A Parallel Comparison of Antigen Candidates for Development of an Optimized Serological Diagnosis of Schistosomiasis Japonica in the Philippines

Development of a Gaussia luciferase immunoprecipitation assay for detecting Schistosoma japonicum infection

Timely and accurate diagnosis of Schistosoma infection is important to adopt effective strategies for schistosomiasis control. Previously, we demonstrated that Schistosoma japonicum can secret extracellular vesicles and their cargos may serve as a novel type of biomarkers for diagnosing schistosomiasis. Here, we developed a Gaussia luciferase immunoprecipitation assay combined with S. japonicum extracellular vesicle (SjEV) protein to evaluate its potential for diagnosing schistosomiasis. A saposin-like protein (SjSLP) identified from SjEVs was fused to the Gaussia luciferase as the diagnostic antigen. The developed method showed good capability for detecting S. japonicum infection in mice and human patients. We also observed that the method could detect Schistosoma infection in mice as early as 7 days of post-infection, which showed better sensitivity than that of indirect ELISA method. Overall, the developed method showed a good potential for detecting Schistosoma infection particularly for early stage, which may provide an alternative strategy for identify Schistosoma infection for disease control.

Comparative assessment of the SjSAP4-incorporated gold immunochromatographic assay for the diagnosis of human schistosomiasis japonica

Background

Schistosomiasis, a disease caused by parasites of the genus Schistosoma, remains a global public health threat. This study aimed to validate the diagnostic performance of a recently developed gold immunochromatographic assay (GICA) for the detection of S. japonicum infection in a rural endemic area of the Philippines.

Methods

Human clinical samples were collected from 412 subjects living in Laoang and Palapag municipalities, Northern Samar, the Philippines. The presence of Schistosoma-specific antibodies in serum samples was tested with the SjSAP4-incorporated GICA strips and the results were converted to fully quantitative data by introducing an R value. The performance of the established GICA was further compared with other diagnostic tools, including the Kato-Katz (KK) technique, point-of-care circulating cathodic antigen (POC-CCA), droplet digital (dd) PCR, and enzyme-linked immunosorbent assays (ELISAs).

Results

The developed GICA strip was able to detect KK positive individuals with a sensitivity of 83.3% and absolute specificity. When calibrated with the highly sensitive faecal ddPCR assay, the immunochromatographic assay displayed an accuracy of 60.7%. Globally, the GICA assay showed a high concordance with the SjSAP4-ELISA assay. The schistosomiasis positivity rate determined by the GICA test was similar to those obtained with the SjSAP4-ELISA assay and the ddPCR assay performed on serum samples (SR_ddPCR), and was 2.3 times higher than obtained with the KK method.

Conclusion

The study further confirms that the developed GICA is a valuable diagnostic tool for detecting light S. japonicum infections and implies that this point-of-care assay is a viable solution for surveying endemic areas of low-intensity schistosomiasis and identifying high-priority endemic areas for targeted interventions.

Development of CRISPR/Cas13a-based assays for the diagnosis of Schistosomiasis

BACKGROUND

Schistosomiasis is a disease that significantly impacts human health in the developing world. Effective diagnostics are urgently needed for improved control of this disease. CRISPR-based technology has rapidly accelerated the development of a revolutionary and powerful diagnostics platform, resulting in the advancement of a class of ultrasensitive, specific, cost-effective and portable diagnostics, typified by applications in COVID-19/cancer diagnosis.

METHODS

We developed CRISPR-based diagnostic platform SHERLOCK (Specific High-sensitivity Enzymatic Reporter unLOCKing) for the detection of Schistosoma japonicum and S. mansoni by combining recombinase polymerase amplification (RPA) with CRISPR-Cas13a detection, measured via fluorescent or colorimetric readouts. We evaluated SHERLOCK assays by using 150 faecal/serum samples collected from Schistosoma-infected ARC Swiss mice (female), and 189 human faecal/serum samples obtained from a S. japonicum-endemic area in the Philippines and a S. mansoni-endemic area in Uganda.

FINDINGS

The S. japonicum SHERLOCK assay achieved 93-100% concordance with gold-standard qPCR detection across all the samples. The S. mansoni SHERLOCK assay demonstrated higher sensitivity than qPCR and was able to detect infection in mouse serum as early as 3 weeks post-infection. In human samples, S. mansoni SHERLOCK had 100% sensitivity when compared to qPCR of faecal and serum samples.

INTERPRETATION

These schistosomiasis diagnostic assays demonstrate the potential of SHERLOCK/CRISPR-based diagnostics to provide highly accurate and field-friendly point-of-care tests that could provide the next generation of diagnostic and surveillance tools for parasitic neglected tropical diseases.

FUNDING

Australian Infectious Diseases Research Centre seed grant (2022) and National Health and Medical Research Council (NHMRC) of Australia (APP1194462, APP2008433).

Development and assessment of a novel gold immunochromatographic assay for the diagnosis of schistosomiasis japonica

Background

The neglected zoonosis, schistosomiasis japonica, remains a major public health problem in the Philippines. The current study aims to develop a novel gold immunochromatographic assay (GICA) and evaluate its performance in the detection of Schistosoma japonicum infection.

Methods

A GICA strip incorporating a S. japonicum saposin protein, SjSAP4 was developed. For each GICA strip test, diluted serum sample (50 µl) was loaded and strips were scanned after 10 min to convert the results into images. ImageJ was used to calculate an R value, which was defined as the signal intensity of the test line divided by the signal intensity of the control line within the cassette. After determination of optimal serum dilution and diluent, the GICA assay was evaluated with sera collected from non-endemic controls (n = 20) and individuals living in schistosomiasis-endemic areas of the Philippines (n = 60), including 40 Kato Katz (KK)-positive participants and 20 subjects confirmed as KK-negative and faecal droplet digital PCR assay (F_ddPCR)-negative at a dilution of 1:20. An ELISA assay evaluating IgG levels against SjSAP4 was also performed on the same panel of sera.

Results

Phosphate-buffered saline (PBS) and 0.9% NaCl were determined as optimal dilution buffer for the GICA assay. The strips tested with serial dilutions of a pooled serum sample from KK-positive individuals (n = 3) suggested that a relatively wide range of dilutions (from 1:10 to 1:320) can be applied for the test. Using the non-endemic donors as controls, the GICA strip showed a sensitivity of 95.0% and absolute specificity; while using the KK-negative and F_ddPCR-negative subjects as controls, the immunochromatographic assay had a sensitivity of 85.0% and a specificity of 80.0%. The SjSAP4-incorperated GICA displayed a high concordance with the SjSAP4-ELISA assay.

Conclusions

The developed GICA assay exhibited a similar diagnostic performance with that of the SjSAP4-ELISA assay, yet the former can be performed by local personnel with minimal training with no requirement for specialised equipment. The GICA assay established here represents a rapid, easy-to-use, accurate and field-friendly diagnostic tool for the on-site surveillance/screening of S. japonicum infection.

Diagnostic performance of a urine-based ELISA assay for the screening of human schistosomiasis japonica: A comparative study

The current study developed and evaluated the performance of a urine-based enzyme-linked immunosorbent assay (ELISA) for the screening of Schistosoma japonicum infection in a human cohort (n = 412) recruited from endemic areas, Northern Samar, the Philippines. The diagnostic performance of the urine ELISA assay was further compared with the Kato-Katz (KK) technique, serum-based ELISA assays, point-of-care circulating cathodic antigen (POC-CCA) urine cassette test, and droplet digital (dd)PCR assays performed on feces, serum, urine, and saliva samples, which were designated as F_ddPCR, SR_ddPCR, U_ddPCR, and SL_ddPCR, respectively. When urine samples concentrated 16× were assessed, the SjSAP4 + Sj23-LHD-ELISA (U) showed sensitivity/specificity values of 47.2/93.8% for the detection of S. japonicum infection in KK-positive individuals (n = 108). The prevalence of S. japonicum infection in the total cohort determined by the urine ELISA assay was 48.8%, which was lower than that obtained with the F_ddPCR (74.5%, p < 0.001), SR_ddPCR (67.2%, p < 0.001), and SjSAP4 + Sj23-LHD-ELISA (S) (66.0%, p < 0.001), but higher than that determined by the Sj23-LHD-ELISA (S) (24.5%, p < 0.001), POC-CCA assay (12.4%, p < 0.001), and SL_ddPCR (25.5%, p < 0.001). Using the other diagnostic tests as a reference, the urine ELISA assay showed a sensitivity between 47.2 and 56.9%, a specificity between 50.7 and 55.2%, and an accuracy between 49.3 and 53.4%. The concentrated urine SjSAP4 + Sj23-LHD-ELISA developed in the current study was more sensitive than both the KK test and POC-CCA assay, and showed a comparable level of diagnostic accuracy to that of the U_ddPCR. However, its diagnostic performance was less robust than that of the F_ddPCR, SR_ddPCR, and SjSAP4 + Sj23-LHD-ELISA (S) assays. Although they are convenient and involve a highly acceptable non-invasive procedure for clinical sample collection, the insufficient sensitivity of the three urine-based assays (the urine ELISA assay, the U_ddPCR test, and the POC-CCA assay) will limit their value for the routine screening of schistosomiasis japonica in the post mass drug administration (MDA) era, where low-intensity infections are predominant in many endemic areas.

Identification of a linear B-cell epitope on the Schistosoma japonicum saposin protein, SjSAP4: Potential as a component of a multi-epitope diagnostic assay

Background

Schistosoma japonicum is one of three major species of blood flukes causing schistosomiasis, a disease, which continues to be a major public health issue in the Philippines. SjSAP4, a member of a multigene family of saposin-like proteins, is a recognized immunodiagnostic biomarker for schistosomiasis japonica. This study aimed to identify linear B-cell epitopes on SjSAP4 and to validate their potential as components of a multi-epitope assay for the serological diagnosis of schistosomiasis japonica.

Methodology

SjSAP4-derived peptides were expressed as GST-peptide-fused proteins and these were Western blot probed with human serum samples from S. japonicum Kato-Katz (KK)-positive individuals and uninfected controls. A core epitope was further identified by Western blotting through probing a series of truncated peptides with the schistosomiasis patient sera. The diagnostic performance of the core epitope-containing peptides and the full-length SjSAP4 was evaluated by enzyme-linked immunosorbent assay (ELISA) using a panel of sera collected from subjects resident in a schistosomiasis-endemic area of the Philippines.

Main findings

As a result of the peptide mapping, one peptide (P15) was found to be highly immunogenic in the KK-positive individuals. We subsequently showed that -S¹⁶³QCSLVGDIFVDKYLD¹⁷⁸- is a core B-cell epitope of P15. Subsequent ELISAs incorporating SjSAP4, SjSAP4-Peptide and SjSP-13V2-Peptide showed a sensitivity of 94.0%, 46.0% and 74.0%, respectively, and a specificity of 97.1%, 100% and 100%, respectively. Notably, complementary recognition of the B-cell epitopes (SjSAP4-Peptide and SjSP-13V2-Peptide) was observed in a subset of the KK-positive individuals. A dual epitope-ELISA (SjSAP4-Peptide + SjSP-13V2-Peptide-ELISA) showed a diagnostic sensitivity of 84.0% and a specificity of 100%.

Conclusions/Significance

In this study, -S¹⁶³QCSLVGDIFVDKYLD¹⁷⁸- was identified as a dominant linear B-cell epitope on SjSAP4. This peptide and the complementary recognition of other B-cell epitopes using sera from different KK-positive individuals can provide the basis of developing a multi-epitope assay for the serological diagnosis of schistosomiasis.

The recent road map (2021–2030) released by WHO for controlling or eliminating neglected tropical diseases (NTDs) highlights diagnostics as a major focus. Development and deployment of accurate, affordable and field-friendly diagnostics/surveillance tools will be crucial for the control and elimination of schistosomiasis. Multi-epitope chimeric antigens, constructed based on linear B-cell epitopes identified from highly antigenic antigens, may achieve not only an equivalent or superior diagnostic performance compared to the parent immunogens but also exhibit more optimal physicochemical properties. However, to date, only a limited number of linear B-cell epitopes have been identified for the serological diagnosis of schistosomiasis. In this study, we identified a linear B-cell epitope (-S¹⁶³QCSLVGDIFVDKYLD¹⁷⁸-) on SjSAP4, a recognized immunodiagnostic biomarker for schistosomiasis japonica, and validated its potential as a component of a multi-epitope assay for the serological diagnosis of schistosomiasis japonica. Notably, differential recognition of B-cell epitopes (SjSAP4-Peptide and SjSP-13V2-Peptide) was observed in a subset of subjects positive by the Kato-Katz technique for the disease. A dual epitope-ELISA (SjSAP4-Peptide + SjSP-13V2-Peptide-ELISA) showed a superior diagnostic performance (84.0% sensitivity and 100% specificity) than individual-epitope ELISAs. The findings in this study provide support for the development of multi-epitope antigen-based diagnostics for schistosomiasis.

The Road to Elimination: Current State of Schistosomiasis Research and Progress Towards the End Game

The new WHO Roadmap for Neglected Tropical Diseases targets the global elimination of schistosomiasis as a public health problem. To date, control strategies have focused on effective diagnostics, mass drug administration, complementary and integrative public health interventions. Non-mammalian intermediate hosts and other vertebrates promote transmission of schistosomiasis and have been utilized as experimental model systems. Experimental animal models that recapitulate schistosomiasis immunology, disease progression, and pathology observed in humans are important in testing and validation of control interventions. We discuss the pivotal value of these models in contributing to elimination of schistosomiasis. Treatment of schistosomiasis relies heavily on mass drug administration of praziquantel whose efficacy is comprised due to re-infections and experimental systems have revealed the inability to kill juvenile schistosomes. In terms of diagnosis, nonhuman primate models have demonstrated the low sensitivity of the gold standard Kato Katz smear technique. Antibody assays are valuable tools for evaluating efficacy of candidate vaccines, and sera from graded infection experiments are useful for evaluating diagnostic sensitivity of different targets. Lastly, the presence of Schistosomes can compromise the efficacy of vaccines to other infectious diseases and its elimination will benefit control programs of the other diseases. As the focus moves towards schistosomiasis elimination, it will be critical to integrate treatment, diagnostics, novel research tools such as sequencing, improved understanding of disease pathogenesis and utilization of experimental models to assist with evaluating performance of new approaches.

Laboratory Evaluation of a Basic Recombinase Polymerase Amplification (RPA) Assay for Early Detection of Schistosoma japonicum

Early detection of Schistosoma japonicum (S. japonicum) within its intermediate and definitive hosts is crucial for case finding and disease surveillance, especially in low-endemic areas. Recombinase polymerase amplification (RPA) has many advantages over traditional methods of DNA-amplification, such as polymerase chain reaction (PCR), including high sensitivity and specificity whilst being deployable in resource-poor schistosomiasis-endemic areas. Here, we evaluated the performance of a basic RPA assay targeting the 28srDNA gene fragment of S. japonicum (Sj28srDNA) using schistosome-infected Oncomelania hupensis (O. hupensis) and mouse models, compared to the traditional pathological method and a PCR assay. Overall S. japonicum infection prevalence within O. hupensis hosts by microscopic dissection, PCR and RPA was 9.29% (13/140), 32.14% (45/140) and 51.43% (72/140), respectively, presenting significant differences statistically (χ2 = 58.31, p < 0.001). It was noteworthy that infection prevalence by PCR and RPA performed was 34.44% (31/90) and 53.33% (48/90) in snails within 6 weeks post-infection, while the dissection method detected all samples as negatives. In addition, the basic RPA assay presented positive results from the fourth week post-infection and third day post-infection when detecting fecal DNA and serum DNA, respectively, which were extracted from a pooled sample from mice infected with 20 S. japonicum cercariae. This study suggests that the RPA assay has high potential for early detection of S. japonicum infection within its intermediate and definitive hosts.

Membrane Technology for Rapid Point-of-Care Diagnostics for Parasitic Neglected Tropical Diseases

Parasitic neglected tropical diseases (NTDs) affect over one billion people worldwide, with individuals from communities in low-socioeconomic areas being most at risk and suffering the most. Disease management programs are hindered by the lack of infrastructure and resources for clinical sample collection, storage, and transport and a dearth of sensitive diagnostic methods that are inexpensive as well as accurate. Many diagnostic tests and tools have been developed for the parasitic NTDs, but the collection and storage of clinical samples for molecular and immunological diagnosis can be expensive due to storage, transport, and reagent costs, making these procedures untenable in most areas of endemicity. The application of membrane technology, which involves the use of specific membranes for either sample collection and storage or diagnostic procedures, can streamline this process, allowing for long-term sample storage at room temperature. Membrane technology can be used in serology-based diagnostic assays and for nucleic acid purification prior to molecular analysis. This facilitates the development of relatively simple and rapid procedures, although some of these methods, mainly due to costs, lack accessibility in low-socioeconomic regions of endemicity. New immunological procedures and nucleic acid storage, purification, and diagnostics protocols that are simple, rapid, accurate, and cost-effective must be developed as countries progress control efforts toward the elimination of the parasitic NTDs.

Performance of the point-of-care circulating cathodic antigen test in the diagnosis of schistosomiasis japonica in a human cohort from Northern Samar, the Philippines

BACKGROUND

Zoonotic schistosomiasis, caused by Schistosoma japonicum, remains a major public health problem in the Philippines. This study aimed to evaluate the commercially available rapid diagnostic point-of-care circulating cathodic antigen (POC-CCA) test in detecting individuals infected with S. japonicum in a human cohort from an endemic area for schistosomiasis japonica in the Philippines.

METHODS

Clinical samples were collectedin 18 barangays endemic for S. japonicum infection in Laoang and Palapag municipalities, Northern Samar, the Philippines, in 2015. The presence of CCA in filter-concentrated urine samples (n = 412) was evaluated using the commercial kits and the results were converted to images, which were further analyzed by ImageJ software to calculate R values. The diagnostic performance of the immunochromatographic POC-CCA test was compared using the Kato-Katz (KK) procedure, in-house enzyme-linked immunosorbent assays (ELISAs) and droplet digital (dd) PCR assays as reference.

RESULTS

The POC-CCA test was able to detect S. japonicum-infected individuals in the cohort with an eggs per gram of faeces (EPG) more than or equal to 10 with sensitivity/specificity values of 63.3%/93.3%. However, the assay showed an inability to diagnose schistosomiasis japonica infections in all cohort KK-positive individuals, of which the majority had an extremely low egg burden (EPG: 1-9). The prevalence of S. japonicum infection in the total cohort determined by the POC-CCA test was 12.4%, only half of that determined by the KK method (26.2%). When compared with the ELISAs and ddPCR assays as a reference, the POC-CCA assay was further shown to be a test with low sensitivity. Nevertheless, the assay exhibited significant positive correlations with egg burden determined by the KK technique and the target gene copy number index values determined by the ddPCR assays within the entire cohort.

CONCLUSIONS

By using in silico image analysis, the POC-CCA cassette test could be converted to a quantitative assay to avoid reader-variability. Because of its low sensitivity, the commercially available POC-CCA assay had limited potential for determining the status of a S. japonicum infection in the target cohort. The assay should be applied with caution in populations where schistosome parasites (especially S. japonicum) are present at low infection intensity.

Parasitic Helminth-Derived microRNAs and Extracellular Vesicle Cargos as Biomarkers for Helminthic Infections

As an adaption to their complex lifecycles, helminth parasites garner a unique repertoire of genes at different developmental stages with subtle regulatory mechanisms. These parasitic worms release differential components such as microRNAs (miRNAs) and extracellular vesicles (EVs) as mediators which participate in the host-parasite interaction, immune regulation/evasion, and in governing processes associated with host infection. MiRNAs are small (~ 22-nucleotides) non-coding RNAs that regulate gene expression at the post-transcriptional level, and can exist in stable form in bodily fluids such as serum/plasma, urine, saliva and bile. In addition to reports focusing on the identification of miRNAs or in the probing of differentially expressed miRNA profiles in different development stages/sexes or in specific tissues, a number of studies have focused on the detection of helminth-derived miRNAs in the mammalian host circulatory system as diagnostic biomarkers. Extracellular vesicles (EVs), small membrane-surrounded structures secreted by a wide variety of cell types, contain rich cargos that are important in cell-cell communication. EVs have attracted wide attention due to their unique functional relevance in host-parasite interactions and for their potential value in translational applications such as biomarker discovery. In the current review, we discuss the status and potential of helminth parasite-derived circulating miRNAs and EV cargos as novel diagnostic tools.

Understanding the Pathophysiology of Exosomes in Schistosomiasis: A New Direction for Disease Control and Prevention

Schistosomiasis is a parasitic disease endemic to freshwater areas of Southeast Asia, Africa, and South America that is capable of causing serious damage to the internal organs. Recent studies have linked exosomes to the progression of schistosomiasis. These structures are important mediators for intercellular communication, assist cells to exchange proteins, lipids, and genetic material and have been shown to play critical roles during host–parasite interactions. This review aims to discuss the pathophysiology of exosomes in schistosomiasis and their roles in regulating the host immune response. Understanding how exosomes are involved in the pathogenesis of schistosomiasis may provide new perspectives in diagnosing and treating this neglected disease.

Potential of antibody test using Schistosoma mansoni recombinant serpin and RP26 to detect light-intensity infections in endemic areas

Schistosomiasis remains a worldwide public health problem, especially in sub-Saharan Africa. The World Health Organization targets the goal for its elimination as a public health problem in the 2030 Neglected Tropical Diseases (NTDs) Roadmap. Concerted action and agile responses to challenges will be necessary to achieve the targets. Better diagnostic tests can accelerate progress towards the elimination by monitoring disease trends and evaluating the effectiveness of interventions; however, current examinations such as Kato-Katz technique are of limited power to detect light-intensity infections. The point-of-care circulating cathodic antigen (POC-CCA) test shows a higher sensitivity compared to the reference standard, Kato-Katz technique, but it still lacks sufficient sensitivity with low infection intensity. In this study, we examined antibody reactions against recombinant protein antigens; Schistosoma mansoni serine protease-inhibitor (SmSerpin) and RP26, by enzyme-linked immunosorbent assay (ELISA) in plasma samples with light-intensity infection. The sensitivity using the cocktail antigen of recombinant SmSerpin and RP26 showed 83.7%. The sensitivity using S. mansoni soluble egg antigen (SmSEA) was 90.8%, but it showed poor specificity (29.7%), while the cocktail antigen presented improved specificity (61.4%). We conclude that antibody detection to the SmSerpin and RP26 protein antigens is effective to detect S. mansoni light-intensity infections. Our study indicates the potential of detecting antibody against recombinant protein antigens to monitor the transmission of schistosomiasis in low endemicity contexts.

Schistosome Infection and Schistosome-Derived Products as Modulators for the Prevention and Alleviation of Immunological Disorders

Parasitic helminths, comprising the flatworms (tapeworms and flukes) and nematodes (roundworms), have plagued humans persistently over a considerable period of time. It is now known that the degree of exposure to these and other pathogens inversely correlates with the incidence of both T helper 1 (Th1)-mediated autoimmunity and Th2-mediated allergy. Accordingly, there has been recent increased interest in utilizing active helminth worm infections and helminth-derived products for the treatment of human autoimmune and inflammatory diseases and to alleviate disease severity. Indeed, there is an accumulating list of novel helminth derived molecules, including proteins, peptides, and microRNAs, that have been shown to exhibit therapeutic potential in a variety of disease models. Here we consider the blood-dwelling schistosome flukes, which have evolved subtle immune regulatory mechanisms that promote parasite survival but at the same time minimize host tissue immunopathology. We review and discuss the recent advances in using schistosome infection and schistosome-derived products as therapeutics to treat or mitigate human immune-related disorders, including allergic asthma, arthritis, colitis, diabetes, sepsis, cystitis, and cancer.

Schistosoma japonicum Infection in Treg-Specific USP21 Knockout Mice

The E3 deubiquitinating enzyme ubiquitin-specific proteolytic enzyme 21 (USP21) plays vital roles in physiological activities and is required for Treg-cell-mediated immune tolerance. Using a murine model infected with Schistosoma japonicum, we observed that there were more cercariae developed into adults and more eggs deposited in the livers of the USP21^fl/flFOXP3^Cre (KO) mice. However, immunohistochemistry showed that the degree of egg granuloma formation and liver fibrosis was reduced. In USP21^fl/flFOXP3^Cre mice, levels of IFN-gamma, IL-4, anti-soluble egg antigen (SEA) IgG and anti-soluble worm antigen preparation (SWAP) IgG increased in blood, as determined using ELISAs and multiplex fluorescent microsphere immunoassays, while the levels of IL-10, lL-17A, IL-23, IL-9, and anti-SEA IgM decreased. In addition, the levels of the USP21 protein and mRNA in the liver and spleen of KO mice decreased. We further observed increased Th1 responses amplified by Tregs (regulatory T cells) and compromised Th17 responses, which alleviated the liver immunopathology. We speculated that these changes were related to polarization of Th1-like Tregs. Our results revealed the roles of USP21 in Treg-cell-mediated regulation of immune interactions between Schistosoma and its host. USP21 may have potential for regulating hepatic fibrosis in patients with schistosomiasis.

Reviews and advances in diagnostic research on Schistosoma japonicum

Schistosomiasis is an acute and chronic parasitic disease caused by blood flukes (trematode worms) of the genus Schistosoma. Schistosoma japonicum (S. japonicum) infection has decreased significantly in prevalence and intensity of infection in China. However, this disease still remains a serious public health problem in some endemic areas of the Philippines and Indonesia. Thus, more accurate and sensitive methods are much needed for further control of this disease. Here, we review the research progress in techniques for the diagnosis of S. japonicum infection.

Analyses of the expression, immunohistochemical properties and serodiagnostic potential of Schistosoma japonicum peroxiredoxin-4

Background

Schistosoma japonicum, which inhabits the mesenteric vein of the mammalian hosts for about 20 to 30 years, is subjected to the oxidative stresses from the host defense mechanism during their intra-mammalian stages. To counteract this host immune attack, the parasite utilizes their antioxidant system for survival inside the host. Peroxiredoxins (Prxs), thiol-specific antioxidant proteins, play an essential role for protecting the parasite against oxidative stress by reducing hydrogen peroxide to water. Only three types of 2-Cys Prxs have been previously characterized in S. japonicum whereas a fourth Prx has been identified for Schistosoma mansoni as Prx-4. A sequence coding homologous to this gene in the S. japonicum database was identified, characterized and expressed as recombinant SjPrx-4 protein (rSjPrx-4). Furthermore, rSjPrx-4 was evaluated in this study for its diagnostic potentials in detecting S. japonicum infection in humans.

Results

The gene found in the parasite genome contained 2 active-site cysteines with conserved sequences in the predicted amino acid (AA) sequence and showed 75% identity with that of the previously characterized Prx (TPx-1) of S. japonicum. The gene was expressed in different stages of schistosome life-cycle with highest transcription level in the adult male. The gene was cloned into a plasmid vector and then transfected into Escherichia coli for expression of rSjPrx-4. Anti-rSjPrx-4 mouse sera recognized native SjPrx-4 in egg and adult worm lysate by western blotting. The result of a mixed function oxidation assay in which rSjPrx-4 prevented the nicking of DNA from hydroxyl radicals confirmed its antioxidant activity. Subsequently, immunolocalization analysis showed the localization of SjPrx-4 inside the egg, on the tegument and in the parenchyma of the adult worm. Enzyme-linked immunosorbent assay results showed that rSjPrx-4 has 83.3% sensitivity and 87.8% specificity. Its diagnostic potential was further evaluated in combination with recombinant SjTPx-1 protein, yielding an improved sensitivity and specificity of 90% and 92.7%, respectively.

Conclusions

These results suggest that SjPrx-4 plays a role as an antioxidant dealing with oxidative stresses of S. japonicum, and its diagnostic potential improved by coupling it with SjTPx-1 is a proof for developing a serological test with better diagnostic performance for human schistosomiasis.

Humoral responses to Schistosoma japonicum soluble egg antigens in domestic animals in Lindu Subdistrict, Central Sulawesi Province, Indonesia

Background and Aim: Schistosomiasis japonica, a disease caused by Schistosoma japonicum, is a public health problem in the Philippines, the Republic of Indonesia, and the People's Republic of China. The disease is known as zoonotic, meaning other than humans, animals are involved as the reservoirs. In Indonesia, schistosomiasis surveillance in animals is not continuous. Thus, the study to determine the prevalence of the disease in animals is needed. The study was aimed to determine the seroprevalence of S. japonicum infection among four species of domestic animals in the Lindu Sub-district, Central Sulawesi Province of Indonesia. Materials and Methods: Blood samples of domestic animals were collected and analyzed for the presence of anti-S. japonicum immunoglobulin G antibodies against S. japonicum soluble egg antigens using the indirect hemagglutination assay. Animal stool samples were collected, and the miracidia-hatching assay was used for the detection of S. japonicum infection. Additional data concerning the animal identity and the management practices were obtained through a questionnaire used in surveys and interviews. Results: A total of 146 sera from 13 cattle, 24 buffaloes, 54 pigs, and 55 dogs were collected. The overall schistosomiasis seroprevalence was 64.4%. The serology prevalence in cattle, buffalo, pig, and dog was 100.0%, 41.7%, 74.1%, and 56.4%, respectively. Domestic animals in all of five villages have previous exposure with S. japonicum as seropositive animals detected in every village. A total of 104 animal stool samples from 146 animals sampled were obtained. The overall schistosomiasis prevalence determined by the miracidia hatching assay was 16.35%. The sensitivity and specificity of indirect hemagglutination assay (IHA) in the current study were 88.24% and 41.37%, respectively, with miracidia hatching assay as the gold-standard method. Conclusion: This study has shown a high seroprevalence of schistosomiasis japonica among domestic animals in the Lindu Subdistrict. IHA can be used as the screening method for the detection of S. japonicum infection in domestic animals. Chemotherapy and animal livestock grazing management programs to reduce the parasite burden and Schistosoma egg contamination in the environment must be implemented as part of one health approaches, in addition to other control measures.

Screening of a library of recombinant Schistosoma mansoni proteins with sera from murine and human controlled infections identifies early serological markers

Background

Schistosomiasis is a major global health problem caused by blood-dwelling parasitic worms, which is currently tackled primarily by mass administration of the drug praziquantel. Appropriate drug treatment strategies are informed by diagnostics that establish the prevalence and intensity of infection, which, in regions of low transmission, should be highly sensitive.

Methods

To identify sensitive new serological markers of Schistosoma mansoni infections, we have compiled a recombinant protein library of parasite cell-surface and secreted proteins expressed in mammalian cells.

Results

Together with a time series of sera samples from volunteers experimentally infected with a defined number of male parasites, we probed this protein library to identify several markers that can detect primary infections with as low as 10 parasites and as early as 5 weeks postinfection.

Conclusions

These new markers could be further explored as valuable tools to detect ongoing and previous S mansoni infections, including in endemic regions where transmission is low.

Serum Exosomal miRNAs for Grading Hepatic Fibrosis Due to Schistosomiasis

Chronic infection with Schistosoma japonicum or Schistosoma mansoni results in hepatic fibrosis of the human host. The staging of fibrosis is crucial for prognosis and to determine the need for treatment of patients with schistosomiasis. This study aimed to determine whether there is a correlation between the levels of serum exosomal micro-ribonucleic acids (miRNAs) (exomiRs) and fibrosis progression in schistosomiasis. Reference gene (RG) validation was initially carried out for the analysis of serum exomiRs expression in staging liver fibrosis caused by schistosome infection. The expression levels of liver fibrosis-associated exomiRs in serum were determined in a murine schistosomiasis model and in a cohort of Filipino schistosomiasis japonica patients (n = 104) with different liver fibrosis grades. Of twelve RG candidates validated, miR-103a-3p and miR-425-5p were determined to be the most stable genes in the murine schistosomiasis model and subjects from the schistosomiasis-endemic area, respectively. The temporal expression profiles of nine fibrosis-associated serum exomiRs, as well as their correlations with the liver pathologies, were determined in C57BL/6 mice during S. japonicum infection. The serum levels of three exomiRs (miR-92a-3p, miR-146a-5p and miR-532-5p) were able to distinguish subjects with fibrosis grades I-III from those with no fibrosis, but only the serum level of exosomal miR-146a-5p showed potential for distinguishing patients with mild (grades 0–I) versus severe fibrosis (grades II–III). The current data imply that serum exomiRs can be a supplementary tool for grading liver fibrosis in hepatosplenic schistosomiasis with moderate accuracy.

Recombinant micro-exon gene 3 (MEG-3) antigens from Schistosoma mansoni failed to induce protection against infection but show potential for serological diagnosis

Sequence databases on Schistosoma mansoni have revealed micro-exon gene (MEGs) families. Many of these genes are highly expressed in parasite life cycle stages associated with the mammalian host infection and appear to be involved in immune evasion by schistosomes. So, we believe that MEG-coding proteins would make potential candidates for vaccine development or diagnosis for schistosomiasis. Here, we study MEG-3.2 and MEG-3.4, members of the MEG-3 family. Recombinant (r) proteins were produced and formulated with Freund's adjuvant for vaccination of mice. Immunization with recombinant MEG-3.2 or MEG-3.4 formulation generated high levels of IgG1 antibodies. Additionally, vaccination also induced a mixed Th1/Th2/Th17-type of response, since IFN-γ, IL-5 and IL-17 cytokines were detected in the supernatant of spleen cell cultures; however it failed to induce reduction in parasitic worm burden. Finally, the recombinant proteins were evaluated in a serological assay using human samples. Schistosome-infected individuals showed higher levels of both IgG and IgM against rMEG-3.2 compared to non-infected individuals, while only IgM anti-rMEG-3.4 antibodies were elevated in infected patients. Therefore, between both studied molecules, MEG-3.2 protein is the antigen that shows potential to compose a serological diagnosis test for schistosomiasis.

Preliminary evaluation of the diagnostic potential of Schistosoma japonicum extracellular vesicle proteins for Schistosomiasis japonica

Schistosomiasis is a chronic parasitic disease caused by the genus Schistosoma and poses a great threat to human and animal health. Identification of effective biomarkers would facilitate evaluation of drug efficacy and recognition of infected hosts, which are crucial for effective schistosomiasis control. Extracellular vesicle (EV) proteins are considered ideal biomarkers for developing invasive diagnostic tools. In this study, we evaluated the potential of Schistosoma japonicum EV (SjEV) proteins as biomarkers for diagnosing schistosomiasis. Several SjEV proteins were subject to epitope prediction using DNASTAR software, and the diagnostic potential of selected peptides was evaluated using enzyme-linked immunosorbent assay (ELISA). The results indicated that the sera showed detectable antibody levels against the two antigens in mice, rabbits, and humans infected with S. japonicum. Further analysis of the combined epitope protein demonstrated a modest sensitivity for detection of Schistosomiasis japonica. Our preliminary study suggests that S. japonicum EV proteins could serve as potential biomarkers for developing diagnostic tools for schistosomiasis.

Parasite-derived circulating microRNAs as biomarkers for the detection of human Schistosoma japonicum infection

Novel tools for early diagnosis and monitoring of schistosomiasis are urgently needed. This study aimed to validate parasite-derived miRNAs as potential novel biomarkers for the detection of human Schistosoma japonicum infection. A total of 21 miRNAs were initially validated by real-time-polymerase chain reaction (RT-PCR) using serum samples of S. japonicum-infected BALB/c mice. Of these, 6 miRNAs were further validated with a human cohort of individuals from a schistosomiasis-endemic area of the Philippines. RT-PCR analysis showed that two parasite-derived miRNAs (sja-miR-2b-5p and sja-miR-2c-5p) could detect infected individuals with low infection intensity with moderate sensitivity/specificity values of 66%/68% and 55%/80%, respectively. Analysis of the combined data for the two parasite miRNAs revealed a specificity of 77.4% and a sensitivity of 60.0% with an area under the curve (AUC) value of 0.6906 (P = 0.0069); however, a duplex RT-PCR targeting both sja-miR-2b-5p and sja-miR-2c-5p did not result in an increased diagnostic performance compared with the singleplex assays. Furthermore, the serum level of sja-miR-2c-5p correlated significantly with faecal egg counts, whereas the other five miRNAs did not. Targeting S. japonicum-derived miRNAs in serum resulted in a moderate diagnostic performance when applied to a low schistosome infection intensity setting.

The soluble worm antigens-specific antibodies used as biomarkers of Schistosoma japonicum in a low prevalence and intensity endemic area of Hubei, China

The precise diagnosis of Schistosoma japonicum (S. japonicum) infection plays a critical role in achieving the ultimate goal of eliminating schistosomiasis in endemic regions. We evaluated the S. japonicum soluble worm antigen protein (SWAP) specific-IgG, IgG4 and IgE levels, and evaluated the association between S. japonicum infection and these antibodies in a sample of 837 residents from a S. japonicum-endemic area in Hubei province, China. The anticipants were divided into the Training Set (TS) and Validation Set (VS) based on the chronological order. Enzyme-linked immunosorbent assays were performed to detect the SWAP-specific antibodies. Three algorithms for identifying S. japonicum infection were generated in the TS and subsequently validated in the VS. The findings were further replicated in an independent cohort from an endemic area for Schistosoma mansoni (S. mansoni) in Brazil. Our results indicated for the first time that S. japonicum-infected individuals had higher levels of SWAP-specific IgG, IgG4 and IgE, and lower value of the IgE/IgG4 ratio than uninfected individuals in both the two sets (p <  0.01). Both the infected and uninfected individuals had a high prevalence of seropositivity for IgG. We further showed that the predictive model EGR (IgE/IgG4 ratio) score performed best in Chinese population (area under the receiver operating characteristic (AUROC) 0.905, sensitivity 82.7%, specificity 84.0% in the TS; AUROC 0.933, sensitivity 87.7%, specificity 89.1% in the VS). Nevertheless, the predictive model IgG4 score performed best in Brazilian cohort (AUROC 0.788, sensitivity 73.2%, specificity 73.3%). In summary, SWAP-specific IgG could be used as a biomarker for identifying individuals who have been previously exposed to S. japonicum, and furthermore the SWAP-specific IgE/IgG4 could be used as an immune biomarker for S. japonicum infection in particular in the endemic areas with low prevalence and intensity.

Comparison of Kato Katz, antibody-based ELISA and droplet digital PCR diagnosis of schistosomiasis japonica: Lessons learnt from a setting of low infection intensity

Background

Zoonotic schistosomiasis in Asia, caused by Schistosoma japonicum, remains a major public health concern in China and the Philippines. The developing epidemiological and socio-economic picture of the disease in endemic areas necessitates the development of affordable and highly accurate field diagnostics as an important component in evaluating ongoing integrated control and elimination efforts.

Methods

Three diagnostic methods, namely Kato-Katz (KK) stool microscopy, ELISA and droplet digital (dd) PCR assays, were compared by detecting infection in a total of 412 participants from an area moderately endemic for schistosomiasis in the Philippines.

Results

This comprehensive comparison further defined the diagnostic performance and features for each assay. Compared with the ddPCR assay analysing DNA from faeces (F_ddPCR), which exhibited the highest sensitivity, the SjSAP4 + Sj23-LHD-ELISA had the best accuracy (67.2%) among all five ELISA assays assessed. Schistosomiasis prevalence determined by the SjSAP4 + Sj23-LHD-ELISA and ddPCRs was similar and was at least 2.5 times higher than obtained with the KK method. However, the agreement between these assays was low. In terms of cost and logistical convenience, the SjSAP4 + Sj23-LHD-ELISA represents a cost-effective assay with considerable diagnostic merits. In contrast, although the ddPCR assays exhibited a high level of diagnostic performance, the high cost and the need for specialized equipment presents a major obstacle in their application in screening campaigns.

Conclusion

The SjSAP4 + Sj23-LHD-ELISA represents a cost-effective tool for the diagnosis of schistosomiasis that could prove an important component in the monitoring of integrated control measures as elimination draws closer, whereas the ddPCR assays, in addition to their high sensitivity and specificity, are capable of quantifying infection intensity. However, the high cost of ddPCR hinders its wider application in screening programs, although it could be a valuable reference in the development and improvement of other diagnostic assays.

Schistosomiasis japonica remains prevalent in China and in the Philippines. The current changes in the epidemiological and socio-economic picture in the endemic areas makes it imperative that affordable and more sensitive field diagnostics are developed as an important component to evaluate ongoing integrated control and elimination efforts. Three diagnostic approaches, namely Kato-Katz stool microscopy, ELISA and droplet digital PCR assays, were compared by detecting infection in a cohort from schistosome-endemic areas in the Philippines. This comprehensive comparison further defined the diagnostic performance and features for each assay. Prevalence of schistosomiasis determined by the SjSAP4 + Sj23-LHD-ELISA and ddPCRs was at least 2.5 times higher than that by the KK method. The prevalence determined by the SjSAP4 + Sj23-LHD-ELISA and ddPCRs was similar, but low agreements between these assays were evident. The ddPCR assays showed considerable diagnostic performance but the high associated costs and the need for specialized equipment present major obstacles in their application in screening campaigns although they can serve as reference standards for evaluating other diagnostic assays. The SjSAP4 + Sj23-LHD-ELISA represents a cost-effective tool for the diagnosis of schistosomiasis japonica and this assay could prove an important monitoring tool to evaluate the impact of integrated control measures over time.

Asian Schistosomiasis: Current Status and Prospects for Control Leading to Elimination

Schistosomiasis is an infectious disease caused by helminth parasites of the genus Schistosoma. Worldwide, an estimated 250 million people are infected with these parasites with the majority of cases occurring in sub-Saharan Africa. Within Asia, three species of Schistosoma cause disease. Schistosoma japonicum is the most prevalent, followed by S. mekongi and S. malayensis. All three species are zoonotic, which causes concern for their control, as successful elimination not only requires management of the human definitive host, but also the animal reservoir hosts. With regard to Asian schistosomiasis, most of the published research has focused on S. japonicum with comparatively little attention paid to S. mekongi and even less focus on S. malayensis. In this review, we examine the three Asian schistosomes and their current status in their endemic countries: Cambodia, Lao People's Democratic Republic, Myanmar, and Thailand (S. mekongi); Malaysia (S. malayensis); and Indonesia, People's Republic of China, and the Philippines (S. japonicum). Prospects for control that could potentially lead to elimination are highlighted as these can inform researchers and disease control managers in other schistosomiasis-endemic areas, particularly in Africa and the Americas.

Circulating miRNAs as footprints for liver fibrosis grading in schistosomiasis

BACKGROUND

Chronic infection with Schistosoma japonicum or S. mansoni results in hepatic fibrosis of the human host. Staging fibrosis is crucial for the prognosis and to determine the rapid need of treatment in patients with schistosomiasis.

METHODS

To establish whether there is a correlation between circulating microRNA (miRNA) level and fibrosis progression in schistosomiasis, ten miRNAs were selected to assess their potential in grading schistosomiasis liver fibrosis. This was done firstly in two mouse strains (C57BL/6 and BALB/c) to determine the temporal expression profiles in serum over the course of S. japonicum infection, and then within a cohort of 163 schistosomiasis japonica patients with different grades of liver fibrosis.

FINDING

Four miRNAs (miR-150-5p, let-7a-5p, let-7d-5p and miR-146a-5p) were able to distinguish patients with mild versus severe fibrosis. The level of serum miR-150-5p showed the most promising potential for grading hepatic fibrosis in schistosomiasis. The diagnostic performance of miR-150-5p in discriminating mild from severe fibrosis is comparable with that of the ELF test and serum HA level. In addition, the serum levels of the four miRNAs rebounded in infected C57BL/6 mice, after 6 months post treatment, following the regression of liver fibrosis, thereby providing further support for the utility of these miRNAs in grading schistosomal hepatic fibrosis.

INTERPRETATION

Circulating miRNAs can be a supplementary tool for assessing hepatic fibrosis in human schistosomiasis. FUND: National Health and Medical Research Council (NHMRC) of Australia (APP1102926, APP1037304 and APP1098244).

Protective Immune Responses Generated in a Murine Model Following Immunization with Recombinant Schistosoma japonicum Insulin Receptor

There is a pressing need to develop vaccines for schistosomiasis given the current heavy dependency on praziquantel as the only available drug for treatment. We previously showed the ligand domain of the Schistosoma japonicum insulin receptor 1 and 2 (rSjLD1 and 2) fusion proteins conferred solid protection in mice against challenge infection with S. japonicum. To improve vaccine efficacy, we compared the immunogenicity and protective efficacy of rSjLD1 on its own and in combination with S. japonicum triose-phosphate isomerase (SjTPI), formulated with either of two adjuvants (QuilA and montanide ISA 720VG) in murine vaccine trials against S. japonicum challenge. The level of protection was higher in mice vaccinated only with rSjLD1 formulated with either adjuvant; rSjTPI or the rSjTPI-rSjLD1 combination resulted in a lower level of protection. Mirroring our previous results, there were significant reductions in the number of female worms (30–44%), faecal eggs (61–68%), liver eggs (44–56%), intestinal eggs (46–48%) and mature intestinal eggs (58–63%) in the rSjLD1-vaccinated mice compared with the adjuvant only groups. At 6-weeks post-cercarial challenge, a significantly increased production of interferon gamma (IFNγ) in rSjLD1-stimulated splenic CD4⁺ T cells was observed in the rSjLD1-vaccinated mice suggesting a Th1-type response is associated with the generated level of protective efficacy.

Suppression of Schistosoma japonicum Acetylcholinesterase Affects Parasite Growth and Development

To further investigate the importance of Schistosoma japonicum acetylcholinesterase (SjAChE) in cholinergic signaling for parasite growth and development, we used RNA interference (RNAi) to knock-down its expression in adults and eggs in vitro. This resulted in its reduced transcription but also expression of other important genes involved both in cholinergic signaling and glucose uptake were impacted substantially. Significant decreases in AChE protein expression, AChE enzymatic activity, and glucose uptake were observed in the SjAChE-knockdown parasites compared with luciferase controls. In vaccine/challenge experiments, we found that immunization of mice with recombinant SjAChE (rSjAChE) expressed in Escherichia coli elicited reductions in male worm numbers (33%), liver granuloma density (41%), and reduced numbers of mature intestinal eggs (73%) in the vaccinated group compared with the control group. These results indicate AChE plays an important role in the metabolism of male worms, and impacts indirectly on female fecundity leading to increased numbers of immature eggs being released and reduced sizes of liver granulomas. Furthermore, cytokine analysis showed that immunization of mice with rSjAChE elicited a predominantly Th1-type immune response characterized by increased production of IFNγ in splenic CD4⁺ T cells of vaccinated mice. The study confirms the potential of SjAChE as a vaccine/drug candidate against zoonotic schistosomiasis japonica.

Effects of Polymorphisms in the SjSP-13 Gene of Schistosoma japonicum on Its Diagnostic Efficacy and Immunogenicity

Schistosomiasis japonica is one of the most prevalent parasitic diseases in China. The scarcity of effective diagnostic tools is a major factor that contributes to the high prevalence of schistosomiasis japonica. SjSP-13 is a promising serological diagnostic biomarker of the disease. However, it is unclear whether polymorphisms in SjSP-13 affect its diagnostic efficacy and immunogenicity. Here, we found the SjSP-13 gene was highly polymorphic, and all the alleles of the gene were clustered into two clades, clade A and B. SjSP-13.6 and SjSP-13.25, the representative alleles of clade A and B, were produced in Escherichia coli. The diagnostic value of SjSP-13.6 (AUC = 0.983 ± 0.006), was found to be similar to the SjSP-13.25 (AUC = 0.973 ± 0.009) by receiver operating characteristic (ROC) analysis. SjSP-13.6 and SjSP-13.25 have the same specificity (96.7%), while the sensitivity of SjSP-13.6 (90.4%) is slightly but not significantly higher than SjSP-13.25 (85.2%). The combination use of the two alleles (SjSP-13.6/25) didn’t increase the diagnostic performance of SjSP-13 as the AUC value of SjSP-13.6/25 is 0.977 ± 0.009, lower than individual SjSP-13.6 (AUC = 0.983 ± 0.006). In addition, we found the immunogenicity of clade A alleles is significantly higher than clade B in Schistosoma japonicum naturally infected animals and patients, as the mean antibody levels of SjSP-13.6 was significantly higher than SjSP-13.25. We conclude that polymorphisms of the SjSP-13 gene should not affect its diagnostic efficacy, and it is not necessary to combine the alleles of the two clades for diagnosis of schistosomiasis.

A perspective for improving the sensitivity of detection: The application of multi-epitope recombinant antigen in serological analysis of buffalo schistosomiasis

The sensitivity and specificity are two crucial aspects of addressing the efficacy of diagnostic antigens. Achilles' heel of low sensitivity rate exists in current diagnostic recombinant antigens for schistosomiasis detection. This study focused on the diagnosis of water buffalo schistosomiasis japonica and a perspective of improving recombinant antigens' sensitivity was assessed using archived 220 water buffalo sera (114 positive sera, 92 negative sera and 14 Paramphistomum-infected sera) and the method of enzyme-linked immunosorbent assay (ELISA). The subjects included two trivalent recombinant proteins, one bivalent antigen and two single-molecular antigens. The crude antigen SEA (soluble egg antigen) was employed as reference antigen. The highest sensitivity rate in the five recombinant antigens assigned to the trivalent multi-epitope antigen PA4 (95.61%, 109/114), no significant difference with SEA (100%, 114/114, p = .836), and showing remarkable differences with the two single-molecular antigens (p < 0.01). In term of specificity, two trivalent multi-epitope antigens PA4 (97.83%, 90/92), PA5 (100%, 92/92) and the bivalent antigen PA3 (98.91%, 91/92) had few differences with one monovalent antigens PA1 (97.83%, 90/92, p = .304/0.103/0.640), significant differences with another monovalent antigens PA2 (92.39%, 85/92, p < 0.01) and SEA (82.61%, 76/92, p < 0.01). Additional, all the recombinant antigens had low cross-reactivity (7.14%, 1/14, 0% for PA5) with serum samples of paramphistomiasis, contrast with that of SEA (50%, 7/14, p < 0.01). The results indicated that multi-epitope antigens have the possibility to improve diagnostic sensitivity and the trivalent multi-epitope antigen PA4 possesses greater likelihood to be a diagnostic antigen for water buffalo schistosomiasis.

Diagnosis of schistosomiasis mansoni: an evaluation of existing methods and research towards single worm pair detection

The inadequacy of current diagnostics for the detection of low worm burdens in humans means that schistosomiasis mansoni is more widespread than previously acknowledged. With the inception of mass drug treatment programmes aimed at disease elimination and the advent of human vaccine trials, the need for more sensitive diagnostics is evident. In this review, we evaluate the merits and limitations of the principal diagnostic methods, namely detection of eggs in faeces; anti-schistosome antibodies in serum; parasite-derived proteins and glycans in serum or urine; parasite DNA in blood, faeces or urine. Only in the baboon model, where actual worm burden is determined by portal perfusion, have faecal smear and circulating antigen methods been calibrated, and shown to have thresholds of detection of 10-19 worm pairs. There is scope for improvement in all the four methods of detection, e.g. the identification of single targets for host antibodies to improve the specificity of enzyme linked immunosorbent assay. Despite recent advances in the definition of the schistosome secretome, there have been no comprehensive biomarker investigations of parasite products in the urine of infected patients. Certainly, the admirable goal of eliminating schistosomiasis will not be achieved unless individuals with low worm burdens can be diagnosed.

Signalling pathways in schistosomes: novel targets for control interventions against schistosomiasis

Over the last decade, there has been accumulating evidence showing that signalling pathways are involved in extensive biological and physiological processes in the human blood fluke schistosomes, playing essential roles in environmental sensing, host penetration, growth, development, maturation, embryogenesis, tissue self-renewal and survival. Owing to the likelihood of resistance developing against praziquantel, the only drug currently available that is effective against all the human schistosome species, there is an urgent requirement for an alternative treatment, arguing for continuing research into novel or repurposed anti-schistosomal drugs. An increasing number of anticancer drugs are being developed which block abnormal signalling pathways, a feature that has stimulated interest in developing novel interventions against human schistosomiasis by targeting key cell signalling components. In this review, we discuss the functional characterization of signal transduction pathways in schistosomes and consider current challenges and future perspectives in this important area of research.