Copro-PCR based detection of Schistosoma eggs using mitochondrial DNA markers

A Novel PCR-RFLP to Detect and Differentiate Schistosoma spindale and S. indicum, the Pathogenic Schistosomes in Indian Cattle

PURPOSE

Visceral schistosomosis is an economically important trematode infection caused by Schistosoma spindale and S. indicum in among ruminants. The lack of sensitive diagnostic tools has often led to underestimation of the prevalence in live animals. A sensitive copro-PCR targeting partial mitochondrial gene was developed to detect Schistosoma spp. However, this protocol could not differentiate between the two species. This study was conducted to explore the possibility of species differentiation using restriction fragment length polymorphism of PCR products (PCR- RFLP).

METHODS

Polymerase chain reaction was carried out to amplify mitochondrial gene of adult S. spindale and S. indicum. Copro PCR was done with schistosome-positive faecal samples. A novel PCR-RFLP was designed targeting the Hpy166II recognition sequence in the mitochondrial gene sequence of S. indicum.

RESULT

The PCR using primers targeting the mitochondrial gene of S. spindale and S. indicum amplified a distinct product of approximately 454 bp with adult fluke as well as faecal DNA, which upon RFLP with Hpy166II yielded 330 bp and 124 bp products with S. indicum amplicons alone.

CONCLUSION

The novel PCR-RFLP possesses the potential to be used in epidemiological surveys among bovines and in snail intermediate hosts to screen for S. spindale and S. indicum infection.

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.

Schistosomiasis with a Focus on Africa

Schistosomiasis is a common neglected tropical disease of impoverished people and livestock in many developing countries in tropical Africa, the Middle East, Asia, and Latin America. Substantial progress has been made in controlling schistosomiasis in some African countries, but the disease still prevails in most parts of sub-Saharan Africa with an estimated 800 million people at risk of infection. Current control strategies rely primarily on treatment with praziquantel, as no vaccine is available; however, treatment alone does not prevent reinfection. There has been emphasis on the use of integrated approaches in the control and elimination of the disease in recent years with the development of health infrastructure and health education. However, there is a need to evaluate the present status of African schistosomiasis, primarily caused by Schistosoma mansoni and S. haematobium, and the factors affecting the disease as the basis for developing more effective control and elimination strategies in the future. This review provides an historical perspective of schistosomiasis in Africa and discusses the current status of control efforts in those countries where the disease is endemic.

Identification and Immunological Characterization of Somatic Proteins from Adults of Toxocara cati by Proteomics Technique

Background:

Toxocara cati is considered as one of the main etiological agents of toxocariasis with global and regional importance. As there is no information on proteomics of T. cati, herein, we reported the results obtained by proteomic analysis of somatic proteins extract, using a mass spectrometry (LC–MS/MS) approach.

Methods:

Somatic extract fractions were separated by two-dimensional SDS-PAGE and were electro blotted on to PVDF membranes for immunoblot analysis, then collected the immunogenic spots which response of antibodies of the paratenic hosts (mice) to the antigens (Mashhad, 2017), and analyzed by LC–MS/MS. The LC-MS/MS data were analyzed by Mascot database, Taxonomy Toxocara, and common contaminants, in Omics Center, Biotechnology Medical University of Graz (Austria, 2018).

Result:

The protein spots were isolated between 15–140 kDa ranges using 3–10 non-linear IPG strips and Brilliant Blue Coomassie. Ten proteins were characterized as immunogenic proteins, seven of them were identified and three of them were unknown proteins.

Conclusion:

This study provided additional information about the somatic antigens of T. cati, which can lead to the development of new strategies for novel immuno-modulators, drug targets, subunit vaccines and immunodiagnostic kits for toxocariasis.

Circulating cell-free mitochondrial DNA fragment: A possible marker for early detection of Schistosoma japonicum

Schistosomiasis is a major public health problem that is included in the neglected tropical diseases. The early diagnosis and detection of the pathogen are of critical importance in the control of the disease. The diagnostic techniques in use include the detection of worm's eggs in fecal examination or detection of circulating antigens in immunological based assays. These traditional strategies lack sensitivity in earlier detection of the schistosomiasis. Cell-free DNA (cfDNA) that includes the fragments of parasitic DNA circulating in the body fluids of host offers an alternative mean for the rapid pathogen detection and thus is a useful diagnostic tool. In this study, we explored the usefulness of the mitochondrial cfDNA markers for the diagnosis of schistosomiasis from the experimentally infected hosts (rabbits and mice). In this study we found mitochondrial DNA fragment cytochrome B gene as persistent and useful cfDNA marker for the early detection of schistosomiasis. We evaluated the sensitivity of cfDNA marker with varying numbers of cercaria. Overall, our results suggest that cfDNA markers can be useful for developing a diagnostic tool for the detection of S. japonicum infection.

Detection of circulating cell-free DNA to diagnose Schistosoma japonicum infection

Schistosomiasis occurs in 240 million people worldwide and is a major public health concern. Thus, early diagnosis and monitoring of schistosomiasis progression are needed to treat patients. Cell-free DNA (cfDNA) is present as fragments of parasite-derived DNA in host body fluids. Detection of this cfDNA in host blood may be a promising diagnostic marker of schistosomiasis. Therefore, in this study, we investigated the potential of internal transcribed spacer 2 (ITS2), a molecular taxonomy and barcoding marker, in diagnosing schistosomiasis using infected rabbit and mice sera. A 192 bp fragment of ITS2 was detected in the serum-isolated DNA from the infected host on different days after infection. We also determined the sensitivity of detecting ITS2 in mice with varying numbers of cercaria: cfDNA was present even in mice with low abundance of the parasite. Overall, our results show that cfDNA may be a potential tool for the early diagnosis and therapeutic evaluation of S. japonicum infection.

Field Evaluation of Recombinant Antigen ELISA in Detecting Zoonotic Schistosome Infection Among Water Buffaloes in Endemic Municipalities in the Philippines

In this study, we investigated the use of recombinant antigens thioredoxin peroxidase-1 (rSjTPx-1) and tandem repeat rSj1TR in evaluating the antibody positivity rates of Schistosoma japonicum infection among water buffaloes from four endemic areas in the Philippines, two municipalities with high endemicity (Calatrava, Negros Occidental and Catarman, Northern Samar) and two municipalities nearing elimination with no cases of human schistosomiasis (Talibon and Trinidad, Bohol). These recombinant antigen ELISA assays were compared with other diagnostic tests including SEA-ELISA, FECT, and fecal-based PCR. Results showed that rSj1TR-ELISA has the highest agreement with PCR in all study areas. Furthermore, significant positivity rates among water buffaloes were seen in Talibon and Trinidad, indicating that water buffaloes are maintaining the schistosome parasites in transmission areas even in the absence of human infection. Hence, serological assay using a more sensitive and specific rSj1TR-ELISA can be used for animal surveillance to prevent emergence and re-emergence of human schistosomiasis.

Proteomic analysis of soluble protein extract of adult Toxocara cati

Toxocara cati is a cat roundworm and the causative agent of toxocariasis as a cosmopolitan zoonotic disease. As no information has been reported so far, identification of T. cati proteins can be useful for the development of new diagnostic strategies. This study was conducted to identify the major proteins in the adult T. cati tegument using bi-dimensional electrophoresis (2-DE) and shotgun proteomics. A total proteins were identified, among them the metabolic enzymes were the largest group, including: Enolase, triose phosphate isomerase, fructose-bisphosphate aldolase, aldehyde dehydrogenase. The other important protein groups recognized in T. cati, belong to the HSP-family, the structure and motor proteins, such as actin. The role of these proteins have been implicated in parasite-host interactions and modulating cellular immune response, immune regulation in evasion mechanisms of the host immune response. Characterizing T. cati adult proteins play a key role not only in host-parasite interactions, but also in the discovery of drug targets, subunit vaccines against toxocariasis, immunodiagnostic kits for toxocariasis and the identification of novel immuno-modulators that can form the next generation of therapeutic possibilities for inflammatory diseases.

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.

Recent advances in nucleic acid-based methods for detection of helminth infections and the perspective of biosensors for future development

Pathogenic helminth infections are responsible for severe health problems and economic losses worldwide. Timely and accurate diagnosis of helminth infections is critical for adopting suitable strategies for pathogen control. Here, we review recent advances in nucleic acid-based diagnostic methods, including polymerase chain reaction, quantitative qPCR, loop-mediated isothermal amplification and recombinase polymerase amplification, and discuss their advantages and disadvantages for diagnosing helminth infections. In addition, we highlight recent advances in biosensors for the detection of nucleic acid biomarkers that can potentially be used for the diagnosis of helminth infection.

Detection of canine Schistosoma japonicum infection using recombinant thioredoxin peroxidase-1 and tandem repeat proteins

Humans and dogs live very close together and share various pathogens causing zoonotic parasitoses like schistosomiasis. A previous population genetics study done for schistosomes in the Philippines suggested that there is a high transmission level of Schistosoma japonicum among humans and dogs proving that the latter are important reservoirs for this zoonotic parasite. A more sensitive and specific test detecting schistosome infection in dogs will therefore strengthen the zoonotic surveillance, which might help in the possible elimination of this ancient disease. In this study, recombinant thioredoxin peroxidase-1 (SjTPx-1) and tandem repeat proteins (Sj1TR, Sj2TR, Sj4TR, Sj7TR) previously tested on human and water buffalo samples were used to assess its diagnostic applicability to dogs. Fifty-nine dog serum and stool samples were collected in the schistosomiasis-endemic municipalities of Calatrava, Negros Occidental and Catarman, Northern Samar in the Philippines and examined using the ELISA as compared to microscopy and fecal sample-based PCR. Samples positive for Babesia gibsoni and Dirofilaria immitis were also used to check for cross-reaction. Results showed that SjTPx-1 (80% sensitivity, 92.3% specificity) and Sj7TR (73.3% sensitivity, 92.3% specificity) have good potentials for diagnosing S. japonicum infection in dogs. These diagnostic antigens will therefore improve the surveillance in the transmission of the parasites from dogs to humans.

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.

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.

A novel copro-diagnostic molecular method for qualitative detection and identification of parasitic nematodes in amphibians and reptiles

Anthropogenic disturbance via resource acquisition, habitat fragmentation and climate change, amongst other factors, has led to catastrophic global biodiversity losses and species extinctions at an accelerating rate. Amphibians are currently one of the worst affected classes with at least a third of species categorised as being threatened with extinction. At the same time, they are also critically important for many habitats and provide man with a powerful proxy for ecosystem health by acting as a bioindicator group. Whilst the causes of synchronised amphibian losses are varied recent research has begun to highlight a growing role that macroparasites are playing in amphibian declines. However, diagnosing parasite infection in the field can be problematic, principally relying on collection and euthanasia of hosts, followed by necropsy and morphological identification of parasites in situ. The current study developed a non-invasive PCR-based methodology for sensitive detection and identification of parasitic nematode DNA released in the faeces of infected amphibians as egg or tissue fragments (environmental DNA). A DNA extraction protocol optimised for liberation of DNA from resilient parasite eggs was developed alongside the design of a novel, nematode universal, degenerate primer pair, thus avoiding the difficulties of using species specific primers in situations where common parasite species are unknown. Used in conjunction this protocol and primer pair was tested on a wide range of faecal samples from captive and wild amphibians. The primers and protocol were validated and detected infections, including a Railletnema nematode infection in poison dart frogs from ZSL London Zoo and Mantella cowani frogs in the wild. Furthermore, we demonstrate the efficacy of our PCR-based protocol for detecting nematode infection in other hosts, such as the presence of pinworm (Aspiculuris) in two tortoise species and whipworm (Trichuris muris) in mice. Our environmental DNA approach mitigates problems associated with microscopic identification and can be applied to detect nematode parasitoses in wild and captive hosts for infection surveillance and maintenance of healthy populations.

Copro-PCR based detection of bovine schistosome infection in India

Schistosomosis and amphistomosis are the two economically important and widely prevalent snail-borne trematode infections in grazing cattle of southern India. Acute infections are symptomatically similar and difficult to detect by routine microscopy for eggs. The present study was directed towards the development of a copro-polymerase chain reaction (copro-PCR) for detection of bovine schistosome species, using custom-designed primers targeting 18S and 28S ribosomal RNA as well as mitochondrial DNA. The study demonstrated the enhanced diagnostic specificity of mitochondrial DNA markers over ribosomal RNA genes as genus-specific probes to detect schistosomes. We developed a sensitive PCR assay using primers designed from mitochondrial DNA sequences targeting the partial rrnl (16S rRNA), tCys (transfer RNA for cysteine) and partial rrnS (12S rRNA) genes of Schistosoma spindale to specifically detect schistosome infection from faecal samples of naturally infected bovines. The salient findings of the work also throw light on to the high similarity of the ribosomal RNA gene sequences of schistosomes with those of Gastrothylax crumenifer and Fischoederius elongatus, the most prevalent pouched amphistomes of the region. Further investigation has to be directed towards unravelling the complete gene sequences of 18S and 28S ribosomal RNA as well as mitochondrial DNA sequences of amphistome isolates from India.

Molecular testing for clinical diagnosis and epidemiological investigations of intestinal parasitic infections

Over the past few decades, nucleic acid-based methods have been developed for the diagnosis of intestinal parasitic infections. Advantages of nucleic acid-based methods are numerous; typically, these include increased sensitivity and specificity and simpler standardization of diagnostic procedures. DNA samples can also be stored and used for genetic characterization and molecular typing, providing a valuable tool for surveys and surveillance studies. A variety of technologies have been applied, and some specific and general pitfalls and limitations have been identified. This review provides an overview of the multitude of methods that have been reported for the detection of intestinal parasites and offers some guidance in applying these methods in the clinical laboratory and in epidemiological studies.

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.

Advances in the Diagnosis of Human Schistosomiasis

Schistosomiasis is a major neglected tropical disease that afflicts more than 240 million people, including many children and young adults, in the tropics and subtropics. The disease is characterized by chronic infections with significant residual morbidity and is of considerable public health importance, with substantial socioeconomic impacts on impoverished communities. Morbidity reduction and eventual elimination through integrated intervention measures are the focuses of current schistosomiasis control programs. Precise diagnosis of schistosome infections, in both mammalian and snail intermediate hosts, will play a pivotal role in achieving these goals. Nevertheless, despite extensive efforts over several decades, the search for sensitive and specific diagnostics for schistosomiasis is ongoing. Here we review the area, paying attention to earlier approaches but emphasizing recent developments in the search for new diagnostics for schistosomiasis with practical applications in the research laboratory, the clinic, and the field. Careful and rigorous validation of these assays and their cost-effectiveness will be needed, however, prior to their adoption in support of policy decisions for national public health programs aimed at the control and elimination of schistosomiasis.

Rapid detection and identification of four major Schistosoma species by high-resolution melt (HRM) analysis

Schistosomiasis, caused by blood flukes belonging to several species of the genus Schistosoma, is a serious and widespread parasitic disease. Accurate and rapid differentiation of these etiological agents of animal and human schistosomiasis to species level can be difficult. We report a real-time PCR assay coupled with a high-resolution melt (HRM) assay targeting a portion of the nuclear 18S rDNA to detect, identify, and distinguish between four major blood fluke species (Schistosoma japonicum, Schistosoma mansoni, Schistosoma haematobium, and Schistosoma mekongi). Using this system, the Schistosoma spp. was accurately identified and could also be distinguished from all other trematode species with which they were compared. As little as 10(-5) ng genomic DNA from a Schistosoma sp. could be detected. This process is inexpensive, easy, and can be completed within 3 h. Examination of 21 representative Schistosoma samples from 15 geographical localities in seven endemic countries validated the value of the HRM detection assay and proved its reliability. The melting curves were characterized by peaks of 83.65 °C for S. japonicum and S. mekongi, 85.65 °C for S. mansoni, and 85.85 °C for S. haematobium. The present study developed a real-time PCR coupled with HRM analysis assay for detection and differential identification of S. mansoni, S. haematobium, S. japonicum, and S. mekongi. This method is rapid, sensitive, and inexpensive. It has important implications for epidemiological studies of Schistosoma.

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.

Detection of Schistosoma mansoni and Schistosoma haematobium by Real-Time PCR with High Resolution Melting Analysis

The present study describes a real-time PCR approach with high resolution melting-curve (HRM) assay developed for the detection and differentiation of Schistosoma mansoni and S. haematobium in fecal and urine samples collected from rural Yemen. The samples were screened by microscopy and PCR for the Schistosoma species infection. A pair of degenerate primers were designed targeting partial regions in the cytochrome oxidase subunit I (cox1) gene of S. mansoni and S. haematobium using real-time PCR-HRM assay. The overall prevalence of schistosomiasis was 31.8%; 23.8% of the participants were infected with S. haematobium and 9.3% were infected with S. mansoni. With regards to the intensity of infections, 22.1% and 77.9% of S. haematobium infections were of heavy and light intensities, respectively. Likewise, 8.1%, 40.5% and 51.4% of S. mansoni infections were of heavy, moderate and light intensities, respectively. The melting points were distinctive for S. mansoni and S. haematobium, categorized by peaks of 76.49 ± 0.25 °C and 75.43 ± 0.26 °C, respectively. HRM analysis showed high detection capability through the amplification of Schistosoma DNA with as low as 0.0001 ng/µL. Significant negative correlations were reported between the real-time PCR-HRM cycle threshold (Ct) values and microscopic egg counts for both S. mansoni in stool and S. haematobium in urine (p < 0.01). In conclusion, this closed-tube HRM protocol provides a potentially powerful screening molecular tool for the detection of S. mansoni and S. haematobium. It is a simple, rapid, accurate, and cost-effective method. Hence, this method is a good alternative approach to probe-based PCR assays.

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

Background

The Philippines has a population of approximately 103 million people, of which 6.7 million live in schistosomiasis-endemic areas with 1.8 million people being at risk of infection with Schistosoma japonicum. Although the country-wide prevalence of schistosomiasis japonica in the Philippines is relatively low, the prevalence of schistosomiasis can be high, approaching 65% in some endemic areas. Of the currently available microscopy-based diagnostic techniques for detecting schistosome infections in the Philippines and elsewhere, most exhibit varying diagnostic performances, with the Kato-Katz (KK) method having particularly poor sensitivity for detecting low intensity infections. This suggests that the actual prevalence of schistosomiasis japonica may be much higher than previous reports have indicated.

Methodology/Principal Findings

Six barangay (villages) were selected to determine the prevalence of S. japonicum in humans in the municipality of Palapag, Northern Samar. Fecal samples were collected from 560 humans and examined by the KK method and a validated real-time PCR (qPCR) assay. A high S. japonicum prevalence (90.2%) was revealed using qPCR whereas the KK method indicated a lower prevalence (22.9%). The geometric mean eggs per gram (GMEPG) determined by the qPCR was 36.5 and 11.5 by the KK. These results, particularly those obtained by the qPCR, indicate that the prevalence of schistosomiasis in this region of the Philippines is much higher than historically reported.

Conclusions/Significance

Despite being more expensive, qPCR can complement the KK procedure, particularly for surveillance and monitoring of areas where extensive schistosomiasis control has led to low prevalence and intensity infections and where schistosomiasis elimination is on the horizon, as for example in southern China.

Schistosomiasis is caused by infection with trematode blood flukes of the genus Schistosoma. Schistosoma japonicum is the causative agent of schistosomiasis in the Philippines, China and parts of Indonesia. In the Philippines, 6.7 million people live in endemic areas and 1.8 million are at risk of infection whereas concerted control efforts over the past 50 years in China have reduced the number of infected individuals considerably. Currently used microscopic techniques for diagnosis, notably the Kato-Katz (KK) technique, lack sensitivity in areas with low intensity schistosome infections. We have used a molecular diagnostic approach (qPCR), to assess the prevalence of S. japonicum in humans from six barangays in Northern Samar, the Philippines. The qPCR performed considerably better than the KK as a diagnostic procedure and could be an important tool in the future for surveillance and monitoring of areas where extensive schistosomiasis control has led to low prevalence and intensity infections and where schistosomiasis elimination is possible.

A loop-mediated isothermal amplification (LAMP) assay for early detection of Schistosoma mansoni in stool samples: a diagnostic approach in a murine model

BACKGROUND

Human schistosomiasis, mainly due to Schistosoma mansoni species, is one of the most prevalent parasitic diseases worldwide. To overcome the drawbacks of classical parasitological and serological methods in detecting S. mansoni infections, especially in acute stage of the disease, development of cost-effective, simple and rapid molecular methods is still needed for the diagnosis of schistosomiasis. A promising approach is the loop-mediated isothermal amplification (LAMP) technology. Compared to PCR-based assays, LAMP has the advantages of reaction simplicity, rapidity, specificity, cost-effectiveness and higher amplification efficiency. Additionally, as results can be inspected by the naked eye, the technique has great potential for use in low-income countries.

METHODOLOGY/PRINCIPAL FINDINGS

A sequence corresponding to a mitochondrial S. mansoni minisatellite DNA region was selected as a target for designing a LAMP-based method to detect S. mansoni DNA in stool samples. We used a S. mansoni murine model to obtain well defined stool and sera samples from infected mice with S. mansoni cercariae. Samples were taken weekly from week 0 to 8 post-infection and the Kato-Katz and ELISA techniques were used for monitoring the infection. Primer set designed were tested using a commercial reaction mixture for LAMP assay and an in house mixture to compare results. Specificity of LAMP was tested using 16 DNA samples from different parasites, including several Schistosoma species, and no cross-reactions were found. The detection limit of our LAMP assay (SmMIT-LAMP) was 1 fg of S. mansoni DNA. When testing stool samples from infected mice the SmMIT-LAMP detected S. mansoni DNA as soon as 1 week post-infection.

CONCLUSIONS/SIGNIFICANCE

We have developed, for the first time, a cost-effective, easy to perform, specific and sensitive LAMP assay for early detection of S. mansoni in stool samples. The method is potentially and readily adaptable for field diagnosis and disease surveillance in schistosomiasis-endemic areas.

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.

Pyrosequencing for rapid molecular identification of Schistosoma japonicum and S. mekongi eggs and cercariae

Schistosomiasis, which is caused by Schistosoma japonicum and S. mekongi, is a chronic and dangerous widespread disease affecting several countries in Asia. Differentiation between S. japonicum and S. mekongi eggs and/or cercariae via microscopic examination is difficult due to morphological similarities. It is important to identify these etiological agents isolated from animals and humans at the species or genotype level. In this study, a pyrosequencing assay designed to detect S. japonicum and S. mekongi DNA in fecal samples and infected snails was developed and evaluated as an alternative tool to diagnose schistosomiasis. New primers targeting the 18S ribosomal RNA gene were designated for specific amplification. S. japonicum and S. mekongi were identified using a 43-nucleotide pattern of the 18S ribosomal RNA gene and were differentiated using 7 nucleotides within this region. S. japonicum and S. mekongi-infected snails and fecal samples derived from infected mice and rats were differentially detected within a short period of time. The analytical sensitivity of the method enabled the identification of as little as a single cercaria artificially introduced into a pool of 10 non-infected snails and 2 eggs inoculated in 100mg of non-infected fecal sample. To evaluate the comparative efficacy of the assay, identical samples were also analyzed via microscopy and Sanger sequencing. The pyrosequencing technique was found to be superior to the microscopy method and more rapid than the Sanger sequencing method. These results suggest that the pyrosequencing assay is rapid, simple, sensitive and accurate in identifying S. japonicum and S. mekongi in intermediate hosts and fecal samples of the final host.

Long-term frozen storage of urine samples: a trouble to get PCR results in Schistosoma spp. DNA detection?

Background

Human schistosomiasis remains a serious worldwide public health problem. At present, a sensitive and specific assay for routine diagnosis of schistosome infection is not yet available. The potential for detecting schistosome-derived DNA by PCR-based methods in human clinical samples is currently being investigated as a diagnostic tool with potential application in routine schistosomiasis diagnosis. Collection of diagnostic samples such as stool or blood is usually difficult in some populations. However, urine is a biological sample that can be collected in a non-invasive method, easy to get from people of all ages and easy in management, but as a sample for PCR diagnosis is still not widely used. This could be due to the high variability in the reported efficiency of detection as a result of the high variation in urine samples’ storage or conditions for handling and DNA preservation and extraction methods.

Methodology/Principal Findings

We evaluate different commercial DNA extraction methods from a series of long-term frozen storage human urine samples from patients with parasitological confirmed schistosomiasis in order to assess the PCR effectiveness for Schistosoma spp. detection. Patientś urine samples were frozen for 18 months up to 7 years until use. Results were compared with those obtained in PCR assays using fresh healthy human urine artificially contaminated with Schistosoma mansoni DNA and urine samples from mice experimentally infected with S. mansoni cercariae stored frozen for at least 12 months before use. PCR results in fresh human artificial urine samples using different DNA based extraction methods were much more effective than those obtained when long-term frozen human urine samples were used as the source of DNA template.

Conclusions/Significance

Long-term frozen human urine samples are probably not a good source for DNA extraction for use as a template in PCR detection of Schistosoma spp., regardless of the DNA method of extraction used.

High prevalence of Schistosoma japonicum infection in Carabao from Samar Province, the Philippines: implications for transmission and control

Schistosoma japonicum is endemic in the Philippines, China and Indonesia, and infects more than 40 mammalian host species, all of which can act as reservoirs of infection. In China, water buffaloes have been shown to be major reservoirs of human infection. However, in the Philippines, carabao have not been considered important reservoir hosts for S. japonicum due to the low prevalence and infection intensities reported, the only exception being a qPCR-based study indicating 51% of carabao were S. japonicum-positive. However, the low prevalence found for the same animals when using conventional copro-parasitological techniques means that there is still confusion about the role of carabao in the transmission of schistosomiasis japonicum. To address this inconsistency, and to shed light on the potential role of carabao in the transmission of S. japonicum in the Philippines, we undertook a pilot survey, collecting fecal samples from animals in Western Samar Province and we used a combination of molecular and copro-parasitological techniques to determine the prevalence and intensity of S. japonicum. We found a high prevalence of S. japonicum in the carabao using a validated real-time PCR (qPCR) and a copro-parasitological tool, the formalin-ethyl acetate sedimentation (FEA-SD) technique. A much lower prevalence of S. japonicum was recorded for the same fecal samples using conventional PCR, the Kato-Katz technique and miracidial hatching. These results suggest that, due to their low diagnostic sensitivity, traditional copro-parasitological techniques underestimate infection in carabao. The use of FEA-SD and qPCR provides a more accurate diagnosis. Based on these findings, the role of bovines in the transmission of S. japonicum appears to be more important in the Philippines than previously recognized, and this may have significant implications for the future control of schistosomiasis there, particularly as, in contrast with previous surveys, we found an unprecedented high prevalence of S. japonicum in humans.

Schistosomiasis japonica is endemic in China, the Philippines and parts of Indonesia. Extensive research efforts have shown that water buffaloes are major reservoir hosts for transmission of Schistosoma japonicum in China. In contrast, comparatively fewer studies have been undertaken on the reservoir hosts for schistosomiasis japonica in the Philippines, although several reports have indicated that water buffaloes (carabao) are unimportant in transmission. Here, we undertook a pilot survey, using a new diagnostic tool (formalin-ethyl acetate sedimentation; FEASD), combined with real-time PCR (qPCR) for the detection of S. japonicum eggs in fecal samples, and report high prevalence of S. japonicum in carabao from Samar province. This study suggests that water buffaloes in the Philippines, as in China, are major reservoir hosts for the transmission of schistosomiasis. Future integrated control, including interventions targeting bovines, would likely reduce the prevalence of infection in humans.

The sources and metabolic dynamics of Schistosoma japonicum DNA in serum of the host

The polymerase chain reaction (PCR) assay has turned out to be one of the most potential tools for diagnosis of schistosomiasis. However, the source and metabolic dynamics of Schistosoma japonicum DNA in the blood of hosts is not clear. In this study, rabbit models with monosexual and mixed sexual cercariae infection were established to interpret the source of the parasite DNA in serum of the hosts. Following administration of praziquantel at 7 weeks postinfection, the metabolic mechanism of S. japonicum DNA in serum of the hosts was studied. The findings showed that, for the monosexual cercariae infection, the parasite DNA was detectable in serum of the host from day 3 to week 3 postinfection, while for the mixed sexual cercariae infection, the detection results were continually positive during the 7 weeks after infection. After treatment with praziquantel, detection of S. japonicum DNA in rabbit sera became positive at the second day posttreatment, and the positive period lasted 3 weeks in the monosexual cercariae infection group. However, with the mixed sexual cercariae infection group, the PCR results remained positive for 16 weeks after treatment. We conclude that the S. japonicum DNA in host serum primarily comes from the residual body of dead schistosomula and/or tegument shedding of worm growing in the first 4 weeks postinfection, while during the spawning stage of the female schistosome, the parasite DNA mainly comes from the disintegration of inactive eggs. The duration from treatment to total elimination of worm origin DNA in serum is not exceeding 3 weeks. However, the DNA release from inactive eggs can last for more than 16 weeks. Further studies are needed to address the sources and metabolic dynamics of S. japonicum DNA in human serum.

Sensitive and specific target sequences selected from retrotransposons of Schistosoma japonicum for the diagnosis of schistosomiasis

BACKGROUND

Schistosomiasis japonica is a serious debilitating and sometimes fatal disease. Accurate diagnostic tests play a key role in patient management and control of the disease. However, currently available diagnostic methods are not ideal, and the detection of the parasite DNA in blood samples has turned out to be one of the most promising tools for the diagnosis of schistosomiasis. In our previous investigations, a 230-bp sequence from the highly repetitive retrotransposon SjR2 was identified and it showed high sensitivity and specificity for detecting Schistosoma japonicum DNA in the sera of rabbit model and patients. Recently, 29 retrotransposons were found in S. japonicum genome by our group. The present study highlighted the key factors for selecting a new perspective sensitive target DNA sequence for the diagnosis of schistosomiasis, which can serve as example for other parasitic pathogens.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we demonstrated that the key factors based on the bioinformatic analysis for selecting target sequence are the higher genome proportion, repetitive complete copies and partial copies, and active ESTs than the others in the chromosome genome. New primers based on 25 novel retrotransposons and SjR2 were designed and their sensitivity and specificity for detecting S. japonicum DNA were compared. The results showed that a new 303-bp sequence from non-long terminal repeat (LTR) retrotransposon (SjCHGCS19) had high sensitivity and specificity. The 303-bp target sequence was amplified from the sera of rabbit model at 3 d post-infection by nested-PCR and it became negative at 17 weeks post-treatment. Furthermore, the percentage sensitivity of the nested-PCR was 97.67% in 43 serum samples of S. japonicum-infected patients.

CONCLUSIONS/SIGNIFICANCE

Our findings highlighted the key factors based on the bioinformatic analysis for selecting target sequence from S. japonicum genome, which provide basis for establishing powerful molecular diagnostic techniques that can be used for monitoring early infection and therapy efficacy to support schistosomiasis control programs.

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

Schistosomiasis is a major infectious disease and a public health concern in many areas in China and other countries. Sensitive method for detection of the parasite is critical for early diagnosis and for monitoring of effective treatment of the disease. In this study, we developed a highly sensitive TaqMan real-time PCR assay for the detection of Schistosoma japonicum DNA in mouse feces and serum samples. This assay was based on the DNA sequence of the S. japonicum 18S rRNA gene and was able to detect 10 fg of S. japonicum genomic DNA, which is 100 times more sensitive than conventional PCR. We were able to detect the S. japonicum DNA one week post-infection in mouse sera and 4 weeks post-infection in feces, which was one week earlier than egg detection by microscopy in feces. This assay was also highly specific for Asian Schistosomes which are causative species of human Schistosomiasis. In single sex male cercariae infected mice, parasite DNA was only detected in the first 4 weeks post-infection, suggesting that the DNA was derived from decaying worms' corpse in the first 4 weeks whereas the DNA was mainly from decaying parasite eggs afterwards. Therefore we conclude that the established TaqMan real-time PCR assay is a sensitive, specific and convenient method that could be used for the early diagnostic evaluation of S. japonicum infection in humans and for monitoring outbreaks in endemic areas with low prevalence.

Schistosomiasis in the People's Republic of China: the era of the Three Gorges Dam

The potential impact of the Three Gorges Dam (TGD) on schistosomiasis transmission in China has invoked considerable global concern. The TGD will result in changes in the water level and silt deposition downstream, favoring the reproduction of Oncomelania snails. Combined with blockages of the Yangtze River's tributaries, these changes will increase the schistosomiasis transmission season within the marshlands along the middle and lower reaches of the Yangtze River. The changing schistosome transmission dynamics necessitate a comprehensive strategy to control schistosomiasis. This review discusses aspects of the epidemiology and transmission of Schistosoma japonicum in China and considers the pathology, clinical outcomes, diagnosis, treatment, immunobiology, and genetics of schistosomiasis japonica together with an overview of current progress in vaccine development, all of which will have an impact on future control efforts. The use of synchronous praziquantel (PZQ) chemotherapy for humans and domestic animals is only temporarily effective, as schistosome reinfection occurs rapidly. Drug delivery requires a substantial infrastructure to regularly cover all parts of an area of endemicity. This makes chemotherapy expensive and, as compliance is often low, a less than satisfactory control option. There is increasing disquiet about the possibility that PZQ-resistant schistosomes will develop. Consequently, as mathematical modeling predicts, vaccine strategies represent an essential component in the future control of schistosomiasis in China. With the inclusion of focal mollusciciding, improvements in sanitation, and health education into the control scenario, China's target of reducing the level of schistosome infection to less than 1% by 2015 may be achievable.

High prevalence of Schistosoma japonicum infection in water buffaloes in the Philippines assessed by real-time polymerase chain reaction

Difficulty in controlling human Schistosoma japonicum infection is partly attributed to the presence of non-human definitive hosts. Water buffaloes are a major reservoir for transmission of S. japonicum to humans in China. However, in the Philippines, reports based on microscopic examination of buffalo stool identified a low prevalence of S. japonicum, and mathematical models using these data concluded that water buffaloes are not a major reservoir for transmission of S. japonicum to humans. We collected stool from 81 buffaloes in Macanip, Leyte, the Philippines, and assayed for S. japonicum infection by the Danish Bilharziasis Laboratory technique, the Kato-Katz technique, miracidia hatching, and a highly validated real-time polymerase chain reaction. The prevalence defined by each assay was 3.7%, 3.7%, 0%, and 51.5% respectively. Our results demonstrate that microscopic-based techniques dramatically underestimate the prevalence of S. japonicum infection in water buffaloes in the Philippines and warrant reexamination of the role of bovines in transmission of S. japonicum to humans in the Philippines.

Identification and differentiation of human schistosomes by polymerase chain reaction

Recent increasing number of travelers, immigrants and foreign workers from schistosomiasis endemic area has thus resulted in the importation of schistosomiasis to non-endemic countries. To avoid ova-induced pathogenicity, sensitive and specific diagnostic means at an early stage of infection are therefore crucial. In this study, we developed polymerase chain reaction (PCR) primers specific for human schistosome species. The PCR products were obtained in a species-specific manner (479 bp, Schistosoma mansoni; 365 bp, S. haematobium; 614 bp, S. japonicum; 303 bp, S. mekongi) and were detectable from 0.01 pg of total worm DNA (S. haematobium, S. japonicum, S. mekongi). The primer sets were also available for multiplex use. Although some difficulties were experienced in amplifying the parasite DNA from the infected animals, schistosome DNA could be detected from one day post infection. The PCR method described herein will therefore be beneficial to detect human schistosomiasis, after some improvements in this method.

Sensitive and rapid detection of Schistosoma japonicum DNA by loop-mediated isothermal amplification (LAMP)

In this study, a loop-mediated isothermal amplification (LAMP) assay was established to detect Schistosoma japonicum DNA in faecal and serum samples of rabbits, and serum samples of humans infected with S. japonicum. This LAMP assay was based on the sequence of highly repetitive retrotransposon SjR2, and was able to detect 0.08 fg S. japonicum DNA, which is 10(4) times more sensitive than conventional PCR. The LAMP assay was also highly specific for S. japonicum and able to detect S. japonicum DNA in rabbit sera at 1 week p.i. Following administration of praziquantel, detection of S. japonicum DNA in rabbit sera became negative at 12 weeks post-treatment. These results demonstrated that LAMP was effective for early diagnosis of, and evaluation of therapy effectiveness for, S. japonicum infection. Both PCR and LAMP assays were then used to detect S. japonicum DNA in 30 serum samples from S. japonicum-infected patients and 20 serum samples from healthy persons. The percentage sensitivity of LAMP was 96.7%, whereas that of PCR was only 60%, indicating that LAMP was more sensitive than conventional PCR for clinical diagnosis of schistosomiasis cases in endemic areas. The established LAMP assay should provide a useful and practical tool for the routine diagnosis and therapeutic evaluation of human schistosomiasis.

Real-time PCR for detection of low intensity Schistosoma japonicum infections in a pig model

Decades of successful Schistosoma japonicum control have increased the interest in how to diagnose low intensity infections. A real-time PCR assay targeting the mitochondrial NADH dehydrogenase I gene in S. japonicum was evaluated in infected pigs with very low egg output. Six out of 12 S. japonicum infected pigs were treated with praziquantel 8 weeks after infection and all pigs were followed for 16 weeks post-infection. One commercial and one non-commercial extraction method were evaluated in combination with PCR on faecal samples. PCR with either extraction method were equally sensitive as the DBL-filtration/sedimentation technique in the acute, productive stage. PCR recovered slightly more positive samples in the chronic stage, but most faecal samples were negative for both PCR and microscopy from week 9 post-infection irrespective of treatment. IgG antibody titers against soluble egg antigen IgG remained high throughout the study in both the treated and non-treated group. PCR was consistently negative in serum and urine samples and negative in most of the caecal biopsies. We conclude that the S. japonicum faecal PCR is a highly sensitive test. However, in clinical samples when faecal egg output almost reaches nil in the chronic stage despite persistent worm burdens, both the faecal PCR and microscopy results were negative. Real-time PCR is less labour intensive than most microscopy methods, but has a higher material cost per sample.

Genetic filtering and optimal sampling of Schistosoma mansoni populations

Allelic variation in 6 microsatellite markers was compared between frozen Schistosoma mansoni eggs and laboratory-passaged worms originating from the same 5 fecal samples obtained from Brazilian residents. Based on allelic richness values, the number of alleles detected per locus did not differ between egg and worm DNA templates. However, our ability to score loci differed between these DNA templates, with worms providing more scored loci per individual than eggs. Differences also existed between the worms and eggs in the identity of the specific alleles that were detected. Additionally, we observed a reduction in homozygous genotypes among laboratory-passaged worms relative to the eggs. Allelic diversity curves were calculated by genotyping all worms from a representative host sample to determine the relationship between the number of alleles detected at a locus and the number of worms genotyped. Curves for the 5 residents' worm infrapopulations for each of the loci were very similar. The equation y=19.55 x ln(x) + 9.992 explained the association between sampling effort (x) and number of alleles detected (y) with an R(2) of 0.775. In conclusion, egg DNA templates and allelic diversity curves can benefit efforts to discern the sociological, ecological and evolutionary forces impacting the genetic diversity and disease epidemiology of human schistosomes.