Real-time PCR demonstrates high prevalence of Schistosoma japonicum in the Philippines: implications for surveillance and 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 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.

Molecular diagnosis of urogenital schistosomiasis in pre-school children, school-aged children and women of reproductive age at community level in central Senegal

BACKGROUND

Urogenital schistosomiasis is a major public health concern in sub-Saharan Africa. In Senegal, the disease is endemic in all regions of the country. Recently, WHO strongly recommended including pre-school children and women of reproductive age during a mass drug administration campaign. It is important to describe the burden of the disease in these group at risk using innovative diagnostic tools. This study aimed to assess the use of real-time PCR in the detection of schistosomiasis cases at the community level in a seasonal transmission area.

METHODS

A cross-sectional survey was carried out in Niakhar located in the centre of Senegal. Pre-schoolchildren, school-aged children and female adolescents and adults were invited to participate in the study in April 2018. Urine samples were collected and examined using Hemastix reagent strips, filtration technique and real-time PCR. Schistosoma haematobium was detected, identified by targeting the Dra1 gene. The prevalence of urogenital schistosomiasis was determined for each group and the performance of the real-time PCR was compared with the conventional techniques.

RESULTS

A total of 428 participants were enrolled in this study including 87 (20.4%) pre-school children (1-5 years), 262 (61.3%) school-aged children between (5-14 years), 17 (3.9%) adolescents (15-17 years) and 62 (14.4%) female adults. The comparison of the diagnostic techniques has shown that the prevalence of urogenital schistosomiasis is higher using molecular technique (34.6%) compared to microscopy (20.3%). The percentage rate of haematuria using Hemastix was 23.1%. School-aged children between 5 and 14 years old were the most affected with 29.0% and 43.1% under microscopy and RT-PCR, respectively. In female participants, microscopic prevalence decreases with age, from 21.4% in school-aged children to 17.6% in adolescents and 9.7% in adults. There was good correlation between the number of eggs per 10 ml and the cycle threshold range.

CONCLUSION

These results show the importance of using molecular tools in the surveillance of schistosomiasis particularly in pre-school children and women of reproductive age.

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.

High prevalence of soil-transmitted helminth infections in Myanmar schoolchildren

Background

Achieving the elimination of soil-transmitted helminth (STH) infections requires a sufficient understanding of the current epidemiological status of STH endemicity. We aimed to examine the status of STH in Myanmar – a country with the eighth highest STH prevalence in the world, 10 years after instigation of the national deworming programme.

Methods

In August 2016 we screened for STH infections using Kato Katz (KK) microscopy and real-time PCR (qPCR) in schoolchildren from the Bago Region township of Phyu, a STH sentinel site in Myanmar. Ten schools were randomly selected, and one stool sample each from a total of 264 students was examined. Prevalence and intensity of infection were calculated for each STH.

Results

High prevalence of STH was identified in the study area with 78.8% of the schoolchildren infected with at least one STH by qPCR, and 33.3% by KK. The most prevalent STH was Trichuris trichiura, diagnosed by both KK (26.1%) and qPCR (67.1%), followed by Ascaris lumbricoides (15.5% KK; 54.9% qPCR). No hookworm infections were identified by KK; however, the qPCR analysis showed a high prevalence of Ancylostoma sp. infection (29.6%) with few Necator americanus (1.1%) infections.

Conclusions

Despite bi-annual deworming of schoolchildren in the fourth-grade and below, STH prevalence remains stubbornly high. These results informed the expansion of the Myanmar National STH control programme to include all school-aged children by the Ministry of Health and Sports in 2017, however further expansion to the whole community should be considered along with improving sanitation and hygiene measures. This would be augmented by rigorous monitoring and evaluation, including national prevalence surveys.

Molecular Techniques as Alternatives of Diagnostic Tools in China as Schistosomiasis Moving towards Elimination

Schistosomiasis japonica caused by the trematode flukes of Schistosoma japonicum was one of the most grievous infectious diseases in China in the mid-20th century, while its elimination has been placed on the agenda of the national strategic plan of healthy China 2030 after 70 years of continuous control campaigns. Diagnostic tools play a pivotal role in warfare against schistosomiasis but must adapt to the endemic status and objectives of activities. With the decrease of prevalence and infection intensity of schistosomiasis in human beings and livestock, optimal methodologies with high sensitivity and absolute specificity are needed for the detection of asymptomatic cases or light infections, as well as disease surveillance to verify elimination. In comparison with the parasitological methods with relatively low sensitivity and serological techniques lacking specificity, which both had been widely used in previous control stages, the molecular detection methods based on the amplification of promising genes of the schistosome genome may pick up the baton to assist the eventual aim of elimination. In this article, we reviewed the developed molecular methods for detecting S. japonicum infection and their application in schistosomiasis japonica diagnosis. Concurrently, we also analyzed the chances and challenges of molecular tools to the field application process in China.

The status of schistosomiasis japonica control in the Philippines: The need for an integrated approach to address a multidimensional problem

Schistosomiasis japonica remains a public health concern in many areas of the Philippines. Adequate and updated information is essential to enhance policy and service delivery toward control and elimination. Despite the efforts on schistosomiasis control in the Philippines, some challenges remain in these dimensions. An integrated surveillance system is recommended to determine the prevalence of infection in humans, animal reservoirs, and snail intermediate hosts, allowing the identification of high-priority areas for targeted interventions. This will entail the enhancement of laboratory diagnosis capacity through the use of more sensitive techniques, complemented by capacity building of concerned human and animal health professionals. Given the zoonotic nature of schistosomiasis japonica, adopting the One Health approach is essential to influence policies and interventions that may accelerate control and elimination. This can be achieved through the attainment of mass drug administration coverage targets and intensified case finding and management, robust implementation and integration of veterinary public health activities, the conduct of snail control measures, provision of safe water, sanitation, and hygiene services, and health promotion and education into the national schistosomiasis control and elimination program. This review aimed to describe the status of schistosomiasis japonica control in the Philippines in the context of human health, animal health, vector ecology and management, environmental health, and sociocultural dimensions.

Schistosomiasis in the People's Republic of China - down but not out

Schistosomiasis has been subjected to extensive control efforts in the People's Republic of China (China) which aims to eliminate the disease by 2030. We describe baseline results of a longitudinal cohort study undertaken in the Dongting and Poyang lakes areas of central China designed to determine the prevalence of Schistosoma japonicum in humans, animals (goats and bovines) and Oncomelania snails utilizing molecular diagnostics procedures. Data from the Chinese National Schistosomiasis Control Programme (CNSCP) were compared with the molecular results obtained.Sixteen villages from Hunan and Jiangxi provinces were surveyed; animals were only found in Hunan. The prevalence of schistosomiasis in humans was 1.8% in Jiangxi and 8.0% in Hunan determined by real-time polymerase chain reaction (PCR), while 18.3% of animals were positive by digital droplet PCR. The CNSCP data indicated that all villages harboured S. japonicum-infected individuals, detected serologically by indirect haemagglutination assay (IHA), but very few, if any, of these were subsequently positive by Kato-Katz (KK).Based on the outcome of the IHA and KK results, the CNSCP incorporates targeted human praziquantel chemotherapy but this approach can miss some infections as evidenced by the results reported here. Sensitive molecular diagnostics can play a key role in the elimination of schistosomiasis in China and inform control measures allowing for a more systematic approach to treatment.

Meta-analysis of variable-temperature PCR technique performance for diagnosising Schistosoma japonicum infections in humans in endemic areas

BACKGROUND

As China is moving onto schistosomiasis elimination/eradication, diagnostic methods with both high sensitivity and specificity for Schistosoma japonicum infections in humans are urgently needed. Microscopic identification of eggs in stool is proven to have poor sensitivity in low endemic regions, and antibody tests are unable to distinguish between current and previous infections. Polymerase chain reaction (PCR) technologies for the detection of parasite DNA have been theoretically assumed to show high diagnostic sensitivity and specificity. However, the reported performance of PCR for detecting S. japonicum infection varied greatly among studies. Therefore, we performed a meta-analysis to evaluate the overall diagnostic performance of variable-temperature PCR technologies, based on stool or blood, for detecting S. japonicum infections in humans from endemic areas.

METHODS

We searched literatures in eight electronic databases, published up to 20 January 2021. The heterogeneity and publication bias of included studies were assessed statistically. The risk of bias and applicability of each eligible study were assessed using the Quality Assessment of Diagnostic Accuracy Studies 2 tool (QUADAS-2). The bivariate mixed-effects model was applied to obtain the summary estimates of diagnostic performance. The hierarchical summary receiver operating characteristic (HSROC) curve was applied to visually display the results. Subgroup analyses and multivariate regression were performed to explore the source of heterogeneity. This research was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines and was registered prospectively in PROSPERO (CRD42021233165).

RESULTS

A total of 2791 papers were retrieved. After assessing for duplications and eligilibity a total of thirteen publications were retained for inclusion. These included eligible data from 4268 participants across sixteen studies. High heterogeneity existed among studies, but no publication bias was found. The pooled analyses of PCR data from all included studies resulted in a sensitivity of 0.91 (95% CI: 0.83 to 0.96), specificity of 0.85 (95% CI: 0.65 to 0.94), positive likelihood ratio of 5.90 (95% CI: 2.40 to 14.60), negative likelihood ratio of 0.10 (95% CI: 0.05 to 0.20) and a diagnostics odds ratio of 58 (95% CI: 19 to 179). Case-control studies showed significantly better performances for PCR diagnostics than cross-sectional studies. This was further evidenced by multivariate analyses. The four types of PCR approaches identified (conventional PCR, qPCR, Droplet digital PCR and nested PCR) differed significantly, with nested PCRs showing the best performance.

CONCLUSIONS

Variable-temperature PCR has a satisfactory performance for diagnosing S. japonicum infections in humans in endemic areas. More high quality studies on S. japonicum diagnostic techniques, especially in low endemic areas and for the detection of dual-sex and single-sex infections are required. These will likely need to optimise a nested PCR alongside a highly sensitive gene target. They will contribute to successfully monitoring endemic areas as they move towards the WHO 2030 targets, as well as ultimately helping areas to achieve these goals.

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.

Development of a Recombinase Polymerase Amplification Assay for Schistosomiasis Japonica Diagnosis in the Experimental Mice and Domestic Goats

Although the prevalence of schistosomiasis japonica has declined gradually in China, more accurate and sensitive diagnostic methods are urgently needed for the prevention and control of this disease. Molecular diagnostic methods are advantageous in terms of sensitivity and specificity, but they are time-consuming and require expensive instruments and skilled personnel, which limits their application in low-resource settings. In this study, an isothermal DNA amplification assay and recombinase polymerase amplification (RPA) combined with lateral flow dipstick (LFD) were set up. It was used to detect S. japonicum infections in experimental mice and domestic goats by amplifying a specific DNA fragment of S. japonicum. The lower limit of detection for the LFD-RPA assay was evaluated using dilutions of plasmid containing the target sequence. Cross-reactivity was evaluated using genomic DNA from eight other parasites. The effectiveness of the LFD-RPA assay was verified by assessing 36 positive plasma samples and 36 negative plasma samples from mice. The LFD-RPA assay and real-time PCR were also used to assess 48 schistosomiasis japonica-positive plasma samples and 53 negative plasma samples from goats. The LFD-RPA assay could detect 2.6 femtogram (fg) of S. japonicum target DNA (~39 fg genomic DNA of S. japonicum), only 10-fold less sensitive than real-time PCR assay. There was no cross-reactivity with DNA from the other eight parasites, such as Haemonchus contortus and Spirometra. The whole amplification process could be completed within 15 min at 39°C, and the results can be observed easily using the LFD. The sensitivity and specificity of the LFD-RPA assay were 97.22% (35/36, 95% CI, 85.47%-99.93%) and 100% (36/36, 95% CI, 90.26%-100%) in mice, and 93.75% (45/48, 95% CI, 82.80%-98.69%) and 100% (53/53, 95% CI, 93.28%-100%) in goats. By comparison, the sensitivity and specificity of real-time PCR were 100% (36/36, 95% CI, 90.26%-100%) and 100% (36/36, 95% CI, 90.26%-100%) for mice, and 97.92% (47/48, 95% CI, 88.93%-99.95%) and 100% (53/53, 95% CI, 93.28%-100%) for goats. The LFD-RPA assay exhibits high sensitivity and specificity for the diagnosis of schistosomiasis japonica, and it is an alternative method for diagnosis schistosomiasis japonica in low resource setting.

Development of a novel real-time polymerase chain reaction assay for the sensitive detection of Schistosoma japonicum in human stool

BACKGROUND

Elimination and control of Schistosoma japonicum, the most virulent of the schistosomiasis-causing blood flukes, requires the development of sensitive and specific diagnostic tools capable of providing an accurate measurement of the infection prevalence in endemic areas. Typically, detection of S. japonicum has occurred using the Kato-Katz technique, but this methodology, which requires skilled microscopists, has been shown to radically underestimate levels of infection. With the ever-improving capabilities of next-generation sequencing and bioinformatic analysis tools, identification of satellite sequences and other highly repetitive genomic elements for use as real-time PCR diagnostic targets is becoming increasingly common. Assays developed using these targets have the ability to improve the sensitivity and specificity of results for epidemiological studies that can in turn be used to inform mass drug administration and programmatic decision making.

METHODOLOGY/PRINCIPAL FINDINGS

Utilizing Tandem Repeat Analyzer (TAREAN) and RepeatExplorer2, a cluster-based analysis of the S. japonicum genome was performed and a tandemly arranged genomic repeat, which we named SjTR1 (Schistosoma japonicum Tandem Repeat 1), was selected as the target for a real-time PCR diagnostic assay. Based on these analyses, a primer/probe set was designed and the assay was optimized. The resulting real-time PCR test was shown to reliably detect as little as 200 ag of S. japonicum genomic DNA and as little as 1 egg per gram of human stool. Based on these results, the index assay reported in this manuscript is more sensitive than previously published real-time PCR assays for the detection of S. japonicum.

CONCLUSIONS/SIGNIFICANCE

The extremely sensitive and specific diagnostic assay described in this manuscript will facilitate the accurate detection of S. japonicum, particularly in regions with low levels of endemicity. This assay will be useful in providing data to inform programmatic decision makers, aiding disease control and elimination efforts.

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.

Comparison of point-of-care test and enzyme-linked immunosorbent assay for detection of immunoglobulin G antibodies in the diagnosis of human schistosomiasis japonica

OBJECTIVE

Schistosomiasis japonica is an important helminthic disease in Asia. Sensitive and accurate diagnostic tools are indispensable for clinical diagnosis, screening infection and monitoring its control. In this study, we developed an immunochromatographic test (Sj-ICT) to detect anti-Schistosoma japonicum immunoglobulin G antibodies in human sera.

METHODS

Somatic extract from adult S. japonicum was used as an antigen. The Sj-ICT was developed and optimized as a point-of-care test. All 214 human serum samples were evaluated for diagnostic usefulness and comparison with an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The diagnostic sensitivity, specificity, positive and negative predictive values, and accuracy of the Sj-ICT were 90.8%, 87.9%, 86.4%, 91.9% and 89.3%, respectively. For ELISA the values were respectively 91.8%, 87.9%, 86.5%, 92.7% and 89.7%. The concordance between both methods was 86.4 % (Cohen's kappa value = 0.729).

CONCLUSIONS

The immunochromatographic test kit developed can support clinical diagnosis and large-scale surveys in endemic areas without requiring additional facilities or ancillary supplies.

Diagnostic test accuracy for detecting Schistosoma japonicum and S. mekongi in humans: A systematic review and meta-analysis

Background

Most of national schistosomiasis elimination programmes in Asia are relying on stool examination, particularly Kato Katz stool examination technique for regular transmission monitoring. However, the Kato-Katz technique has shown low sensitivity for the detection of light-intensity infections, and therefore highly sensitive diagnostic tools are urgently required to monitor prevalence of infection in low transmission settings. The objective of this systematic review was to evaluate and synthesize the performance of diagnostic tests for detecting Schistosoma japonicum and S. mekongi infection in people living in endemic areas.

Methodology/Principal findings

We comprehensively searched these nine electronic databases and other resources until July 2019, with no language or publication limits: PubMed, EMBASE, MEDLINE, Web of Science, BIOSIS Citation Index, HTA, CINAHL PLUS, The Cochrane Library, and PsycINFO. We included original studies that assessed diagnostic performance using antibody, antigen, and molecular tests with stool examination test as a reference standard. Two reviewers independently extracted a standard set of data and assessed study quality. We estimated the pooled estimates of sensitivity and specificity for each index test. We used diagnostic odds ratio to determine the overall accuracy and hierarchical summary receiver operating characteristics (HSROC) curve to assess the index tests performance.

Fifteen studies (S. japonicum [n = 13] and S. mekongi [n = 2]) testing 15,303 participants were included in the review. Five studies reported performance of enzyme-linked immunosorbent assay (ELISA), seven studies reported indirect hemagglutination assay (IHA), and four studies reported polymerase chain reaction (PCR) for detecting S. japonicum. The pooled sensitivity and specificity were 0.93 (95% CI: 0.84–0.98) and 0.40 (95% CI: 0.29–0.53) for ELISA, 0.97 (95% CI: 0.90–0.99) and 0.66 (95% CI: 0.58–0.73) for IHA, and 0.89 (95% CI: 0.71–0.96) and 0.49 (95% CI: 0.29–0.69) for PCR respectively. A global summary indicated the best performance for IHA, closely followed by ELISA. We were unable to perform meta-analysis for S. mekongi due to insufficient number of studies.

Conclusions/Significance

IHA showed the highest detection accuracy for S. japonicum. Further studies are needed to determine the suitable diagnostic methods to verify the absence of transmission of S. mekongi and also to compare detection accuracy against more sensitive reference standards such as PCR.

Schistosomiasis remains a serious public health problem worldwide. Accurate diagnostic tests play a key role in control of schistosomiasis, especially in Asia where the prevalence and intensity of infection is low. As stool examination techniques, particularly the Kato-Katz technique has shown low sensitivity for the detection of light-intensity infections, highly sensitive diagnostics are urgently required to monitor prevalence of infection in low transmission settings. The purpose of this review was to assess and synthesize the performance of diagnostic tests for detecting schistosomiasis in people living in endemic areas in Asia. A comprehensive search, without any limit of language, date or types of publication, were performed for both- multiple electronic databases and other resources to identify the eligible studies. Robust analytical approaches such as diagnostic meta-analysis, HSROC curve, and diagnostic odds ratio, were used to provide more diagnostic accuracy of index tests. We assessed performance of three diagnostic tests (ELISA, IHA, and PCR) for detecting infection with S. japonicum using stool examination as a reference standard. In these meta-analyses, IHA showed the highest detection accuracy, followed by ELISA. We could not perform meta-analysis for S. mekongi due to insufficient number of studies.

Rapid parasite detection utilizing a DNA dipstick

Molecular diagnostics are powerful tools for disease detection but are typically confined to the laboratory environment due to the cumbersome methods required to extract nucleic acids from biological samples. Accurate diagnosis is essential for early detection of parasitic worm infections and for monitoring control programs, particularly during new transmission outbreaks to limit infection spread. We optimized the recently developed DNA dipstick technology to purify Schistosoma japonicum DNA from different life stages in <60 s. We successfully detected DNA from adult worms, eggs and infected snails. The speed and simplicity of this method enables the point-of-care detection of S. japonicum.

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.

Molecular identification of Ancylostoma ceylanicum in the Philippines

Hookworms are some of the most widespread of the soil-transmitted helminths (STH) with an estimated 438.9 million people infected. Until relatively recently Ancylostoma ceylanicum was regarded as a rare cause of hookworm infection in humans, with little public health relevance. However, recent advances in molecular diagnostics have revealed a much higher prevalence of this zoonotic hookworm than previously thought, particularly in Asia. This study examined the prevalence of STH and A. ceylanicum in the municipalities of Palapag and Laoang in the Philippines utilizing real-time polymerase chain reaction (PCR) on stool samples previously collected as part of a cross-sectional survey of schistosomiasis japonica. Prevalence of hookworm in humans was high with 52.8% (n = 228/432) individuals positive for any hookworm, 34.5% (n = 149/432) infected with Necator americanus, and 29.6% (n = 128/432) with Ancylostoma spp; of these, 34 were PCR-positive for A. ceylanicum. Considering dogs, 12 (n = 33) were PCR-positive for A. ceylanicum. This is the first study to utilize molecular diagnostics to identify A. ceylanicum in the Philippines with both humans and dogs infected. Control and elimination of this zoonotic hookworm will require a multifaceted approach including chemotherapy of humans, identification of animal reservoirs, improvements in health infrastructure, and health education to help prevent infection.

Granuloma formation and tissue pathology in Schistosoma japonicum versus Schistosoma mansoni infections

Schistosomiasis is the most important helminth disease in the world from a public health perspective. S mansoni and S japonicum account for the majority of global intestinal schistosomiasis cases, and the pathogenesis is widely assumed to be fundamentally similar. However, the majority of research on schistosomiasis has been carried out on S mansoni and comparisons between the two species are rarely made. Here, we will discuss aspects of both older and recent literature where such comparisons have been made, with a particular focus on the pathological agent, the host granulomatous response to the egg. Major differences between the two species are apparent in features such as egg production patterns and cellular infiltration; however, it is also clear that even subtle differences in the cascade of various cytokines and chemokines contribute to the different levels of pathology observed between these two main species of intestinal schistosomiasis. A better understanding of such differences at species level will be vital when it comes to the development of new treatment strategies and vaccines.

Accuracy of real-time polymerase chain reaction to detect Schistosoma mansoni - infected individuals from an endemic area with low parasite loads

Due to the efforts to control schistosomiasis transmission in tropical countries, a large proportion of individuals from endemic areas present low parasite loads, which hinders diagnosis of intestinal schistosomiasis by the Kato-Katz (KK) method. Therefore, the development of more sensitive diagnostic methods is essential for efficient control measures. The aim was to evaluate the accuracy of a real-time polymerase chain reaction (RT-PCR) to detect Schistosoma mansoni DNA in fecal samples of individuals with low parasite loads. A cross-sectional population-based study was conducted in a rural community (n = 257) in Brazil. POC-CCA® was performed in urine and feces were used for RT-PCR. In addition, fecal exams were completed by 18 KK slides, saline gradient and Helmintex techniques. The combined results of the three parasitological tests detected schistosome eggs in 118 participants (45.9%) and composed the consolidated reference standard (CRS). By RT-PCR, 117 out of 215 tested samples were positive, showing 91.4% sensitivity, 80.2% specificity and good concordance with the CRS (kappa = 0.71). RT-PCR identified 86.9% of the individuals eliminating less than 12 eggs/g of feces, demonstrating much better performance than POC-CCA® (50.8%). Our results showed that RT-PCR is a valuable alternative for the diagnosis of intestinal schistosomiasis in individuals with very low parasite loads.

Helminths, polyparasitism, and the gut microbiome in the Philippines

Polyparasitism, involving soil-transmitted helminths. and Schistosoma blood flukes, is common in low to middle income countries. These helminths impact on the gut environment and can cause changes to the gut microbiome composition. Here we examined the gut microbiome in individuals with polyparasitism from two human cohorts in the Philippines utilising DNA sequencing-based profiling. Multiple helminth species infections were high with 70.3% of study participants harbouring at least two parasite species, and 16% harbouring at least five species. Increased numbers of helminth co-infections, in particular with the gut-resident soil-transmitted helminths, were significantly associated with increased bacterial diversity; however no significant parasite-gut microbiome associations were evident for individuals infected only with Schistosoma japonicum. In general, a healthy gut is associated with high bacterial diversity, which in these human cohorts may be the result of helminth-mediated immune modulation, or due to changes in the gut environment caused by these parasitic helminths.

Persistence of Schistosoma japonicum DNA in a Kidney-Liver Transplant Recipient

Mitochondrial genome analysis of Schistosoma japonicum suggests that diversity of intermediate host snails drove intra-species divergence during its expansion in Asia. We applied the knowledge of this genomic variation to study an unusual patient we recently diagnosed with schistosomiasis. The patient had not visited any schistosomiasis-endemic countries for more than 35 years and had no idea where she became infected. Unusual clinical features of this patient included the absence of egg granulomas in tissue and persistent noncalcified eggs despite multiple praziquantel (PZQ) treatments over 7 years. A digital droplet polymerase chair reaction (PCR) assay that specifically targets the schistosome 1,4 dihydronicotinamide adenine dinucleotide-1 (NADH1) dehydrogenase-1 mitochondrial gene successfully amplified parasite DNA extracted from colon biopsies. DNA sequence analysis of parasite DNA revealed that it was a Philippine strain of S. japonicum. Future molecular studies using stored DNA from patients such as this may provide new insight into why some persons do not respond well to PZQ treatment.

Currently Available Monitoring and Surveillance Systems for Taenia spp., Echinococcus spp., Schistosoma spp., and Soil-Transmitted Helminths at the Control/Elimination Stage: A Systematic Review

An increasing global focus on neglected tropical diseases (NTDs) has resulted in the set up of numerous control and elimination activities worldwide. This is partly true for Taenia solium taeniasis/cysticercosis, the most important foodborne parasitic infection. Despite substantial progress, adequate monitoring and surveillance (M&S) are required to sustain a status of control/elimination. This is often lacking, especially for T. solium. Therefore, the objective was to conduct a systematic literature review of the currently available M&S systems at the control/elimination stage of the four top-ranked helminth NTDs. Specifically, Taenia spp., Echinococcus spp., Schistosoma spp., and soil-transmitted helminths (STHs) were considered to determine if there are any similarities between their M&S systems and whether certain approaches can be adopted from each other. The systematic review demonstrated that rigorous M&S systems have been designed for the control/elimination stage of both STHs and schistosomiasis, particularly in China. On the other hand, a concept of M&S for Taenia spp. and Echinococcus spp. has not been fully developed yet, due to a lack of epidemiological data and the fact that many endemic countries are far away from reaching control/elimination. Moreover, accurate diagnostic tools for all four diseases are still imperfect, which complicates proper M&S. Finally, there is an urgent need to develop and harmonize/standardize M&S activities in order to reliably determine and compare the epidemiological situation worldwide.

Collaborative RNAS+ research: Priorities and outcomes

Over the past 20 years, RNAS⁺ has been generating research results from highly collaborative projects meant to promote and advance understanding in various aspects of schistosomiasis. Epidemiological studies in endemic countries like the Philippines, the People's Republic of China (PR China), the Lao People's Democratic Republic (Lao PDR) and Cambodia clarified the role of reservoir hosts in transmission and the use of spatio-temporal methods such as remote sensing and geographical information systems (GIS) in surveillance of schistosomiasis. Morbidity studies proposed factors that might influence development of fibrosis, anaemia and malnutrition in schistosomiasis. Immune responses in schistosomiasis continue to be an interesting focus in research to explain possible development of resistance with age. Results of evaluation of candidate vaccine molecules are also presented. New diagnostics are continually being developed in response to the call for more sensitive and field applicable techniques that will be used for surveillance in areas nearing elimination of the disease. Several studies presented here show the insufficiency of mass drug administration (MDA) with praziquantel in eliminating the disease. Emphasis is given to an integrated control approach that can be accomplished through intensive and extensive intersectoral collaboration.

Schistosomiasis Elimination: Beginning of the End or a Continued March on a Trodden Path

In spite of spectacular progress towards the goal of elimination of schistosomiasis, particularly in China but also in other areas, research gaps and outstanding issues remain. Although expectations of achieving elimination of this disease have never been greater, all constraints have not been swept aside. Indeed, there are some formidable obstacles, such as insufficient amounts of drugs to treat everybody and still limited use of high-sensitive diagnostic techniques, both for the definitive and the intermediate hosts, which indicate that prevalence is considerably underrated in well-controlled areas. Elimination will be difficult to achieve without a broad approach, including a stronger focus on transmission, better diagnostics and the establishment of a reliable survey system activating a rapid response when called for. Importantly, awareness of the crucial importance of transmission has been revived resulting in renewed interest in snail control together with more emphasis on health education and sanitation. The papers collected in this special issue entitled ‘Prospects for Schistosomiasis Elimination’ reflect these issues and we are particularly pleased to note that some also discuss the crucial question when to declare a country free of schistosomiasis and present techniques that together create an approach that can show unequivocally when interruption of transmission has been achieved.

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.

Co-parasitism of intestinal protozoa and Schistosoma japonicum in a rural community in the Philippines

Background

Co-parasitism is a frequent occurrence in impoverished communities in the tropics resulting in a considerable disease burden. While there are extensive reports of intestinal helminthiases, including schistosomiasis japonica, the occurrence and extent of diseases caused by intestinal protozoa (IP) have yet to be investigated in depth in the Philippines. We present a detailed analysis of polyparasitism in a rural community of Northern Samar, focusing on co-infections of IP with Schistosoma japonicum.

Methods

A descriptive cross sectional study was carried out in 2015 across 18 barangays (villages) endemic for S. japonicum in Northern Samar, the Philippines to assess the burden of human schistosomiasis and IP infections. Faecal samples collected from 412 participants from the 18 barangays were included in the final molecular analysis. A multiplex quantitative PCR assay was developed and used for the detection of Blastocystis spp., Entamoeba histolytica, Cryptosporidium spp. and Giardia duodenalis in stool samples. The findings were combined with previous results of droplet digital PCR diagnosis of individuals from the same 18 barangays infected with S. japonicum determined using the same stool samples for analysis.

Results

Mean age of the study participants was 40.3 years (95% CI: 38.8–41.8) with 53% (n = 218) being males. Prevalence of S. japonicum (74.5%) and Blastocystis spp. (58.7%) was significantly higher compared to other infections, with E. histolytica having the lowest prevalence (12.1%). A majority of individuals were infected with more than one parasite with two infections being most common (n = 175, 42.5%). The prevalence of individuals with two parasites was significantly higher than all others with 27.9% (n = 115) subjects harbouring a single parasite species. Of individuals with two infections, S. japonicum and Blastocystis spp. were the most common combination (n = 110, 62.9%). Examining age within the population, 58.5% (n = 38) of school-aged children and 60.1% (n = 14) of women of child bearing age harboured at least two parasite species.

Conclusions

The study revealed that polyparasitism with IP infections and schistosomiasis japonica is highly prevalent in individuals in Northern Samar which likely contributes to the significant public health and socio-economic burden suffered by this population. More generally, the findings are of relevance when considering implementation of integrated control strategies for intestinal parasites.

Electronic supplementary material

The online version of this article (10.1186/s40249-018-0504-6) contains supplementary material, which is available to authorized users.

DNA Diagnostics for Schistosomiasis Control

Despite extensive efforts over the last few decades, the global disease burden of schistosomiasis still remains unacceptably high. This could partly be attributed to the lack of accurate diagnostic tools for detecting human and animal schistosome infections in endemic areas. In low transmission and low prevalence areas where schistosomiasis elimination is targeted, case detection requires a test that is highly sensitive. Diagnostic tests with low sensitivity will miss individuals with low infection intensity and these will continue to contribute to transmission, thereby interfering with the efficacy of the control measures operating. Of the many diagnostic approaches undertaken to date, the detection of schistosome DNA using DNA amplification techniques including polymerase chain reaction (PCR) provide valuable adjuncts to more conventional microscopic and serological methods, due their accuracy, high sensitivity, and the capacity to detect early pre-patent infections. Furthermore, DNA-based methods represent important screening tools, particularly in those endemic areas with ongoing control where infection prevalence and intensity have been reduced to very low levels. Here we review the role of DNA diagnostics in the path towards the control and elimination of schistosomiasis.

Real-time PCR diagnosis of Schistosoma japonicum in low transmission areas of China

Background

Schistosomiasis in the People’s Republic of China (PRC) can be traced back to antiquity. In the past 60 years, the Chinese government has made great efforts to control this persistent disease with elimination slated by 2020 through the implementation of a comprehensive control strategy. This strategy aims to reduce the role of bovines and humans as sources of infection as a pre-requisite for elimination through transmission interruption. The goal of elimination will be achievable only by the implementation of a sustainable surveillance and control system, with sensitive diagnosis a key feature so that the true disease burden is not underestimated. Currently used diagnostics lack the necessary sensitivity to accurately determine the prevalence of Schistosoma japonicum infection in areas with low infection intensities. It is of critical importance to find and treat people and to identify animals with low-level infections if the National Control Programme for China is to achieve schistosomiasis elimination.

Methods

We evaluated a real-time polymerase chain reaction (qPCR) assay using 633 human stool samples collected from five villages in Hunan, Anhui, Hubei, and Jiangxi provinces, and 182 bovine (70 cattle and 112 buffalo) stool samples obtained from four villages in Hunan, Anhui, and Jiangxi provinces in the PRC. All stool samples were subjected to the miracidium hatching test (MHT, a diagnostic procedure used in the National Schistosomiasis Control Programme) and the qPCR assay. Samples positive by MHT were subjected to either the Kato-Katz technique for humans, or the formalin-ethyl acetate sedimentation-digestion (FEA-SD) procedure for bovines, to determine infection intensities.

Results

The qPCR assay exhibited a high level of sensitivity in the detection of S. japonicum infections. With both the human and bovine samples, a significantly higher prevalence was determined using the qPCR assay (11.06% humans, 24.73% bovines) than with the MHT (0.93% humans, 7.69% bovines). The animal contamination index (calculated using data obtained with the qPCR technique) for all positive bovines was 27 618 000 eggs per day, indicating a considerable amount of environmental egg contamination that would be underestimated using less sensitive diagnostic procedures.

Conclusions

The qPCR assay we have evaluated will be applicable as a future field diagnostic and surveillance tool in low-transmission zones where schistosomiasis elimination is targeted and for monitoring post-intervention areas to verify that elimination has been maintained.

Electronic supplementary material

The online version of this article (10.1186/s40249-018-0390-y) contains supplementary material, which is available to authorized users.

Status of soil-transmitted helminth infections in schoolchildren in Laguna Province, the Philippines: Determined by parasitological and molecular diagnostic techniques

BACKGROUND

Soil-transmitted helminths (STH) are the most common parasitic infections in impoverished communities, particularly among children. Current STH control is through school-based mass drug administration (MDA), which in the Philippines is done twice annually. As expected, MDA has decreased the intensity and prevalence of STH over time. As a result, the common Kato Katz (KK) thick smear method of detecting STH is less effective because it lacks sensitivity in low intensity infections, making it difficult to measure the impact of deworming programs.

METHODOLOGY/PRINCIPAL FINDINGS

A cross-sectional study was carried out over a four-week period from October 27, 2014 until November 20, 2014 in Laguna province, the Philippines. Stool samples were collected from 263 schoolchildren, to determine the prevalence of STH and compare diagnostic accuracy of multiplex quantitative polymerase chain reaction (qPCR) with the KK. A large discrepancy in the prevalence between the two techniques was noted for the detection of at least one type of STH infection (33.8% by KK vs. 78.3% by qPCR), Ascaris lumbricoides (20.5% by KK vs. 60.8% by qPCR) and Trichuris trichiura (23.6% by KK vs. 38.8% by qPCR). Considering the combined results of both methods, the prevalence of at least one type of helminth infection, A. lumbricoides, and T. trichiura were 83.3%, 67.7%, and 53.6%, respectively. Sensitivity of the qPCR for detecting at least one type of STH infection, A. lumbricoides, and T. trichiura were 94.1%, 89.9%, and 72.3% respectively; whereas KK sensitivity was 40.6%, 30.3%, and 44.0%, respectively. The qPCR method also detected infections with Ancylostoma spp. (4.6%), Necator americanus (2.3%), and Strongyloides stercoralis (0.8%) that were missed by KK.

CONCLUSION/SIGNIFICANCE

qPCR may provide new and important diagnostic information to improve assessment of the effectiveness and impact of integrated control strategies particularly in areas where large-scale STH control has led to low prevalence and/or intensity of infection.

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

Schistosoma japonicum is stubbornly persistent in China and the Philippines. Fast and accurate diagnostic tools are required to monitor effective control measures against schistosomiasis japonica. Promising antigen candidates for the serological diagnosis of schistosomiasis japonica have generally been identified from the Chinese strain of S. japonicum. However, the Chinese (SjC) and Philippine (SjP) strains of S. japonicum express a number of clear phenotypic differences, including aspects of host immune responses. This feature thereby emphasized the requirement to determine whether antigens identified as having diagnostic value for SjC infection are also suitable for the diagnosis of SjP infection. In the current study, 10 antigens were selected for comparison of diagnostic performance of the SjP infection using ELISA. On testing of sera from 180 subjects in the Philippines, SjSAP4 exhibited the best diagnostic performance with 94.03% sensitivity and 98.33% specificity using an optimized serum dilution. In another large scale testing with 412 serum samples, a combination (SjSAP4 + Sj23-LHD (large hydrophilic domain)) provided the best diagnostic outcome with 87.04% sensitivity and 96.67% specificity. This combination could be used in future for serological diagnosis of schistosomiasis in the Philippines, thereby representing an important component for monitoring integrated control measures.

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Sj23-LHD was the most promising antigen candidate for early diagnosis of schistosomiasis japonica in a murine model.

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SjSAP4 + Sj23-LHD had the highest diagnostic value when probed with sera from a human cohort with low infection intensity.

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We have developed a novel diagnostic tool that can aid in the integrated control of schistosomiasis in the Philippines.

Schistosomiasis japonica remains a major public health concern in China and the Philippines. Development of accurate and affordable diagnostic tools is a necessity for the control and elimination of schistosomiasis. The differences in the mammalian host immunological responses to Chinese (SjC) and Philippine (SjP) strains of S. japonicum necessitated validation of proven SjC serological markers for application in the diagnosis of SjP infections. Ten antigens were selected for comparison, in ELISA, for their potential of the diagnosis of SjP infection. The results provide the basis for developing an affordable and easy-to-operate tool for the diagnosis of schistosomiasis in the Philippines.

Rodents, goats and dogs - their potential roles in the transmission of schistosomiasis in China

Schistosomiasis in China has been substantially reduced due to an effective control programme employing various measures including bovine and human chemotherapy, and the removal of bovines from endemic areas. To fulfil elimination targets, it will be necessary to identify other possible reservoir hosts for Schistosoma japonicum and include them in future control efforts. This study determined the infection prevalence of S. japonicum in rodents (0-9·21%), dogs (0-18·37%) and goats (6·9-46·4%) from the Dongting Lake area of Hunan province, using a combination of traditional coproparasitological techniques (miracidial hatching technique and Kato-Katz thick smear technique) and molecular methods [quantitative real-time PCR (qPCR) and droplet digital PCR (ddPCR)]. We found a much higher prevalence in goats than previously recorded in this setting. Cattle and water buffalo were also examined using the same procedures and all were found to be infected, emphasising the occurrence of active transmission. qPCR and ddPCR were much more sensitive than the coproparasitological procedures with both KK and MHT considerably underestimating the true prevalence in all animals surveyed. The high level of S. japonicum prevalence in goats indicates that they are likely important reservoirs in schistosomiasis transmission, necessitating their inclusion as targets of control, if the goal of elimination is to be achieved in China.

Sources of variability in the measurement of Ascaris lumbricoides infection intensity by Kato-Katz and qPCR

Background

Understanding and quantifying the sources and implications of error in the measurement of helminth egg intensity using Kato-Katz (KK) and the newly emerging “gold standard” quantitative polymerase chain reaction (qPCR) technique is necessary for the appropriate design of epidemiological studies, including impact assessments for deworming programs.

Methods

Repeated measurements of Ascaris lumbricoides infection intensity were made from samples collected in western Kenya using the qPCR and KK techniques. These data were combined with data on post-treatment worm expulsions. Random effects regression models were used to quantify the variability associated with different technical and biological factors for qPCR and KK diagnosis. The relative precision of these methods was compared, as was the precision of multiple qPCR replicates.

Results

For both KK and qPCR, intensity measurements were largely determined by the identity of the stool donor. Stool donor explained 92.4% of variability in qPCR measurements and 54.5% of observed measurement variance for KK. An additional 39.1% of variance in KK measurements was attributable to having expelled adult A. lumbricoides worms following anthelmintic treatment. For qPCR, the remaining 7.6% of variability was explained by the efficiency of the DNA extraction (2.4%), plate-to-plate variability (0.2%) and other residual factors (5%). Differences in replicate measurements by qPCR were comparatively small. In addition to KK variability based on stool donor infection levels, the slide reader was highly statistically significant, although it only explained 1.4% of the total variation. In a comparison of qPCR and KK variance to mean ratios under ideal conditions, the coefficient of variation was on average 3.6 times larger for KK highlighting increased precision of qPCR.

Conclusions

Person-to-person differences explain the majority of variability in egg intensity measurements by qPCR and KK, with very little additional variability explained by the technical factors associated with the practical implementation of these techniques. qPCR provides approximately 3.6 times more precision in estimating A. lumbricoides egg intensity than KK, and could potentially be made more cost-effective by testing each sample only once without diminishing the power of a study to assess population-level intensity and prevalence.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2164-y) contains supplementary material, which is available to authorized users.

A novel duplex ddPCR assay for the diagnosis of schistosomiasis japonica: proof of concept in an experimental mouse model

The current World Health Organization strategic plan targets the elimination of schistosomiasis as a public health problem by 2025 and accurate diagnostics will play a pivotal role in achieving this goal. DNA-based detection methods provide a viable alternative to some of the commonly used tests, notably microscopy and serology, for the diagnosis of schistosomiasis. The detection of parasite cell-free DNA in different clinical samples is a recent valuable advance, which provides significant benefits for accurate disease diagnosis. Here we validated a novel duplex droplet digital PCR assay for the diagnosis of Chinese (SjC) and Philippine (SjP) strains of Schistosoma japonicum infection in a mouse model. The assay proved applicable for both SjC and SjP infections and capable of detecting infection at a very early intra-mammalian stage in conveniently obtainable samples (urine and saliva) as well as in serum and feces. The target DNA copy numbers obtained in the assay showed a positive correlation with the infection burden assessed by direct traditional parasitology. The potential to detect parasite DNA in urine and saliva has important practical implications for large-scale epidemiological screening programmes in the future, particularly in terms of logistical convenience, and the assay has the potential to be a valuable additional tool for the diagnosis of schistosomiasis japonica.

Nucleic acid detection in the diagnosis and prevention of schistosomiasis

Schistosomiasis is an important zoonotic parasitic disease that causes serious harms to humans and animals. Surveillance and diagnosis play key roles in schistosomiasis control, however, current techniques for surveillance and diagnosis of the disease have limitations. As genome data for parasites are increasing, novel techniques for detection incorporating nucleotide sequences are receiving widespread attention. These sensitive, specific, and rapid detection methods are particularly important in the diagnosis of low-grade and early infections, and may prove to have clinical significance. This paper reviews the progress of nucleic acid detection in the diagnosis and prevention of schistosomiasis, including such aspects as the selection of target genes, and development and application of nucleic acid detection methods.

Optimisation of a droplet digital PCR assay for the diagnosis of Schistosoma japonicum infection: A duplex approach with DNA binding dye chemistry

Schistosomiasis is a chronically debilitating helminth infection with a significant socio-economic and public health impact. Accurate diagnostics play a pivotal role in achieving current schistosomiasis control and elimination goals. However, many of the current diagnostic procedures, which rely on detection of schistosome eggs, have major limitations including lack of accuracy and the inability to detect pre-patent infections. DNA-based detection methods provide a viable alternative to the current tests commonly used for schistosomiasis diagnosis. Here we describe the optimisation of a novel droplet digital PCR (ddPCR) duplex assay for the diagnosis of Schistosoma japonicum infection which provides improved detection sensitivity and specificity. The assay involves the amplification of two specific and abundant target gene sequences in S. japonicum; a retrotransposon (SjR2) and a portion of a mitochondrial gene (nad1). The assay detected target sequences in different sources of schistosome DNA isolated from adult worms, schistosomules and eggs, and exhibits a high level of specificity, thereby representing an ideal tool for the detection of low levels of parasite DNA in different clinical samples including parasite cell free DNA in the host circulation and other bodily fluids. Moreover, being quantitative, the assay can be used to determine parasite infection intensity and, could provide an important tool for the detection of low intensity infections in low prevalence schistosomiasis-endemic areas.

Cell-Free DNA as a Diagnostic Tool for Human Parasitic Infections

Parasites often cause devastating diseases and represent a significant public health and economic burden. More accurate and convenient diagnostic tools are needed in support of parasite control programmes in endemic regions, and for rapid point-of-care diagnosis in nonendemic areas. The detection of cell-free DNA (cfDNA) is a relatively new concept that is being applied in the current armamentarium of diagnostics. Here, we review the application of cfDNA detection with nucleic acid amplification tests for the diagnosis and evaluation of different human parasitic infections and highlight the significant benefits of the approach using non-invasive clinical samples.

National survey data for zoonotic schistosomiasis in the Philippines grossly underestimates the true burden of disease within endemic zones: implications for future control

Zoonotic schistosomiasis has a long endemic history in the Philippines. Human mass drug administration has been the cornerstone of schistosomiasis control in the country for the past three decades. Recent publications utilizing retrospective national survey data have indicated that the national human prevalence of the disease is <1%, hence the disease is now close to elimination. However, the evidence for such a claim is weak, given that less than a third of the human population is currently being treated annually within endemic zones and only a third of those treated actually swallow the tablets. For those who consume the drug at the single oral dose of 40mg/kg, the estimated cure rate is 52% based on a recent meta-analysis. Thus, approximately 5% of the endemic human population is in reality receiving the appropriate treatment. To compound this public health problem, most of the bovines in the endemic communities are concurrently infected but are not treated under the current national control programme. Given this evidence, it is believed that the human prevalence of schistosomiasis within endemic regions has been grossly underestimated. Inherent flaws in the reporting of national schistosomiasis prevalence data are reported here, and the problems of utilizing national retrospective data in making geographic information system (GIS) risk maps and advising policy makers of the outcomes are highlighted.

Is PCR the Next Reference Standard for the Diagnosis of Schistosoma in Stool? A Comparison with Microscopy in Senegal and Kenya

BACKGROUND

The current reference test for the detection of S. mansoni in endemic areas is stool microscopy based on one or more Kato-Katz stool smears. However, stool microscopy has several shortcomings that greatly affect the efficacy of current schistosomiasis control programs. A highly specific multiplex real-time polymerase chain reaction (PCR) targeting the Schistosoma internal transcriber-spacer-2 sequence (ITS2) was developed by our group a few years ago, but so far this PCR has been applied mostly on urine samples. Here, we performed more in-depth evaluation of the ITS2 PCR as an alternative method to standard microscopy for the detection and quantification of Schistosoma spp. in stool samples.

METHODOLOGY/PRINCIPAL FINDINGS

Microscopy and PCR were performed in a Senegalese community (n = 197) in an area with high S. mansoni transmission and co-occurrence of S. haematobium, and in Kenyan schoolchildren (n = 760) from an area with comparatively low S. mansoni transmission. Despite the differences in Schistosoma endemicity the PCR performed very similarly in both areas; 13-15% more infections were detected by PCR when comparing to microscopy of a single stool sample. Even when 2-3 stool samples were used for microscopy, PCR on one stool sample detected more infections, especially in people with light-intensity infections and in children from low-risk schools. The low prevalence of soil-transmitted helminthiasis in both populations was confirmed by an additional multiplex PCR.

CONCLUSIONS/SIGNIFICANCE

The ITS2-based PCR was more sensitive than standard microscopy in detecting Schistosoma spp. This would be particularly useful for S. mansoni detection in low transmission areas, and post-control settings, and as such improve schistosomiasis control programs, epidemiological research, and quality control of microscopy. Moreover, it can be complemented with other (multiplex real-time) PCRs to detect a wider range of helminths and thus enhance effectiveness of current integrated control and elimination strategies for neglected tropical diseases.

Multiplex real-time PCR monitoring of intestinal helminths in humans reveals widespread polyparasitism in Northern Samar, the Philippines

The global socioeconomic importance of helminth parasitic disease is underpinned by the considerable clinical impact on millions of people. While helminth polyparasitism is considered common in the Philippines, little has been done to survey its extent in endemic communities. High morphological similarity of eggs between related species complicates conventional microscopic diagnostic methods which are known to lack sensitivity, particularly in low intensity infections. Multiplex quantitative PCR diagnostic methods can provide rapid, simultaneous identification of multiple helminth species from a single stool sample. We describe a multiplex assay for the differentiation of Ascaris lumbricoides, Necator americanus, Ancylostoma, Taenia saginata and Taenia solium, building on our previously published findings for Schistosoma japonicum. Of 545 human faecal samples examined, 46.6% were positive for at least three different parasite species. High prevalences of S. japonicum (90.64%), A. lumbricoides (58.17%), T. saginata (42.57%) and A. duodenale (48.07%) were recorded. Neither T. solium nor N. americanus were found to be present. The utility of molecular diagnostic methods for monitoring helminth parasite prevalence provides new information on the extent of polyparasitism in the Philippines municipality of Palapag. These methods and findings have potential global implications for the monitoring of neglected tropical diseases and control measures.

New diagnostic tools in schistosomiasis

Schistosomiasis is a water-based parasitic disease that affects over 250 million people. Control efforts have long been in vain, which is one reason why schistosomiasis is considered a neglected tropical disease. However, since the new millennium, interventions against schistosomiasis are escalating. The initial impetus stems from a 2001 World Health Assembly resolution, urging member states to scale-up deworming of school-aged children with the anthelminthic drug praziquantel. Because praziquantel is safe, efficacious and inexpensive when delivered through the school platform, diagnosis before drug intervention was deemed unnecessary and not cost-effective. Hence, there was little interest in research and development of novel diagnostic tools. With the recent publication of the World Health Organization (WHO) Roadmap to overcome the impact of neglected tropical diseases in 2020, we have entered a new era. Elimination of schistosomiasis has become the buzzword and this has important ramifications for diagnostic tools. Indeed, measuring progress towards the WHO Roadmap and whether local elimination has been achieved requires highly accurate diagnostic assays. Here, we introduce target product profiles for diagnostic tools that are required for different stages of a schistosomiasis control programme. We provide an update of the latest developments in schistosomiasis diagnosis, including microscopic techniques, rapid diagnostic tests for antigen detection, polymerase chain reaction (PCR) assays and proxy markers for morbidity assessments. Particular emphasis is placed on challenges and solutions for new technologies to enter clinical practice.