitism and environmental stress on the growth, reproduction, and survival of Biomphalaria alexandrina snails. Resource allocation strategies may be influenced by both biotic and abiotic factors. Using the planorbid snail B. alexandrina and Schistosoma mansoni, this hypothesis was examined by raising snails fed the same diet under two stressors (infection and Cd exposure). The snails divided into four groups, uninfected, infected, Cd-exposed uninfected, and Cd-exposed infected snails. Egg production, growth, and survival of the snails were monitored over a 9-week period postinfection. Inhibition of snail reproductive activity by parasitism results in increased snail growth in the first week postinfection, termed gigantism, during which the snail is hypothesized to allocate excess energy normally used for reproduction to somatic growth. Infection status and Cd exposure had significant effects on snail growth and reproduction. The infected and Cd-exposed infected snails exhibiting reduced survival relative to snails of other treatments. It was found that parasite development influenced by Cd exposure. Results of this study suggest that energy allocation patterns are context-dependent in B. alexandrina snails, influenced by infection and Cd exposure.     

Possible implications of CpG avoidance in the flatworm Schistosoma mansoni

We report the analysis of the biases of CpG, TpG, and CpA of all the DNA sequences data from the Trematode Schistosoma mansoni. Our results show CpG avoidance whereas TpG and CpA frequencies are over the expected values. These characteristics are similar to the biases displayed by methylated genomes, but in platyhelminths 5mC has not been detected by biochemical methods. The possible implications of this CpG shortage are discussed.