A highly sensitive TaqMan real-time PCR assay for early detection of Schistosoma species

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.

Low Sensitivity of Real Time PCRs Targeting Retrotransposon Sequences for the Detection of Schistosoma japonicum Complex DNA in Human Serum

While hybridization probe-based real-time PCR assays targeting highly repetitive multi-copy genome sequences for the diagnosis of S. mansoni complex or S. haematobium complex from human serum are well established, reports on the evaluation of respective assays for the identification of S. japonicum complex DNA in human serum are scarce. Here, we assessed the potential use of the retrotransposon sequences SjR2 and SjCHGCS19 from S. japonicum, S. mekongi and S. malayensis for the diagnosis of Asian Schistosoma infections. Based on available S. japonicum sequences and newly provided S. mekongi and S. malayensis sequences, hybridization probe-based real-time PCRs targeting SjR2 and SjCHGCS19 of the S. japonicum complex were designed both as consensus primer assays as well as multi-primer assays for the coverage of multiple variants of the target sequences. The assays were established using plasmids and S. mekongi DNA. While the consensus primer assays failed to detect S. mekongi DNA in human serum samples, the multi-primer assays showed positive or borderline positive results but only in 9.8% (6/61) of serum samples from patients with confirmed S. mekongi infections. Some cross-reactions with samples positive for S. mansoni or S. haematobium were observed but with the SjCHGCS19-PCR only. In spite of the low sensitivity, the presented experience may guide future evaluations of S. japonicum-complex-specific PCRs from human serum.

Spirorchiidiasis in marine turtles: the current state of knowledge

Blood flukes of the family Spirorchiidae are important disease agents in marine turtles. The family is near cosmopolitan in distribution. Twenty-nine marine species across 10 genera are currently recognized, but taxonomic problems remain and it is likely that more species will be discovered. Spirorchiids infect the circulatory system, where they and their eggs cause a range of inflammatory lesions. Infection is sometimes implicated in the death of the turtle. In some regions, prevalence in stranded turtles is close to 100%. Knowledge of life cycles, important for control and epidemiological studies, has proven elusive until recently, when the first intermediate host identifications were made. Recent molecular studies of eggs and adult worms indicate that a considerable level of intrageneric and intraspecific diversity exists. The characterization of this diversity is likely to be of importance in exploring parasite taxonomy and ecology, unravelling life cycles, identifying the differential pathogenicity of genotypes and species, and developing antemortem diagnostic tools, all of which are major priorities for future spirorchiid research. Diagnosis to date has been reliant on copromicroscopy or necropsy, which both have significant limitations. The current lack of reliable antemortem diagnostic options is a roadblock to determining the true prevalence and epidemiology of spirorchiidiasis and the development of effective treatment regimes.

Nested-PCR assay for detection of Schistosoma japonicum infection in domestic animals

BACKGROUND

Schistosomiasis japonica is a common zoonosis. Domestic animals are the primary source of infection and play an important role in disease transmission. The prevalence and infectivity of this disease in domestic animals in China have significantly decreased and, for this reason, diagnostics with a higher sensitivity have become increasingly necessary. It was reported that polymerase chain reaction (PCR)-based methods could be used to detect schistosome infection in humans and animals and presented a high sensitivity and specificity. The present study aimed to develop a PCR-based method for detection of Schistosoma japonicum infection in domestic animals.

METHODS

A specific nested-PCR assay was developed to detect S. japonicum infection in domestic animals via amplification of a 231-bp DNA fragment of retrotransposon SjR2. The developed assay was first used in sera and dry blood filter paper (DBFP) from goats and buffaloes at different time points of infection. Then, 78 DBFPs from 39 artificially-infected bovines at 14 and 28 days post-infection and 42 DBFPs from schistosome-negative bovines from the city of Huangshan in the Anhui province were used to evaluate the diagnostic validity. Furthermore, this assay was used to detect S. japonicum infection in domestic animals in Dongzhi and Wangjiang counties.

RESULTS

The expected PCR product was detected in eggs and adult worms of S. japonicum and blood samples from S. japonicum-infected goats and water buffaloes, but not from Fasciola and Haemonchus contortus worms. The nested-PCR assay could detect the target S. japonicum DNA in DBFPs from goats and buffaloes after day 3 post-infection. The sensitivity in buffaloes at 14 and 28 days post-infection was 92.30% (36/39) and 100% (39/39), respectively. The specificity was 97.60% (41/42). The positivity rates in Dongzhi and Wangjiang counties were 6.00% and 8.00% in bovines and 22.00% and 16.67% in goats, respectively. The positivity rates in goats in both counties were higher than those in bovines with a significant difference in Dongzhi County but not in Wangjiang County (P < 0.05 and P = 0.23, respectively).

CONCLUSIONS

Our results suggest that the developed nested-PCR assay may be used for the diagnosis of S. japonicum infection in domestic animals, and the control of S. japonicum infection in goats should be paid more attention.

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.

Comparative Study of the Accuracy of Different Techniques for the Laboratory Diagnosis of Schistosomiasis Mansoni in Areas of Low Endemicity in Barra Mansa City, Rio de Janeiro State, Brazil

Schistosomiasis constitutes a major public health problem, with an estimated 200 million people infected worldwide. Many areas of Brazil show low endemicity of schistosomiasis, and the current standard parasitological techniques are not sufficiently sensitive to detect the low-level helminth infections common in areas of low endemicity (ALEs). This study compared the Kato-Katz (KK); Hoffman, Pons, and Janer (HH); enzyme-linked immunosorbent assay- (ELISA-) IgG and ELISA-IgM; indirect immunofluorescence technique (IFT-IgM); and qPCR techniques for schistosomiasis detection in serum and fecal samples, using the circumoval precipitin test (COPT) as reference. An epidemiological survey was conducted in a randomized sample of residents from five neighborhoods of Barra Mansa, RJ, with 610 fecal and 612 serum samples. ELISA-IgM (21.4%) showed the highest positivity and HH and KK techniques were the least sensitive (0.8%). All techniques except qPCR-serum showed high accuracy (82–95.5%), differed significantly from COPT in positivity (P < 0.05), and showed poor agreement with COPT. Medium agreement was seen with ELISA-IgG (Kappa = 0.377) and IFA (Kappa = 0.347). Parasitological techniques showed much lower positivity rates than those by other techniques. We suggest the possibility of using a combination of laboratory tools for the diagnosis of schistosomiasis in ALEs.

Evaluation of real-time PCR assay to detect Schistosoma mansoni infections in a low endemic setting

Background

Schistosomiasis constitutes a major public health problem, and 200 million people are estimated to be infected with schistosomiasis worldwide. In Brazil, schistosomiasis has been reported in 19 states, showing areas of high and medium endemicity and a wide range of areas of low endemicity (ALE). Barra Mansa in Rio de Janeiro state has an estimated prevalence of 1%. ALE represent a new challenge for the helminth control because about 75% of infected individuals are asymptomatic and infections occur with a low parasite load (<100 eggs per gram of feces), causing a decrease in sensitivity of stool parasitological techniques, which are a reference for the laboratory diagnosis of this helminth. The objective of this study was to evaluate the performance of a TaqMan quantitative polymerase chain reaction (qPCR) technique in serum and feces DNA samples using the techniques of Kato-Katz (KK), Hoffman, Pons and Janer (HH) as references, during an epidemiological survey using fecal samples and sera from randomized residents from an ALE.

Methods

A cross-sectional study conducted from April to December 2011 using a probabilistic sampling that collected 572 fecal and serum samples. The laboratory diagnostic techniques used were: KK, HH and qPCR (feces and serum).

Results

We obtained the following results using the different diagnostic techniques: KK and HH, 0.9% (n =5); qPCR-feces, 9.6% (n =55); and qPCR-serum, 1.4% (n =8). The qPCR-feces presented the highest positivity, whereas the techniques of HH and KK were the least sensitive to detect infections (0.8%). Compared to HH and KK, qPCR-feces showed a statistically significant difference in positivity (p <0.05), although with poor agreement.

Conclusion

The positivity rate presented by the qPCR approach was far higher than that obtained by parasitological techniques. The lack of adequate surveillance in ALE of schistosomiasis indicates a high possibility of these areas being actually of medium and high endemicity. This study presents a control perspective, pointing to the possibility of using combined laboratory tools in the diagnosis of schistosomiasis in ALE.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-014-0558-4) contains supplementary material, which is available to authorized users.

Development of "-omics" research in Schistosoma spp. and -omics-based new diagnostic tools for schistosomiasis

Schistosomiasis, caused by dioecious flatworms in the genus Schistosoma, is torturing people from many developing countries nowadays and frequently leads to severe morbidity and mortality of the patients. Praziquantel based chemotherapy and morbidity control for this disease adopted currently necessitate viable and efficient diagnostic technologies. Fortunately, those “-omics” researches, which rely on high-throughput experimental technologies to produce massive amounts of informative data, have substantially contributed to the exploitation and innovation of diagnostic tools of schistosomiasis. In its first section, this review provides a concise conclusion on the progresses pertaining to schistosomal “-omics” researches to date, followed by a comprehensive section on the diagnostic methods of schistosomiasis, especially those innovative ones based on the detection of antibodies, antigens, nucleic acids, and metabolites with a focus on those achievements inspired by “-omics” researches. Finally, suggestions about the design of future diagnostic tools of schistosomiasis are proposed, in order to better harness those data produced by “-omics” studies.

Detection of Schistosoma mansoni infection by TaqMan® Real-Time PCR in a hamster model

An experimental study in hamsters was performed to evaluate the capability for detecting Schistosoma mansoni DNA in serum and fecal samples during the pre and post-egg-laying periods of infection using TaqMan® Real-Time PCR system (qPCR), was compared with the circumoval precipitin test (COPT) and the Kato-Katz technique, especially among individuals with low parasitic burden. Twenty-four hamsters were infected with cercariae. Three hamsters were sacrificed per week under anesthesia, from 7 days post infection (DPI) up to 56 DPI. A serum sample and a pool of feces were collected from each hamster. The presence of S. mansoni eggs in fecal samples was evaluated by Kato-Katz method and in the hamsters gutby histopathology. Detection of S. mansoni DNA was performed using qPCR and S. mansoni antibody using COPT. The first detection of eggs in feces by Kato-Katz method and S. mansoni DNA in feces by qPCR occurred 49 DPI. Nevertheless, S. mansoni DNA was detected in serum samples from 14 up to 56 DPI. COPT was positive at 35 DPI. The results not only confirm the reliability of S. mansoni DNA detection by qPCR, but also demonstrate that serum is a trustworthy source of DNA in the pre patent infection period.

Diagnostic performance of Schistosoma real-time PCR in urine samples from Kenyan children infected with Schistosoma haematobium: day-to-day variation and follow-up after praziquantel treatment

Background

In an effort to enhance accuracy of diagnosis of Schistosoma haematobium, this study explores day-to-day variability and diagnostic performance of real-time PCR for detection and quantification of Schistosoma DNA compared to other diagnostic tools in an endemic area before and after treatment.

Methodology

Previously collected urine samples (N = 390) from 114 preselected proven parasitological and/or clinical S. haematobium positive Kenyan schoolchildren were analyzed by a Schistosoma internal transcribed spacer-based real-time PCR after 14 years of storage. Pre-treatment day-to-day fluctuations of PCR and microscopy over three consecutive days were measured for 24 children using intra-class correlation coefficient. A combined ‘gold standard’ (PCR and/or microscopy positive) was used to measure sensitivity and negative predictive value (NPV) of several diagnostic tools at baseline, two and 18 months post-treatment with praziquantel.

Principal Findings

All 24 repeatedly tested children were PCR-positive over three days with little daily variation in median Ct-values, while 83.3% were found to be egg-positive for S. haematobium at day 1 and 75.0% at day 2 and 3 pre-treatment, signifying daily fluctuations in microscopy diagnosis. Of all 114 preselected schoolchildren, repeated microscopic measurements were required to detect 96.5% versus 100% of positive pre-treatment cases by single PCR. At two months post-treatment, microscopy and PCR detected 22.8% versus 69.3% positive children, respectively. Based on the ‘gold standard’, PCR showed high sensitivity (>92%) as compared to >31% sensitivity for microscopy, both pre- and post-treatment.

Conclusions/Significance

Detection and quantification of Schistosoma DNA in urine by real-time PCR was shown to be a powerful and specific diagnostic tool for detection of S. haematobium infections, with less day-to-day variation and higher sensitivity compared to microscopy. The superior performance of PCR before, and two and 18 months post-treatment provides a compelling argument for PCR as an accurate and reproducible tool for monitoring treatment efficacy.

Schistosoma haematobium is a blood fluke that causes severe urogenital pathology and affects millions of people, mainly in sub-Sahara Africa. Current diagnosis is based on microscopic examination of urine samples, but this method is not only observer dependent, but also known for its low sensitivity and high day-to-day variability. Accurate diagnosis is important to assess community levels of infections for consideration of deworming campaigns, and to monitor treatment efficacy. We evaluated a real-time polymerase chain reaction (PCR) assay for specific detection and quantification of Schistosoma DNA in urine samples from 114 preselected S. haematobium infected schoolchildren of endemic coastal Kenya and compared the outcome to several other diagnostic methods. Three urine samples collected over three subsequent days from 24 participants were used for Analyzing day-to-day fluctuations in egg counts and Schistosoma DNA levels. Urine was also tested two and 18 months after praziquantel treatment. Compared to microscopy, we observed less day-to-day fluctuations and higher sensitivity with real-time PCR, in particular when tested two months after therapy. Real-time PCR is therefore useful for more accurate identification of S. haematobium, especially in monitoring control interventions.

Retrotransposon OV-RTE-1 from the carcinogenic liver fluke Opisthorchis viverrini: potential target for DNA-based diagnosis

Infections by the fish-borne liver flukes Opisthorchis viverrini and Clonorchis sinensis can lead to bile duct cancer. These neglected tropical disease pathogens occur in East Asia, with O. viverrini primarily in Thailand and Laos and C. sinensis in Cambodia, Vietnam, and China. Genomic information about these pathogens holds the potential to improve disease treatment and control. Transcriptome analysis indicates that mobile genetic elements are active in O. viverrini, including a novel non-Long Terminal Repeat (LTR) retrotransposon. A consensus sequence of this element, termed OV-RTE-1, was assembled from expressed sequence tags and PCR amplified genomic DNA. OV-RTE-1 was 3330 bp in length, encoded 1101 amino acid residues and exhibited hallmark structures and sequences of non-LTR retrotransposons including a single open reading frame encoding apurinic-apyrimidinic endonuclease (EN) and reverse transcriptase (RT). Phylogenetic analyses confirmed that OV-RTE-1 was member of the RTE clade of non-LTR retrotransposons. OV-RTE-1 is the first non-LTR retrotransposon characterized from the trematode family Opisthorchiidae. Sequences of OV-RTE-1 were targeted to develop a diagnostic tool for detection of infection by O. viverrini. PCR specific primers for detection of O. viverrini DNA showed 100% specificity and sensitivity for detection of as little as 5 fg of O. viverrini DNA whereas the PCR based approach showed 62% sensitivity and 100% specificity with clinical stool samples. The OV-RTE-1 specific PCR could be developed as a molecular diagnostic for Opisthorchis infection targeting parasite eggs in stool samples, especially in regions of mixed infection of O. viverrini and/or C. sinensis and minute intestinal flukes.

Molecular differentiation of Schistosoma japonicum and Schistosoma mekongi by real-time PCR with high resolution melting analysis

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

Application of an immunomagnetic bead ELISA based on IgY for detection of circulating antigen in urine of mice infected with Schistosoma japonicum

Schistosomiasis is an important zoonosis and some livestock especially bovine and swine play a crucial role on the disease transmission in endemic areas. The gold standard for animal Schistosoma japonicum infection is fecal examination although indirect agglutination assay (IHA) is so far mostly used in field survey and laboratory examination. Lack of sensitivity, poor practicality and high false positivity limit the use of those methods for routine veterinary detection as well as human diagnosis. A novel immunomagnetic bead ELISA based on IgY (egg yolk immunoglobulin) was developed for detection of circulating schistosomal antigen (CSA) in sera of hosts infected with S. japonicum. To assess the application of this method for diagnosis of domestic animal schistosomiasis with urine sample, the immunomagnetic bead ELISA based on IgY (IgY-IMB-ELISA) was employed in the present study to detect CSA in urine of murine schistosomiasis with either light (10 S. japonicum cercariae infection per mouse) or heavy infection (30 S. japonicum cercariae infection per mouse). The results showed that the CSA levels in urine of heavily and lightly infected mice reached a peak in 8 and 10 weeks after infection, respectively, remaining at a constant plateau in both groups by the end of the experiment (14 weeks after infection). The CSA level in urine of heavily infected mice was much higher than that of lightly infected mice from 8 to 14 weeks after infection. The effect of praziquantel treatment on the CSA level in urine of heavily infected mice was also investigated. It was found that the CSA level in urine of heavily infected mice with treatment was much lower than that of untreated mice at 4 weeks post-treatment, although still higher than that of control mice, and then gradually descended to the background level by 8 weeks after treatment. Our findings suggested that the IgY-IMB-ELISA may be an efficient and practical tool in non-invasive diagnosis of schistosome infection based on antigen detection, and evaluation of the efficacy of chemotherapy as well.