Magnetic bead antigen capture enzyme-linked immunoassay in microtitre trays for rapid detection of schistosomal circulating anodic antigen

UCP-LF and other assay methods for schistosome circulating anodic antigen between 1978 and 2022

Detection of circulating anodic antigen (CAA) is known for its high sensitivity in diagnosing schistosomiasis infection, even in low-prevalence settings. The Up-Converting Phosphor-Lateral Flow (UCP-LF) assay developed in 2008 presented greater sensitivity than other assay methods in use for CAA detection. Our study aims to comprehensively review all studies conducted in this area and thus generate informed conclusions on the potential for adopting the UCP-LF assay for diagnosing this important yet neglected tropical disease. Using the Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines, we generated search criteria to capture all studies in English journals available in the Scopus and PubMed databases on 20 December 2022. A total of 219 articles were identified, and 84 that met the inclusion criteria were retrieved and eventually included in the study. Twelve different assay methods were identified with a noteworthy transition from enzyme-linked immunosorbent assay (ELISA) to the UCP-LF assay, a laboratory-based assay that may be applicable as a point-of-care (POC) diagnostic test for schistosomiasis. Reducing the time, cost, and dependence on specialized laboratory skills and equipment, especially relating to the trichloroacetic acid extraction step and centrifugation in the UCP-LF CAA assay may go a long way to aid its potential as a POC tool. We also propose the development of a CAA-specific aptamer (short protein/antigen-binding oligonucleotide) as a possible alternative to monoclonal antibodies in the assay. UCP-LF has great potential for POC application.

The ER Stress/UPR Axis in Chronic Obstructive Pulmonary Disease and Idiopathic Pulmonary Fibrosis

Cellular protein homeostasis in the lungs is constantly disrupted by recurrent exposure to various external and internal stressors, which may cause considerable protein secretion pressure on the endoplasmic reticulum (ER), resulting in the survival and differentiation of these cell types to meet the increased functional demands. Cells are able to induce a highly conserved adaptive mechanism, known as the unfolded protein response (UPR), to manage such stresses. UPR dysregulation and ER stress are involved in numerous human illnesses, such as metabolic syndrome, fibrotic diseases, and neurodegeneration, and cancer. Therefore, effective and specific compounds targeting the UPR pathway are being considered as potential therapies. This review focuses on the impact of both external and internal stressors on the ER in idiopathic pulmonary fibrosis (IPF) and chronic obstructive pulmonary disease (COPD) and discusses the role of the UPR signaling pathway activation in the control of cellular damage and specifically highlights the potential involvement of non-coding RNAs in COPD. Summaries of pathogenic mechanisms associated with the ER stress/UPR axis contributing to IPF and COPD, and promising pharmacological intervention strategies, are also presented.

Microplate magnetic chemiluminescence immunoassay for detecting urinary survivin in bladder cancer

Survivin is a tumor marker for bladder cancer; however the role of urinary survivin levels has not been fully elucidated due to the limitations of current detection methods. Based on two survivin-specific monoclonal antibodies (McAbs) already confirmed through enzyme linked immunosorbent assays, the present study aimed to establish a microplate magnetic chemiluminescence immunoassay (CLIA) for the detection of urinary survivin levels and evaluate its application for the diagnosis of patients with bladder cancer. Horseradish peroxidase and biotin conjugates were used to label two different anti-survivin McAbs, respectively. The labeled antibodies combined with survivin to form a sandwiched immune complex. The streptavidin magnetic particles (MPs) served as the solid phase and the separator. The relevant parameters involved in the immunoassay, including the immunoassay reagents used and the physicochemical parameters were optimized. Then, urine samples from 130 patients with bladder cancer and 113 healthy controls were detected, and analyzed using the established method. The method was linear to 1,000 ng/ml survivin with a detection limit of 0.83 ng/ml. The intra- and inter-assay coefficients of variation were <8, and <11%, respectively. The concentration of diluted survivin and the dilution ratios gave a linear correlation of 0.9989. The results demonstrated that the urinary survivin levels in patients with bladder cancer were significantly higher (P<0.001) compared with that in healthy controls. At a survivin concentration of 2.0884 ng/ml, the sensitivity and specificity were 86.9 and 61.9%, respectively. Furthermore, the urinary survivin levels were positively correlated with metastatic stage, histological stage and recurrence (P<0.01). In conclusion, the present study preliminarily proposed a microplate magnetic CLIA for survivin detection and further evaluated the value of urinary survivin as a diagnostic marker for bladder cancer.

Circulating antigen tests and urine reagent strips for diagnosis of active schistosomiasis in endemic areas

BACKGROUND

Point-of-care (POC) tests for diagnosing schistosomiasis include tests based on circulating antigen detection and urine reagent strip tests. If they had sufficient diagnostic accuracy they could replace conventional microscopy as they provide a quicker answer and are easier to use.

OBJECTIVES

To summarise the diagnostic accuracy of: a) urine reagent strip tests in detecting active Schistosoma haematobium infection, with microscopy as the reference standard; and b) circulating antigen tests for detecting active Schistosoma infection in geographical regions endemic for Schistosoma mansoni or S. haematobium or both, with microscopy as the reference standard.

SEARCH METHODS

We searched the electronic databases MEDLINE, EMBASE, BIOSIS, MEDION, and Health Technology Assessment (HTA) without language restriction up to 30 June 2014.

SELECTION CRITERIA

We included studies that used microscopy as the reference standard: for S. haematobium, microscopy of urine prepared by filtration, centrifugation, or sedimentation methods; and for S. mansoni, microscopy of stool by Kato-Katz thick smear. We included studies on participants residing in endemic areas only.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data, assessed quality of the data using QUADAS-2, and performed meta-analysis where appropriate. Using the variability of test thresholds, we used the hierarchical summary receiver operating characteristic (HSROC) model for all eligible tests (except the circulating cathodic antigen (CCA) POC for S. mansoni, where the bivariate random-effects model was more appropriate). We investigated heterogeneity, and carried out indirect comparisons where data were sufficient. Results for sensitivity and specificity are presented as percentages with 95% confidence intervals (CI).

MAIN RESULTS

We included 90 studies; 88 from field settings in Africa. The median S. haematobium infection prevalence was 41% (range 1% to 89%) and 36% for S. mansoni (range 8% to 95%). Study design and conduct were poorly reported against current standards. Tests for S. haematobium Urine reagent test strips versus microscopyCompared to microscopy, the detection of microhaematuria on test strips had the highest sensitivity and specificity (sensitivity 75%, 95% CI 71% to 79%; specificity 87%, 95% CI 84% to 90%; 74 studies, 102,447 participants). For proteinuria, sensitivity was 61% and specificity was 82% (82,113 participants); and for leukocyturia, sensitivity was 58% and specificity 61% (1532 participants). However, the difference in overall test accuracy between the urine reagent strips for microhaematuria and proteinuria was not found to be different when we compared separate populations (P = 0.25), or when direct comparisons within the same individuals were performed (paired studies; P = 0.21).When tests were evaluated against the higher quality reference standard (when multiple samples were analysed), sensitivity was marginally lower for microhaematuria (71% vs 75%) and for proteinuria (49% vs 61%). The specificity of these tests was comparable. Antigen assayCompared to microscopy, the CCA test showed considerable heterogeneity; meta-analytic sensitivity estimate was 39%, 95% CI 6% to 73%; specificity 78%, 95% CI 55% to 100% (four studies, 901 participants). Tests for S. mansoni Compared to microscopy, the CCA test meta-analytic estimates for detecting S. mansoni at a single threshold of trace positive were: sensitivity 89% (95% CI 86% to 92%); and specificity 55% (95% CI 46% to 65%; 15 studies, 6091 participants) Against a higher quality reference standard, the sensitivity results were comparable (89% vs 88%) but specificity was higher (66% vs 55%). For the CAA test, sensitivity ranged from 47% to 94%, and specificity from 8% to 100% (4 studies, 1583 participants).

AUTHORS' CONCLUSIONS

Among the evaluated tests for S. haematobium infection, microhaematuria correctly detected the largest proportions of infections and non-infections identified by microscopy.The CCA POC test for S. mansoni detects a very large proportion of infections identified by microscopy, but it misclassifies a large proportion of microscopy negatives as positives in endemic areas with a moderate to high prevalence of infection, possibly because the test is potentially more sensitive than microscopy.

The affinity of magnetic microspheres for Schistosoma eggs

Schistosomiasis is a chronic parasitic disease of humans, with two species primarily causing the intestinal infection: Schistosoma mansoni and Schistosoma japonicum. Traditionally, diagnosis of schistosomiasis is achieved through direct visualisation of eggs in faeces using techniques that lack the sensitivity required to detect all infections, especially in areas of low endemicity. A recently developed method termed Helmintex™ is a very sensitive technique for detection of Schistosoma eggs and exhibits 100% sensitivity at 1.3 eggs per gram of faeces, enough to detect even low-level infections. The Helminthex™ method is based on the interaction of magnetic microspheres and schistosome eggs. Further understanding the underlying egg-microsphere interactions would enable a targeted optimisation of egg-particle binding and may thus enable a significant improvement of the Helmintex™ method and diagnostic sensitivity in areas with low infection rates. We investigated the magnetic properties of S. mansoni and S. japonicum eggs and their interactions with microspheres with different magnetic properties and surface functionalization. Eggs of both species exhibited higher binding affinity to the magnetic microspheres than the non-magnetic microspheres. Binding efficiency was further enhanced if the particles were coated with streptavidin. Schistosoma japonicum eggs bound more microspheres compared with S. mansoni. However, distinct differences within eggs of each species were also observed when the distribution of the number of microspheres bound per egg was modelled with double Poisson distributions. Using this approach, both S. japonicum and S. mansoni eggs fell into two groups, one having greater affinity for magnetic microspheres than the other, indicating that not all eggs of a species exhibit the same binding affinity. Our observations suggest that interaction between the microspheres and eggs is more likely to be related to surface charge-based electrostatic interactions between eggs and magnetic iron oxide rather than through a direct magnetic interaction.

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.

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.

Magnetic affinity enzyme-linked immunoassay for diagnosis of Schistosomiasis japonicum in persons with low-intensity infection

Most schistosome-endemic areas in China are characterized by low-intensity infections that are independent of prevalence. To establish an effective diagnostic method, we developed a magnetic affinity enzyme-linked immunoassay based on soluble egg antigens (SEA-MEIA) for diagnosing schistosomiasis in persons with low-intensity infection with Schistosoma japonicum by comparing it with a conventional enzyme-linked immunosorbent assay (ELISA). Our results showed that the SEA-MEIA had a higher sensitivity and greater precision in the diagnosis of low-intensity S. japonicum infections than the ELISA. In addition, when we used Pearson's correlation in associating SEA-MEIA with ELISA, a significant correlation existed between the two assays (r = 0.845, P < 0.001). Our data indicated that SEA-MEIA, with a higher sensitivity and greater ease of performance, would be valuable for diagnosis of schistosomiasis japonicum in persons with low-intensity infections.

Evaluation of an IgY-based immunomagnetic enzyme-linked immunosorbent assay system for detection of circulating Schistosoma japonicum antigen in serum samples from patients in China

We have developed a novel egg yolk antibody (IgY)-coated magnetic beads antigen-capture immunoassay for detection of a circulating antigen of Schistosoma japonicum in serum samples of patients in schistosomiasis-endemic areas of China. This IgY-based immunomagnetic bead enzyme-linked immunosorbent assay (IgY-IMB-ELISA) uses polyclonal IgY-coated magnetic beads as a capture antibody, and a monoclonal IgG as a detection antibody. The sensitivity of the magnetic immunoassay was 100% (40 of 40) in cases of acute infection and 91.5% (107 of 117) in chronic cases of schistosomiasis, and no positive reaction was found in 0 of 49 healthy persons. Cross-reactivity was 3.3% (1 of 33) with clonorchiasis and 0% (0 of 20) with paragonimiasis. There was a significant correlation between ELISA absorbance value and egg count (eggs per gram feces) and a correlation coefficient of 0.88 in a small sample of 14 patients. The results demonstrated that the IgY-IMB-ELISA is a sensitive and specific assay for detection of human schistosomiasis japonica.

Flow-orthogonal bead oscillation in a microfluidic chip with a magnetic anisotropic flux-guide array

A new concept for the manipulation of superparamagnetic beads inside a microfluidic chip is presented in this paper. The concept allows for bead actuation orthogonal to the flow direction inside a microchannel. Basic manipulation functionalities were studied by means of finite element simulations and results were oval-shaped steady state oscillations with bead velocities up to 500 μm/s. The width of the trajectory could be controlled by prescribing external field rotation. Successful verification experiments were performed on a prototype chip fabricated with excimer laser ablation in polycarbonate and electroforming of nickel flux-guides. Bead velocities up to 450 μm/s were measured in a 75 μm wide channel. By prescribing the currents in the external quadrupole magnet, the shape of the bead trajectory could be controlled.

Detection of circulating antigen in serum of mice infected with Schistosoma japonicum by immunomagnetic bead ELISA based on IgY

We developed a novel immunomagnetic bead ELISA based on IgY (egg yolk immunoglobulin) for detection of circulating antigen (CA) in sera of mice infected with Schistosoma japonicum. The assay involved the use of chicken polyclonal antibodies IgY against soluble egg antigens (SEA) of S. japonicum as a capture antibody and anti-SEA mouse monoclonal antibody NP28-5B labeled horseradish peroxidase (HRP) as a detecting antibody. Two groups of BALB/c mice infected with S. japonicum cercariae were used: lightly infected mice (infected with 10 S. japonicum cercariae) and heavily infected mice (infected with 30 S. japonicum cercariae). The CA was detectable as early as 4 and 5 weeks after infection in the sera of heavily and lightly infected mice, respectively. The CA levels rose rapidly and reached a peak in 8 weeks after infection and then remained a plateau for at least another 6 weeks in both groups. Moreover, the effect of praziquantel on the CA levels was also investigated. The heavily infected mice were treated with praziquantel and the CA levels in sera increased dramatically in the first week post-treatment and then decreased to the control level by 6 weeks after treatment. The novel assay appears to be sensitive for detection of schistosomal antigenemia and valuable to judge the efficacy of chemotherapy in murine schistosomiasis.

Detection of Schistosoma mansoni eggs in feces through their interaction with paramagnetic beads in a magnetic field

Background

Diagnosis of intestinal schistosomiasis in low endemic areas is a problem because often control measures have reduced egg burdens in feces to below the detection limits of classical coproparasitological methods. Evaluation of molecular methods is hindered by the absence of an established standard with maximum sensitivity and specificity. One strategy to optimize method performance, where eggs are rare events, is to examine large amounts of feces. A novel diagnostic method for isolation of Schistosoma mansoni eggs in feces, and an initial evaluation of its performance is reported here.

Methodology/Principal Findings

Known amounts of S. mansoni eggs were seeded into 30 g of normal human feces and subjected to a sequence of spontaneous sedimentation, sieving, Ritchie method, incubation and isolation through interaction with paramagnetic beads. Preliminary tests demonstrated the efficacy of lectins as ligands, but they also indicated that the paramagnetic beads alone were sufficient to isolate the eggs under a magnetic field through an unknown mechanism. Eggs were identified by microscopic inspection, with a sensitivity of 100% at 1.3 eggs per gram of feces (epg). Sensitivity gradually decreased to 25% at a concentration of 0.1 epg. In a preliminary application of the new method to the investigation of a recently established focus in southern Brazil, approximately 3 times more eggs were detected than with the thick-smear Kato-Katz method.

Conclusions/Significance

The novel S. mansoni detection method may significantly improve diagnosis of infections with low burdens in areas of recent introduction of the parasite, areas under successful control of transmission, or in infected travelers. It may also improve the evaluation of new treatments and vaccines.

Schistosomiasis mansoni is a parasitic infection that affects approximately 200 million people, mainly in the tropics. The worms live inside the veins of intestines and liver and produce eggs that are eliminated within feces. If the eggs reach water, a ciliated larva is released and enters snails to develop into a larva infective to man and other vertebrates. Most infections evolve without overt disease, but severe intestinal, hepatic, pulmonary and cerebro-medulary dysfunctions may occur after many years. Definitive diagnosis is made through the identification of eggs in stool. Classical diagnostic methods fail to detect infection when the number of eggs is low (e.g., in areas where control measures have decreased the intensity of infection or in the case of light infections in travelers who have had only brief exposure). A new and very sensitive method is reported here, in which eggs are isolated from large amounts of feces through their interaction with magnetic beads. After incubation with the fecal sediment, eggs co-migrate with the beads towards a magnet attached to the test tube. This improvement in diagnostic methodology will strengthen efforts to control schistosomiasis.

A novel magnetic bead bioassay platform using a microchip-based sensor for infectious disease diagnosis

New technologies are greatly needed to improve laboratory tests that can be used in point-of-care clinical settings. Here, a biosensor was used to detect micron-scale paramagnetic beads in order to replace the conventional enzymatic label used in ELISAs. This novel biosensor was fabricated through standard complementary metal oxide semiconductor (CMOS) manufacturing and was used to quantify magnetic beads bound to the sensor surface by immunological recognition, analogous to ELISA. CMOS technology can integrate multiple laboratory functions into the sensor chip, potentially enabling inexpensive, compact and sophisticated diagnostic systems for a number of diseases. We present results for two immunological assays: antigen capture of purified mouse IgG and detection of human anti-dengue virus IgG in clinical serum samples. The sensitivity of detecting purified protein with magnetic beads was comparable to ELISA. We found a high correlation between the ELISA optical density and the biosensor output in the clinical assay. We also demonstrate the use of a controlled magnetic field to remove non-specifically bound magnetic beads from the sensor surface, effectively washing the sensor surface. This novel sensor can be mass-produced at low cost and can detect magnetic beads bound to the surface through specific antibody-antigen interactions, making it a potential platform for new simplified and rapid point-of-care diagnostic tests.

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.

Methods for detection of Clostridium botulinum toxin in foods

Botulism is a deadly disease caused by ingestion of the preformed neurotoxin produced from the anaerobic spore-forming bacteria Clostridium botulinum. Botulinum neurotoxins are the most poisonous toxins known and have been a concern in the food industry for a long time. Therefore, rapid identification of botulinum neurotoxin using molecular and biochemical techniques is an essential component in the establishment of coordinated laboratory response systems and is the focus of current research and development. Because of the extreme toxicity of botulinum neurotoxin, some confirmatory testing with the mouse bioassay is still necessary, but rapid methods capable of screening large numbers of samples are also needed. This review is focused on the development of several detection methods for botulinum neurotoxins in foods.

Heterogeneous post-column immunoreaction detection using magnetized beads and a laboratory-constructed electromagnetic separator

The nature of immune reactors allows development of quantitative analytical methods that are highly selective and can often be used directly with complex biological matrixes such as blood, plasma or urine. A major limitation of immunoassay is that antibodies are sometimes unable to discriminate structurally similar species such as drug metabolites and synthetic analogs. The problem associated with the lack of discrimination can be circumvented by coupling immunoassay with liquid chromatography post-column. The most commonly used separation method in post-column immunoreaction detection is the affinity column. Affinity columns may create undesired effects such as a compromise of the chromatographic separation efficiency, the requirement for an antibody with fast reaction kinetics and the need for flushing the column. This paper reports a post-column immunoreaction detection system coupled with a laboratory-constructed on-line magnetic separation flow chamber that is designed to overcome these problems. The system uses disposable magnetic beads as a solid-phase support for separation that can be easily removed from the system. The model analytes chosen for this study were digoxin and its metabolites due to the commercial availability of monoclonal antibodies for these compounds. Digoxin was separated using a chromatographic method prior to being interfaced through a liquid handler system to the immunoreactor. Compatibility of the HPLC mobile phase was determined to be acceptable with a mixing ratio of 1:3 between the LC fraction and immunoreagent solution. The dynamic range of the calibration curve in digoxin-spiked phosphate buffer was found to be 0.25-12 ng/ml and a quadratic fit was found to provide the best fit to the data with a correlation coefficient of 0.9974. The residual error for all standards was less than 15%. The percentage RSDs for the two controls, 2 and 10 ng/ml, were 6.88 and 4.82% (n = 6) and the percentage errors were 7.07 and -6.89% (n = 6), respectively.

Magnetic-bead enzyme-linked immunosorbent assay verifies adsorption of ligand and epitope accessibility

Antigen- and antibody-coated magnetic beads, which are commercially available as activated particles and are readily coated with a variety of molecules, are excellent devices for selecting specific cell populations. We describe an enzyme-linked immunosorbent assay (ELISA)-based method that validates the adsorption of ligand to magnetic beads and verifies the surface accessibility of specific epitopes of the particular ligand. Accordingly, various ligands at a wide range of concentrations were incubated with magnetic beads and adsorption was then assessed using either a specific primary antibody and a secondary alkaline phosphatase-conjugated antibody or a specific primary alkaline phosphatase-conjugated antibody. The method is straightforward and fast and, due to the very low nonspecific background binding, it requires extremely small amounts of beads and ligand. It can be easily performed on newly prepared beads before using them for selection. Magnetic-bead ELISA also confirms the accessibility of specific epitopes on the surface of the beads, which corresponds to the primary antibody used in the assay.

Immunodiagnosis of schistosomiasis by determination of the circulating antigens CAA and CCA, in particular in individuals with recent or light infections

In the present paper, we evaluate determination of circulating anodic (CAA) and cathodic (CCA) antigen for the diagnosis of an active Schistosoma infection in humans, in comparison to the diagnostic performance of parasitological examination and the demonstration of specific antibodies. Illustrated by three different studies, which all deal with the diagnosis of either recent or low intensity infections, we further discuss our experiences with these diagnostic methods. For the diagnosis of recent infections, specific antibody determination showed to be very sensitive, particularly in individuals originating from non-endemic areas. For the assessment of cure and for the diagnosis of active infections in endemic areas, the methods of choice are parasitological examination and CAA or CCA determination. Depending on infection levels of the target population and on logistic conditions, CAA and CCA determination may either replace parasitological examination or, in the case of light infections, may be used as a complementary diagnostic tool.

Rapid detection of a Schistosoma mansoni circulating antigen excreted in urine of infected individuals by using a monoclonal antibody

Schistosoma circulating antigens were used to indicate the infection intensity and to assess cure. An immunoglobulin G2a (IgG2a) mouse monoclonal antibody was used in a fast dot-enzyme-linked immunosorbent assay (ELISA; FDA) for rapid and simple diagnosis of schistosomiasis in the field. Seven hundred Egyptians were parasitologically examined for Schistosoma mansoni and other parasitic infections. A rectal biopsy was done as a "gold standard" for individuals showing no S. mansoni eggs in their feces. Egg counts were obtained by the Kato smear method for only 100 of 152 individuals with eggs in their feces. Specific anti-schistosome IgG antibodies were evaluated in sera by ELISA. Urine samples from the 700 individuals were tested by FDA for detection of the circulating antigen. The assay showed a sensitivity of 93% among 433 infected individuals and a specificity of 89% among 267 noninfected individuals. FDA showed the highest efficiency of antigen detection (91%) compared with the efficiency of antibody detection by ELISA (75%) and stool analysis (60%). In addition, FDA detected infected patients with 20 eggs/g of feces. Also, the sensitivity of FDA ranged from 90 to 94% among samples from patients with different clinical stages of schistosomiasis. All the assay steps can be completed within 30 min at room temperature for 96 urine samples. The monoclonal antibody identified a 74-kDa antigen in different antigenic extracts of S. mansoni and Schistosoma haematobium and in the urine of infected individuals. In addition, a 30-kDa degradation product was identified only in the urine samples. On the basis of these results, FDA should be used as a rapid tool for the sensitive and specific diagnosis of Schistosoma infection.

Rapid detection of a Schistosoma mansoni circulating antigen excreted in urine of infected individuals by using a monoclonal antibody

Schistosoma circulating antigens were used to indicate the infection intensity and to assess cure. An immunoglobulin G2a (IgG2a) mouse monoclonal antibody was used in a fast dot-enzyme-linked immunosorbent assay (ELISA; FDA) for rapid and simple diagnosis of schistosomiasis in the field. Seven hundred Egyptians were parasitologically examined for Schistosoma mansoni and other parasitic infections. A rectal biopsy was done as a "gold standard" for individuals showing no S. mansoni eggs in their feces. Egg counts were obtained by the Kato smear method for only 100 of 152 individuals with eggs in their feces. Specific anti-schistosome IgG antibodies were evaluated in sera by ELISA. Urine samples from the 700 individuals were tested by FDA for detection of the circulating antigen. The assay showed a sensitivity of 93% among 433 infected individuals and a specificity of 89% among 267 noninfected individuals. FDA showed the highest efficiency of antigen detection (91%) compared with the efficiency of antibody detection by ELISA (75%) and stool analysis (60%). In addition, FDA detected infected patients with 20 eggs/g of feces. Also, the sensitivity of FDA ranged from 90 to 94% among samples from patients with different clinical stages of schistosomiasis. All the assay steps can be completed within 30 min at room temperature for 96 urine samples. The monoclonal antibody identified a 74-kDa antigen in different antigenic extracts of S. mansoni and Schistosoma haematobium and in the urine of infected individuals. In addition, a 30-kDa degradation product was identified only in the urine samples. On the basis of these results, FDA should be used as a rapid tool for the sensitive and specific diagnosis of Schistosoma infection.

Comparative studies of magnetic particle-based solid phase fluorogenic and electrochemiluminescent immunoassay

Two solid phase immunoassays, an electrochemiluminescent immunoassay (ECLIA) and a magnetic particle fluorogenic immunoassay (MPFIA) were evaluated and compared for bacterial detection. Briefly, the ECLIA is based on a redox reaction between ruthenium (II)-trisbipyridyl Ru[(bpy)3]2+ labeled antibody and the excess of tripropylamine, which generates photons. The entire reaction is carried on the near surface area between the spherical magnetic beads and an anode electrode. The detectable bacterial spores are at a linear range from 5 x 10(3) to 5 x 10(5) colony forming units (cfu) of Bacillus subtilis var. niger spores, 10(2) to 10(4) cfu of Bacillus anthrax spores and 10(2) to 10(6) cells of Escherichia coli O157:H7 in ECLIA. The unique MPFIA technique employs antibody-coated magnetic beads as solid phase in suspension for bacterial capture and concentration in a 96-well microplate format. Primary capturing antibodies, bacteria form a sandwich with alkaline phosphatase (AP)-labeled antibodies as reporter followed by a reaction with the AP substrate, AttoPhos to generate fluorescence for detection. Immunomagnetic separation permits direct isolating and concentrating bacterial cells from the crude samples, such as blood and environmental water. The results of MPFIA for detecting bacteria showed less sensitivity compared with that of ECLIA, however it provides a means for direct, high throughput screening bacteria from crude biological samples. Both ECLIA and MPFIA are rapid (less than one hour) and easy to use.

Schistosomiasis

Schistosomiasis is a man-made disease related to water contact in the agricultural fields and affecting millions of people in developing countries in the tropical and subtropical parts of Africa, Asia and South America. It is a bisexual trematode living in the portal blood and perivesical venous plexus. Its life cycle necessitates the presence of an intermediate host - a fresh water mollusc - that differs according to place. The pathogenetic stage is the ova that initiate an immunologically delayed hypersensitivity cell-mediated reaction in the organs where they are deposited. The liver, colon, urinary bladder and ureter are the main organs affected; however, any organ can be affected, even the skin and the brain. The review discusses the pathogenesis, pathology, diagnosis: parasitological and immunological, the clinical picture, treatment and control. The present status of the research work on vaccination is also presented.

Development of a magnetic microplate chemifluorimmunoassay for rapid detection of bacteria and toxin in blood

A magnetic microplate chemifluorimmunoassay (MMCIA) is described using an immunomagnetic separation and a fluorescent microplate technique for rapid detection of low-level Escherichia coli O157:H7, Bacillus subtilis var. niger spores, and Staphylococcal enterotoxin type B from whole blood. In general, the MMCIA has at least several-fold more sensitivity than the conventional enzyme-linked immunosorbent assay. In addition, the assay sensitivities using direct fluorochrome label as the reporter, or alkaline phosphatase (AP) with various assay substrates, such as pNPP and AttoPhos, were assessed.

Enhanced detection of Schistosoma circulating antigens by testing 1 ml urine samples using immunomagnetic beads

The potential advantage of increasing the sample volume for enhanced detection of two Schistosoma circulating antigens in urine has been evaluated. Two different, monoclonal antibody based, immunomagnetic beads assays detecting circulating anodic antigen (CAA) and circulating soluble egg antigen (CSEA), respectively, were investigated. By increasing the sample volume to 1.0 ml, the lower detection limit of antigen dilution series was improved six eight-fold in both immunomagnetic beads assays. Indeed, an improvement could be shown when testing the urine of Schistosoma-infected individuals with these magnetic beads assays. To compare the sensitivity of the immunomagnetic beads method with the standard ELISA, urine was experimentally adjusted to mirror low natural infection intensities. CSEA-positive urine samples were adjusted to levels below the detection limit of the corresponding ELISA and indeed were still found positive by the CSEA immunomagnetic beads assay. These results demonstrate that by using immunomagnetic beads, an assay method which can utilise larger sample volumes than an ELISA, enhanced detection can be achieved. This might be particularly valuable in areas with low prevalence of schistosomiasis or for the assessment of cure after chemotherapy.

Schistosomiasis. Pathophysiology, diagnosis, and treatment

Globally, schistosomes infect 1 in 30 people. Tourists travel to endemic areas, whereas students, workers, and expatriates travel to nonendemic areas. Physicians around the world need to remain aware of this common parasitic infection. Pathology results from parasite eggs that lodge in the intestines and liver. Intestinal schistosomiasis is most often asymptomatic and presents with occult gastrointestinal bleeding. Hepatosplenic schistosomiasis develops insidiously because of cumulative fibrotic injury. Stigmata of liver failure are absent unless comorbid viral or alcoholic hepatitis is present. Patients with end-stage hepatosplenic schistosomiasis die from variceal hemorrhage. Diagnosis of schistosomiasis is confirmed by finding eggs in stool or biopsy specimens. Antischistosome antibodies may identify infected tourists returning from endemic areas. Circulating schistosome antigens distinguish current from past infections. Praziquantel is the schistosomicidal drug of choice. Most cases of hepatosplenic schistosomiasis resolve after effective treatment. Prophylactic propranolol may prevent hemorrhage in praziquantel-treated patients with high-grade varices. Sclerotherapy is also efficacious. When necessary, patients with hepatosplenic schistosomiasis tolerate decompressive surgery well.

Magnetic bead protamine-linked microtiter assay for detection of heparin using iodinated low-molecular-mass heparin-tyramine

We have developed a competitive heparin binding assay employing protamine-coated magnetic beads for detection and measurement of heparin. The assay utilizes 125-iodine specifically bound to newly synthesized low-molecular-mass (LMM) heparin-tyramine. The tracer was stable over a period of 3 weeks, as demonstrated by gel filtration chromatography. The protamine-coated beads were found to be stable over at least two months. The heparin-tyramine bead assay had in buffer a lower detection limit of 0.04 microgram/ml and in plasma of 0.23 microgram heparin/ml. 50% binding was obtained at 0.7 microgram/ml and 20% binding at 4 micrograms/ml in plasma. The within assay coefficient of variation ranged from 9 to 28% for unfractionated, high molecular mass (HMM) heparin and from 12 to 15% for LMM-heparins in buffer system and in plasma. Various heparin fractions displaced the tracer from the protamine-coated magnetic beads to different extents. The validity of the assay was proven after intravenous administration of unfractionated and LMM-heparin in man. The elimination rate was similar using the heparin-tyramine bead assay compared with the anti-factor Xa coagulation assay. After intravenous dosing of LMM-heparin the maximal concentration was lower using the heparin-tyramine bead assay compared with the anti-factor Xa coagulation assay. The bead assay was found to be reproducible, valid, and rapid for measurement of the concentration of heparin preparations in purified systems and for HMM-heparin in plasma. Measurement of the concentration of LMM-heparin in plasma has a high coefficient of variation using the binding assay.

Optimization of the Magnetic Bead Antigen Capture Enzyme Immuno Assay for the detection of circulating anodic antigens in mixed Schistosoma infections

In the present study, simplification and adaptation of the Magnetic Bead Antigen Capture Enzyme Immuno Assay (MBAC-EIA) technique for detection of circulating anodic antigens (CAA) under field conditions was achieved. It was shown that the assay could be performed successfully within the broad temperature range of 18-37 degrees C. The slightly lower sensitivity observed at low temperatures could be adjusted for by prolonging the incubation period. Shaking the plate by hand was as good as automatic mechanical shaking, aspiration of the supernatant before the addition of conjugate was not necessary, and the use of whole blood and serum offered similar assay sensitivity. Furthermore incubation times could be considerably shortened without loss of sensitivity. A major advantage of the MBAC-EIA was that the beads, after elution of bound components, were found to be reusable. The study also showed that the sensitivity of the MBAC-EIA technique in diagnosis of schistosomiasis in a Zimbabwean community endemic for both urinary and intestinal schistosomiasis, was 94%.

Verification of ELISA results by immunomagnetic isolation of antigens from extracts and analysis with SDS-PAGE and western blotting, demonstrated for Erwinia spp. in potatoes

Isolation of antigens on immunomagnetic beads and subsequent analysis with SDS-PAGE and Western blotting (immunomagnetic isolation-Western blotting (IMI-WB)) was used to verify positive ELISA results for Erwinia chrysanthemi and Erw. carotovora subsp. atroseptica in potato peel extracts. Direct analysis of highly contaminated extracts by Western blotting without previous immuno-isolation resulted in background reactions, whereas immunomagnetic isolation resulted in distinct bands of specific antigens. Target cells as well as antigenic cell products were captured in IMI-WB. Band patterns on IMI-WB of cell-free culture filtrates and cell suspensions were highly similar, but the removal of cells lowered the detection level by 10- to 100-fold. Threshold levels of IMI-WB were generally comparable with those of ELISA. No differences in threshold levels and band patterns were found between a direct format and an indirect format of immuno-isolation. In IMI-WB, blotting patterns differed between Erw. chrysanthemi and Erw. carotovora subsp. atroseptica. The patterns were identical for 15 Erw. chrysanthemi strains, isolated from potato peel extracts in The Netherlands. However, one of 15 strains of Erw, carotovora subsp. atroseptica from potato peel extracts in The Netherlands gave an aberrant pattern. Target bacteria could be easily distinguished from those of cross-reacting strains on the basis of band patterns. Potato peel extracts naturally contaminated with Erw. chrysanthemi gave IMI-WB patterns that were similar to pure cultures of the homologous strains.

Magnetic separation techniques in diagnostic microbiology

The principles of magnetic separation aided by antibodies or other specific binding molecules have been used for isolation of specific viable whole organisms, antigens, or nucleic acids. Whereas growth on selective media may be helpful in isolation of a certain bacterial species, immunomagnetic separation (IMS) technology can isolate strains possessing specific and characteristic surface antigens. Further separation, cultivation, and identification of the isolate can be performed by traditional biochemical, immunologic, or molecular methods. PCR can be used for amplification and identification of genes of diagnostic importance for a target organism. The combination of IMS and PCR reduces the assay time to several hours while increasing both specificity and sensitivity. Use of streptavidin-coated magnetic beads for separation of amplified DNA fragments, containing both biotin and a signal molecule, has allowed for the conversion of the traditional PCR into an easy-to-read microtiter plate format. The bead-bound PCR amplicons can also easily be sequenced in an automated DNA sequencer. The latter technique makes it possible to obtain sequence data of 300 to 600 bases from 20 to 30 strains, starting with clinical samples, within 12 to 24 h. Sequence data can be used for both diagnostic and epidemiologic purposes. IMS has been demonstrated to be a useful method in diagnostic microbiology. Most recent publications describe IMS as a method for enhancing the specificity and sensitivity of other detection systems, such as PCR, and providing considerable savings in time compared with traditional diagnostic systems. The relevance to clinical diagnosis has, however, not yet been fully established for all of these new test principles. In the case of PCR, for example, the presence of specific DNA in a food sample does not demonstrate the presence of a live organism capable of inducing a disease. However, all tests offering increased sensitivity and specificity of detection, combined with reduced time of analysis, have to be seriously evaluated.

Comparison of immunomagnetic beads coated with protein A, protein G, or goat anti-mouse immunoglobulins. Applications in enzyme immunoassays and immunomagnetic separations

Immunomagnetic beads were prepared using either protein A (PA) or protein G (PG) coupled to magnetic beads for binding antibodies at their Fc region. The performance of these beads was compared with commercially available beads coated with goat anti-mouse (G alpha M) immunoglobulins. Both the PA- and PG-beads possessed a higher binding capacity than the G alpha M-beads for the monoclonal antibodies tested, although, PA bound weakly with some IgG1 antibodies. PA-beads were compared with G alpha M-beads in a magnetic enzyme immunoassay for the detection of mouse immunoglobulins as an alternative to a conventional capture ELISA. The magnetic enzyme immunoassay was characterized by a detection time of less than 60 min and a linear assay range from 5-10 to 500 ng/ml for G alpha M-beads and 5-10 to 1000 ng/ml for PA-beads. The capture ELISA was linear from 10 to 250 ng/ml. For immunomagnetic separation of Salmonella with immunomagnetic beads, PA-beads were superior to both PG- and G alpha M-beads. For specific isolation of bacteria from heterogeneous suspensions by immunomagnetic separation, PA- and PG-beads are preferable since G alpha M-beads crossreact with bacteria possessing proteins with Fc-binding activity.

Diagnostic techniques in schistosomiasis control. A review

Diagnosis is central to all aspects of schistosomiasis. Decisions on individual and community treatment, estimations on prognosis and assessment of morbidity, evaluation of chemotherapy and control measures all require the results from diagnostic tests. Unfortunately, all presently available techniques are characterised by diagnostic imperfections. Selection and application of methods should therefore correspond to the type of information sought by the public health officer or the epidemiologist and interpretation of test results must take into consideration the drawbacks and constraints inherent to each of the various diagnostic approaches.

Quantitative detection of schistosomal circulating anodic antigen by a magnetic bead antigen capture enzyme-linked immunosorbent assay (MBAC-EIA) before and after mass chemotherapy

The magnetic bead antigen capture enzyme-linked immunosorbent assay (MBAC-EIA) has been applied to detect schistosomal circulating anodic antigen (CAA) in pre- and post-treatment sera from 55 individuals in a Schistosoma mansoni control project in the Blue Nile valley of western Ethiopia. The amounts of CAA detected by this assay were positively correlated with the numbers of eggs per gram of faeces (epg). A significant reduction in CAA levels as measured by the MBAC-EIA was observed after mass chemotherapy. The sensitivity was 88-89% in clinically significant cases excreting more than 100 epg. In light infections, however, the sensitivity was lower. None of 32 uninfected Norwegian blood donors or 12 Ethiopian immigrants to Norway were positive. The specificity was thus estimated to be 100%. The test is rapid (1-2 h) and simple to perform without sophisticated equipment and could therefore, with slight modification, be used as a reliable method of diagnosis at field level in endemic areas undergoing mass chemotherapy campaigns or population surveys.

Early detection of circulating anodic antigen (CAA) in a case of acute schistosomiasis mansoni with Katayama fever

A 34-year-old male developed acute Katayama fever with fever, diarrhoea, joint pains, headache, urticarial rash and eosinophilia 18 days after falling into and spending 15 min in the water during water-skiing in the outlet of the Volta river. Low anti-schistosomal antibody titres were found by the immunofluorescence assay after 4 weeks, and the first Schistosoma mansoni eggs were found in faeces after 6 weeks. Both symptoms and eosinophilia increased the first days after treatment with oxamniquine, after which he improved gradually. Examination of frozen sera by the newly developed Magnetic Beads Antigen Capture-EIA (MBAC-EIA) later demonstrated a peak in schistosomal circulating anodic antigen (CAA) levels of diagnostic significance already 4 weeks after he was infected.