Diagnosis of Wuchereria bancrofti infection by the polymerase chain reaction using urine and day blood samples from amicrofilaraemic patients

Diagnosis of echinococcosis by detecting circulating cell-free DNA and miRNA

INTRODUCTION

Diagnosis of echinococcosis is difficult and usually performed based on clinical findings, imaging, and serological test. However, all of them have limitations, especially in follow-up approaches.

AREAS COVERED

Detection of cell-free DNA (cfDNA) and micro-RNA (miRNA) is currently a hot topic for diagnosis of echinococcosis diseases. For detecting cell-free DNA in echinococcosis patient's samples such as sera, some techniques are based on next-generation sequencing (NGS), DNA-deep sequencing, some are based on PCR-based methods, and a few works related to the detection of miRNA for the diagnosis of human echinococcosis.

EXPERT OPINION

In the detection of cell-free DNA in echinococcosis patient' samples, NGS and DNA-deep sequencing have shown high level of sensitivity, but are not suitable for routine clinical examination as they are expensive and inaccessible in the majority of endemic areas. However, PCR-based methods have shown a sensitivity of about 20-25%. To improve the sensitivity of these tests, improving the DNA extraction method, designing appropriate primers for detecting short-length fragments of circulating DNA, using a higher volume of a serum sample, and application of more sensitive PCR methods are recommended. In the field of miRNA detection, further works are recommended.

An update on non-invasive urine diagnostics for human-infecting parasitic helminths: what more could be done and how?

Reliable diagnosis of human helminth infection(s) is essential for ongoing disease surveillance and disease elimination. Current WHO-recommended diagnostic assays are unreliable in low-endemic near-elimination settings and typically involve the invasive, onerous and potentially hazardous sampling of bodily fluids such as stool and blood, as well as tissue via biopsy. In contrast, diagnosis by use of non-invasive urine sampling is generally painless, more convenient and low risk. It negates the need for specialist staff, can usually be obtained immediately upon request and is better accepted by patients. In some instances, urine-based diagnostic assays have also been shown to provide a more reliable diagnosis of infection when compared to traditional methods that require alternative and more invasive bodily samples, particularly in low-endemicity settings. Given these relative benefits, we identify and review current research literature to evaluate whether non-invasive urine sampling is currently exploited to its full potential in the development of diagnostic tools for human helminthiases. Though further development, assessment and validation are needed before their routine use in control programmes, low-cost, rapid and reliable assays capable of detecting transrenal helminth-derived antigens and cell-free DNA show excellent promise for future use at the point-of-care in high-, medium- and even low-endemicity elimination settings.

Review of Dancing Parasites in Lymphatic Filariasis

Lymphatic filariasis is an infection transmitted by blood-sucking mosquitoes with filarial nematodes of the species Wuchereria bancrofti, Brugia malayi und B. timori . It is prevalent in tropical countries throughout the world, with more than 60 million people infected and more than 1 billion living in areas with the risk of transmission. Worm larvae with a length of less than 1 mm are transmitted by mosquitoes, develop in human lymphatic tissue to adult worms with a length of 7-10 cm, live in the human body for up to 10 years and produce millions of microfilariae, which can be transmitted further by mosquitoes. The adult worms can be easily observed by ultrasonography because of their size and fast movements (the so-called "filarial dance sign"), which can be differentiated from other movements (e. g., blood in venous vessels) by their characteristic movement profile in pulsed-wave Doppler mode. Therapeutic options include (combinations of) ivermectin, albendazole, diethylcarbamazine and doxycycline. The latter depletes endosymbiotic Wolbachia bacteria from the worms and thus sterilizes and later kills the adult worms (macrofilaricidal or adulticidal effect).

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.

Detection of Dirofilaria immitis DNA in host serum by nested PCR

The heartworm Dirofilaria immitis is the causative agent of dirofilariasis in dogs. Studies have shown that parasite-derived cell-free DNA (cfDNA) can be detected in host blood and may be a promising diagnostic marker for parasitic infections. Thus, our aim was to detect D. immitis-derived cfDNA in host serum by nested PCR. Sera were collected from 12 dogs with natural D. immitis infections; eight were microfilaria (mf)-positive, and the remaining four were mf-negative. Culture fluids derived from single-sex adult D. immitis worms (mf-producing females and males) were also tested for cfDNA. All mf-positive sera were positive by nested PCR, whereas no amplification products were detected in mf-negative sera. The culture fluid of mf-producing females was positive by nested PCR but that of males was negative. All products amplified by nested PCR were sequenced to confirm that the amplicons were those of D. immitis. These results indicate that D. immitis DNA circulates freely in dog serum, except in mf-negative dogs. Additionally, D. immitis cfDNA may primarily be derived from the mf, and adult worms appeared to be minor contributors of cfDNA concentrations in serum; however, the contribution of D. immitis cfDNA derived from larvae of other developmental stages is unclear. An evaluation of the kinetics of D. immitis cfDNA in host serum throughout the parasite life cycle could facilitate the development of early molecular diagnostic techniques. To the best of our knowledge, this is the first report of the detection of mitochondrial DNA from a filarial parasite in host serum.

Detection of Wuchereria bancrofti DNA in paired serum and urine samples using polymerase chain reaction-based systems

The Global Program for the Elimination of Lymphatic Filariasis (GPELF) aims to eliminate this disease by the year 2020. However, the development of more specific and sensitive tests is important for the success of the GPELF. The present study aimed to standardise polymerase chain reaction (PCR)-based systems for the diagnosis of filariasis in serum and urine. Twenty paired biological urine and serum samples from individuals already known to be positive for Wuchereria bancrofti were collected during the day. Conventional PCR and semi-nested PCR assays were optimised. The detection limit of the technique for purified W. bancrofti DNA extracted from adult worms was 10 fg for the internal systems (WbF/Wb2) and 0.1 fg by using semi-nested PCR. The specificity of the primers was confirmed experimentally by amplification of 1 ng of purified genomic DNA from other species of parasites. Evaluation of the paired urine and serum samples by the semi-nested PCR technique indicated only two of the 20 tested individuals were positive, whereas the simple internal PCR system (WbF/Wb2), which has highly promising performance, revealed that all the patients were positive using both samples. This study successfully demonstrated the possibility of using the PCR technique on urine for the diagnosis of W. bancrofti infection.

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.

Experimental study for early diagnosis of prepatent schistosomiasis mansoni by detection of free circulating DNA in serum

Sensitive and specific diagnostic methods of schistosomiasis at an early stage of infection are crucial to avoid irreversible pathological reactions induced by eggs. This study aimed to evaluate the PCR technique for detection of free circulating Schistosoma mansoni DNA in serum in the early prepatent period in experimentally infected mice, in comparison to the commonly used indirect hemagglutination assay (IHA) for the detection of bilharzial antibody and stool examination. Sixty-four mice were experimentally infected with S. mansoni, and every 3 or 4 days through the 8 weeks postinfection (p.i.), serum samples were collected from randomly chosen four infected mice, then pooled and examined for circulating DNA and bilharzial antibody. The results showed that the earliest deposition of eggs in the small intestine was observed at the fifth week p.i., and the eggs were detected in feces in the seventh week p.i. PCR detected free circulating DNA of S. mansoni starting from the third day p.i., while IHA failed to detect infection up to the eighth week p.i. It is concluded that detection of free circulating DNA by PCR can be used as a valuable test for early diagnosis of prepatent S. mansoni infection.

Cost-effective antigen testing for delimitation, monitoring and evaluation in bancroftian filariasis

This study was focussed on identifying a cost-effective method for delimitation, monitoring and evaluation in bancroftian filariasis. Finger prick blood samples were collected between 20.00 and 23.00 hours for the detection of microfilariae (mf) from the available population in a village which was endemic for lymphatic filariasis. Simultaneously, from each individual, four spots of 25-μl blood samples were collected on Whatman number 3 filter paper and air dried. Dried filter paper spots were pooled in quantities of 1, 5, 10, 15, 20 and 25 on unknown and simulated mf and antigen prevalence. Pooled samples were assayed for circulating filarial antigen (CFA) using TropBIO Og4C3 ELISA kits. The community mf and CFA rates were 3.4% and 25.9%, respectively. The pool sizes of 20 and 25 showed CFA positivity in all the above categories tested. The results of the pooled blood spot samples suggest that, in areas with mf and CFA prevalence rates between 1 and 10%, pools of 20 or 25 could be considered as the ideal pool size for the detection of filarial infection in the community. CFA prevalence at the level of 5-6% following desirable rounds of mass drug administration (MDA) indicates that the community mf prevalence is likely to be at the 1% level.

Detection and discrimination of Loa loa, Mansonella perstans and Wuchereria bancrofti by PCR-RFLP and nested-PCR of ribosomal DNA ITS1 region

The ribosomal deoxyribonucleic acid (DNA) internal transcribed spacer region (ITS1) of two filarial nematodes, Loa loa and Mansonella perstans, was amplified and further sequenced to develop an species-specific polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) protocol for the differentiation of both species from Wuchereria bancrofti, three filarial nematodes with blood circulating microfilariae. The ITS1-PCR product digested with the restriction endonuclease Ase I generated an specific diagnostic pattern for each of the three species. Moreover, three new specific nested-PCRs, targeting the ITS1 region, for differential detection of L. loa, M. perstans and W. bancrofti were developed and used when the ITS1-PCR products were insufficient for the Ase I enzymatic digestion. These filarial species-specific molecular protocols were evaluated in forty blood samples from African adult immigrants attending in the Hospital Insular of Gran Canaria, Canarias, Spain.

A salting out and resin procedure for extracting Schistosoma mansoni DNA from human urine samples

Background

In this paper a simple and cheap salting out and resin (InstaGene matrix^® resin - BioRad) DNA extraction method from urine for PCR assays is introduced. The DNA of the fluke Schistosoma mansoni was chosen as the target since schistosomiasis lacks a suitable diagnostic tool which is sensitive enough to detect low worm burden. It is well known that the PCR technique provides high sensitivity and specificity in detecting parasite DNA. Therefore it is of paramount importance to take advantage of its excellent performance by providing a simple to handle and reliable DNA extraction procedure, which permits the diagnosis of the disease in easily obtainable urine samples.

Findings

The description of the extraction procedure is given. This extraction procedure was tested for reproducibility and efficiency in artificially contaminated human urine samples. The reproducibility reached 100%, showing positive results in 5 assay repetitions of 5 tested samples each containing 20 ng DNA/5 ml. The efficiency of the extraction procedure was also evaluated in a serial dilution of the original 20 ng DNA/5 ml sample. Detectable DNA was extracted when it was at a concentration of 1.28 pg DNA/mL, revealing the high efficiency of this procedure.

Conclusions

This methodology represents a promising tool for schistosomiasis diagnosis utilizing a bio-molecular technique in urine samples which is now ready to be tested under field conditions and may be applicable to the diagnosis of other parasitic diseases.

Molecular approaches for the detection of Schistosoma mansoni: possible applications in the detection of snail infection, monitoring of transmission sites, and diagnosis of human infection

The detection of specific DNA sequences by polymerase chain reaction (PCR) has proved extremely valuable for the analysis of genetic disorders and the diagnosis of a variety of infectious disease pathogens. However, the application to the detection of Schistosoma mansoni is rare, despite a recommendation of the World Health Organization that a major focus of research on schistosomiasis should be on the development and evaluation of new strategies and tools for control of the disease. In this context, a few studies were published for the detection of the parasite in snails, monitoring of cercariae in water bodies, and diagnosis of human infection. The present minireview describes sensitive and specific PCR based systems to detect S. mansoni, indicating possible applications in the detection of snail infection, monitoring of transmission sites, and diagnosis of human infection.

The development and evaluation of a single step multiplex PCR method for simultaneous detection of Brugia malayi and Wuchereria bancrofti

A single step novel multiplex polymerase chain reaction (PCR) has been developed for simultaneous detection of human filarial parasites, Brugia malayi and Wuchereria bancrofti, from blood samples and mosquitoes. The primers used were novel and have been tested with the parasite DNA amplifying 188bp (BM) and 129bp (WB) DNA fragments, specific to B. malayi and W. bancrofti, respectively, in a single reaction. The specificity of the PCR product was confirmed by DNA sequencing and slot blot hybridization assay. The test was found highly sensitive for both B. malayi and W. bancrofti by detecting the parasitaemia up to the level of one microfilaria per reaction. The assay was further evaluated on 98 blood samples and 144 mosquito samples collected from filarial endemic areas. The PCR was found to be more efficient in comparison to microscopy by detecting 8% and 5% more filarial parasites in field-collected blood and mosquito samples, respectively. This novel PCR that offers scope for simultaneous detection of both the parasites may be used as a diagnostic tool for the detection of filariasis in population and can be adopted for rapid surveillance and monitoring of mosquitoes for use in the effective control of filariasis.

A new PCR-based approach for the specific amplification of DNA from different Schistosoma species applicable to human urine samples

Currently available methods for the diagnosis of human schistosomiasis often lack enough sensitivity and specificity. Recently, several authors have developed more specific and sensitive diagnostic methods, mainly based on the polymerase chain reaction (PCR) technique. Nevertheless, these have been only applied for the diagnosis of 1 out of 4 Schistosoma species affecting man (S. mansoni). Additionally, application of specific PCR has been exclusively used for blood or faecal patients' samples. Here, we develop a new, high sensitive PCR approach that allows the genus- and species-specific amplification of the main 4 Schistosoma species causing disease in man plus S. bovis. We further successfully apply this technique for the detection of parasite DNA in easy-to-handle urine samples from patients with schistosomiasis. With these samples, we have found 94.4% sensitivity and 99.9% specificity when applying a genus-specific (Schistosoma spp.) primer pair, and 100% sensitivity and 98.9% specificity in a species-specific (S. mansoni) PCR.

Schistosoma mansoni: a diagnostic approach to detect acute schistosomiasis infection in a murine model by PCR

Schistosomiasis represents an increasing problem in non-endemic areas, due to the growing number of immigrants and to tourists contracting this disease in "off-the-beaten-track" tourism. Acute schistosomiasis is not diagnosed early due to the lack of diagnostic tools that are sufficiently sensitive enough to detect the parasite during the first weeks of infection. We have developed a diagnostic approach based on the detection of parasite DNA by polymerase chain reaction (PCR) in urine, comparing the performance of this new approach with the two currently used schistosomiasis diagnostic tools (Kato-Katz and ELISA) and the PCR in stool samples. This comparison was done in a Schistosoma mansoni murine experimental model, which permits follow up of the parasite from the acute to the chronic stage of infection. Our results suggest that this new PCR-based approach could be useful for the detection of acute schistosomiasis in easy-to-handle clinical samples such the urine.

Combined detection of Brugia malayi and Wuchereria bancrofti using single PCR

A single step PCR method has been developed for the combined detection of the human filarial parasites, Brugia malayi and Wuchereria bancrofti. Parasites' DNA were isolated from filaria positive blood samples that were collected from endemic areas. The primers used were Hha1 and Ssp I, which amplified the DNA fragments of 322 bp and 188 bp specific to B. malayi and W. bancrofti, respectively. The sensitivity of the assay was tested with blood and mosquito samples having one W. bancrofti in a pool of 10 B. malayi. The assay was further evaluated on field collected blood and mosquito samples. Use of this assay as a diagnostic tool for the detection of filariasis being the most promising aspect of this study, offers scope for detection of both the parasites even at low levels of infection.

Diagnosis of human filariases (except onchocerciasis)

The traditional method of diagnosing filarial infections is to examine blood or skin samples for microfilariae and for many this is still the standard procedure. However, since the present global campaign to eliminate lymphatic filariasis new diagnostic tools have emerged like PCR, antigen detection using finger-prick blood taken during the day and ultrasound to visualize adult worms. The last two can be applied in endemic countries with limited resources and enable the detection of early infections. As well as their value in control schemes, the latter is particularly important for the individual since recent research has shown that damage is usually caused long before symptoms appear. The usefulness in different situations and the advantages and disadvantages of the various new tools for diagnosis of lymphatic filariasis are discussed. For loiasis, immunodiagnostic methods have not been very successful but repetitive DNA sequences in the Loa genome have been found to be species specific. Techniques based on them are particularly useful for diagnosing cases of occult infection without microfilaraemia. There have been no advances in the diagnosis of Mansonella perstans but both immunodiagnostic and PCR tests show promise in differentiating M. streptocerca, and the latter in differentiating M.ozzardi, from Onchocerca. In addition to the human filariae, the dog parasites Dirofilaria immitis and D. repens can also occur in humans but do not produce microfilariae in them. ELISAs and PCR probes have been devised and can usefully differentiate between pulmonary dirofilariasis and lung cancer.

Lymphatic filariasis: new insights into an old disease

Lymphatic filariasis has afflicted people in the tropical areas of the world for thousands of years but even up to comparatively recent times it has been poorly understood and its importance under recognised. In the last 2 decades or so there has been a flurry of activity in filariasis research, which has provided new insights into the global problem of filariasis, the pathogenesis of filarial disease, diagnosis and control.

Recent advances in molecular diagnostic techniques for human lymphatic filariasis and their use in epidemiological research

Diagnosis of lymphatic filariasis for epidemiological studies is an area of science that has been greatly modernized over the last two decades. Recent developments and the introduction of new technologies have led to the replacement of traditional diagnostic methods that were insensitive, tedious and often impractical with molecular biology techniques that have considerable potential for field use. This paper reviews some of these major new techniques and the applications of molecular diagnosis in the field of lymphatic filariasis.

Evaluation of PCR-based methods for the diagnosis of infection in bancroftian filariasis

The value of the polymerase chain reaction (PCR) in the diagnosis of Wuchereria bancrofti infection was evaluated in comparison to microscopical examination of night blood smears, Nuclepore filtration, serology and ultrasonography. No correlation was found between PCR-based deoxyribonucleic acid (DNA) probing and serology. We did not find any evidence of free filarial DNA in either blood plasma or chylocoele fluid. We conclude that the 2 PCR-based techniques evaluated are not more sensitive than Nuclepore filtration for detection of W. bancrofti microfilaraemia, need at least 1 intact microfilaria in the volume of blood used for DNA extraction, and were much inferior to ultrasonography for detection of amicrofilaraemic adult worm carriers.

Lymphatic filariasis in the Philippines

Lymphatic filariasis caused by Wuchereria bancrofti and Brugia malayi is endemic throughout most of the southern half of the Philippine archipelago. Economic and manpower shortages prior to 1996 made it difficult to acquire new prevalence data and vector control data concurrently from all provinces. Nevertheless, analysis of cumulative prevalence data on filariasis indicates the persistence of filariasis in each of the three major island groups - Luzon, Visayas and Mindanao - including 45 out of 77 provinces. Here, Michael Kron and colleagues summarize the prevalence data, and review host, parasite and vector characteristics relevant to the design and implementation of disease control initiatives in the Philippines planned for the year 2000.

The control of the human filariases

There is a growing momentum for the global control and elimination of the major human filariases as public health problems worldwide. The renewed optimism for undertaking this objective reflects the development of simple and potentially cost-effective strategies for mass drug delivery in onchocerciasis and the availability of new extremely effective drug combinations to treat infection, and new methods of morbidity control in lymphatic filariasis. It also reflects the development and current availability of very effective diagnostic, surveillance and control modeling tools for both parasites. Control programming will also be aided by our greater understanding of the biology of transmission, host immunity and disease pathogenesis.

Sequence conservation of repeat 3 region of the gene coding for the 15 kDa polyprotein within human and simian Loa loa

The human and simian strains of Loa loa microfilariae are morphologically identical even though their periodicities vary. When using primate models (Mandrillus sphinx) of human loaisis for vaccination trials, the absence of any ongoing simian L. loa infection must be demonstrated. Nested primers derived from a human strain of L. loa (targeted on the repeat 3 region of the gene encoding the 15 kDa polyprotein; 15r3) amplified at 366 bp sequence from simian L. loa genomic DNA and blood lysates from mandrills infected with simian L. loa. This nested-PCR assay has been tested on 12 amicrofilaremic (AMF) mandrills (without filarial microfilariae) and was positive in four mandrills. The nested-PCR product derived from simian L. loa genomic DNA and from three of four AMF mandrills has been sequenced. No difference was observed between the four sequences, which, in addition, were 99.18% identical to the 15r3 of human L. loa. Therefore, the 15r3 sequence is conserved within human and simian L. loa. These results suggest that the four PCR-positive mandrills without circulating microfilariae had occult simian L. loa infections. The study demonstrates the ability of a nested-PCR assay to identify animals naturally infected with simian L. loa.