A MAb-based ELISA for detecting circulating antigen in CSF of patients with neurocysticercosis

Diagnostic Testing of Neurologic Infections

Neuroinfectious diseases continue to cause morbidity and mortality worldwide, with many emerging or reemerging infections resulting in neurologic sequelae. Careful clinical evaluation coupled with appropriate laboratory investigations still forms the bedrock for making the correct etiologic diagnosis and implementing appropriate management. The treating physician needs to understand the individual test characteristics of each of the many conventional candidate-based diagnostics: culture, pathogen-specific polymerase chain reaction, antigen, antibody tests, used to diagnose the whole array of neuroinvasive infections. In addition, there is a growing need for more comprehensive, agnostic testing modalities that can identify a diversity of infections with a single assay.

Comparative profile of circulating antigenic peptides in CSF, serum & urine from patients with neurocysticercosis diagnosed by immunoblotting

Traditionally serum and/or CSF specimens have been used for detection of either specific antibodies or antigens as a supportive diagnosis of NCC. However, in recent days, much interest has been shown employing noninvasive specimens such as urine. In our study, we identified and compared a profile of circulating antigenic peptides of parasite origin in three different body fluids (CSF, serum and urine) obtained from confirmed NCC cases and control subjects. The circulating antigenic peptides were resolved by SDS-PAGE and subjected to immunoblotting. For confirmation of their origin as parasite somatic or excretory secretory (ES) material, immunoreactivity was tested employing affinity purified polyclonal Taenia solium metacestode anti-somatic or ES antibodies, respectively. Only lower molecular weight antigenic peptides were found circulating in urine in contrast to serum and CSF specimens. Few somatic peptides were identified to be 100% specific for NCC (19·5 kDa in all three specimens; 131, 70 kDa in CSF and serum only; 128 kDa in CSF only). Similarly, the specific ES peptides detected were 32 kDa (in all three specimens), 16·5 kDa (in serum and CSF only), and 15 kDa (urine only). A test format detecting either one or more of these specific peptides would enhance the sensitivity in diagnosis of NCC.

A rapid slide agglutination test for the diagnosis of neurocysticercosis in the rural health set up

Background:

Simple and rapid latex-based diagnostic tests have been used for detecting specific antigens or antibodies in several diseases.

Aims:

The aim of the present study was to standardize and evaluate the latex agglutination test (LAT) for the detection of Taenia solium metacestode antigen in the cerebrospinal fluid (CSF) and serum for the diagnosis of neurocysticercosis (NCC).

Settings and Design:

The study was conducted at Department of Microbiology, Jawaharlal Institute of Post graduate medical education and research after obtaining informed consent from the study subjects.

Materials and Methods:

In the present study, CSF and serum samples were collected from clinically suspected NCC, CT/MRI proven cases of NCC, non-cysticercal central nervous system infection control and from healthy control subjects. CSF was not collected from healthy controls. Polyclonal antisera raised in rabbits against porcine T. solium metacestode complete homogenate antigen, was used in the LAT to detect the antigen in the specimens.

Statistical Analysis Used:

The statistical analysis was carried out using Epi Info. The sensitivity, specificity, positive predictive value, and negative predictive value of the LAT were calculated.

Results:

The LAT exhibited sensitivity of 64.7% and specificity of 85.7% with CSF samples and sensitivity of 52.08% and specificity of 96% with serum samples.

Conclusions:

Results of the present study shows that the LAT can be employed as a moderately sensitive and specific test for the detection of T. solium metacestode antigen in the CSF and serum specimens for the diagnosis of NCC in poorly equipped laboratories.

Immunological and molecular diagnosis of cysticercosis

Cysticercosis, the infection with the larval stage of Taenia solium, is a cause of neurological symptoms including seizures, affecting the quality of life of patients and their families. Diagnosis focuses on brain imaging and serological tests are mostly used as confirmatory tools. Most cases, however, occur in poor endemic areas, where both kinds of diagnostic tools are poorly available. Development of point of care diagnostic tests is one of the most important priorities for cysticercosis researches today. The ideal point of care test would require detection of viable cysticercosis and hopefully identify cases with severe or progressive forms of neurocysticercosis, leading to referral of the patient for specialized medical attention. This manuscript describes the evolution of the serological diagnosis of cysticercosis over time, and the characteristics of the most common currently available tools, their advantages and disadvantages, and their potential use in future diagnostic tests.

Detection of secreted cysticercal antigen: a useful tool in the diagnosis of inflammatory neurocysticercosis

Neurocysticercosis is a common parasitic disease of the human central nervous system. It is particularly prevalent in developing countries, where it has a serious public health and economic impact. A major diagnostic problem with neurocysticercosis is its pleomorphic nature. Conventional diagnosis of neurocysticercosis still requires brain-computed tomography and/or magnetic resonance imaging, which are definitive but often prohibitively expensive and inaccessible in endemic areas. Herein, the monoclonal antibody HP10 antigen-trapping enzyme-linked immunosorbent assay, which has been used successfully to detect viable Taenia solium cysticercosis, was evaluated using cerebrospinal fluid (CSF) from Mexican neurocysticercosis patients with various defined pathologies. Sensitivity was higher in cases of inflammatory compared with non-inflammatory disease (94.1% vs. 33.3%) and in cases of multiple- compared with single-cyst cysticercosis (85% vs. 33.3%). Positivity was a strong indicator of active, inflammatory, multiple-cyst neurocysticercosis detecting 100% (15/15) of such cases. The overall specificity, as determined using CSF samples from patients with other neurological symptoms, was 97.7% (42/43). Since the assay only detects viable infection, it is of known value in the follow-up of treated patients to determine whether treatment has been successful. Thus, antigen detection may be of particular value in the assessment of symptomatic patients, who may potentially benefit from rapid treatment.

Immunodiagnostic tools for human and porcine cysticercosis

The development of improved immunodiagnostic tools has contributed to our knowledge on the importance of taeniosis/cysticercosis by enabling sero-epidemiological surveys and community-based studies to be carried out. Immunodiagnostic techniques include detection methods for specific antibodies and for circulating parasite antigen in serum or cerebrospinal fluid. The antigens used in immunoblot and enzyme-linked immunosorbent assay (ELISA) for antibody detection have evolved from crude extracts to highly purified specific fractions and recombinant antigens of the glycoprotein family, increasing both the sensitivity and the specificity of the tests. The application of ELISA for the detection of circulating parasite antigens may present some diagnostic advantages since it demonstrates not only exposure but also active infections. Until now only a few of the current techniques have been standardised and fully validated, making comparisons between studies difficult. The lack of a gold standard is a serious drawback. In surveys on cysticercosis, antibody detection systems have been useful in identifying the risk factors associated with transmission of Taenia solium; a high seroprevalence in a community indicates a "hot spot" where preventive and control measures should be applied. In contrast, the potential use of immunodiagnostic tools to identify cases of neurocysticercosis (NCC) in man is subject to debate. The correlation between a positive serology and neurological symptoms and/or lesions indicative for NCC on neuro-imaging techniques is poor to fair in most studies. This may be explained by the unpredictable clinical outcome of the infection and the variable immunological response of the human host to infection. A major problem is that in many developing countries, neuro-imaging methods are inaccessible and/or too expensive for the rural population at risk. Under these conditions, serology may provide the only tool for diagnosis of the infection.

Excretory/secretory antigens (ES) from in-vitro cultures of Taenia crassiceps cysticerci, and use of an anti-ES monoclonal antibody for antigen detection in samples of cerebrospinal fluid from patients with neurocysticercosis

Antigens were obtained from cysticerci of the ORF strain of Taenia crassiceps, by culture of cysts in protein-free hybridoma medium (PFHM). Budding of new vesicles was observed after 24-48 h. Excretory/secretory (ES) antigens (peptides of <20 kDa) were recovered in the medium after culture for 48 h. SDS-PAGE analysis of vesicular-fluid (VF) antigens (obtained by rupturing T. crassiceps cysticerci in PFHM) and the ES antigens indicated partial homology between the two preparations. ES peptides of 18- and 14-kDa were recognized by polyclonal antibodies produced in rabbits immunized either with the VF antigens or with a total-antigen preparation of T. solium cysticerci. Antibodies present in samples of serum or cerebrospinal fluid (CSF) from patients with neurocysticercosis also reacted with ES peptides. An anti-ES monoclonal antibody detected antigens in the CSF from 10 patients with neurocysticercosis, showing the antigenic homology of the ES antigens with those of T. solium cysticerci in human infections.

Cysticercus antigens in cerebrospinal fluid samples from patients with neurocysticercosis

Antigens were detected in cerebrospinal fluid (CSF) samples from patients with neurocysticercosis (NC) by enzyme-linked immunosorbent assay (ELISA) using polyclonal sera of rabbit anti-Taenia solium cysticerci (anti-Tso) and anti- Taenia crassiceps cysticerci vesicular fluid (anti-Tcra or anti-Tcra <30 kDa). A group of NC patients (n = 174) were studied (NC), including 40 patients in different phases of the disease. ELISAs carried out with the anti-Tso, anti-Tcra, and anti-Tcra <30 kDa showed sensitivities of 81.2, 90, and 95.8% and specificities of 82, 98, and 100%, respectively. The 14- and 18-kDa low-molecular-weight peptides were only detected in CSF samples from patients with NC by immunoblotting with anti-Tso and anti-Tcra sera. Because of the importance of the diagnosis and prognosis of cysticercosis, the detection of antigens may contribute as an additional marker to the study and clarification of the parasite-host relationship.

Serum antigen detection in the diagnosis, treatment, and follow-up of neurocysticercosis patients

The efficacy of albendazole (ABZ) treatment for human neurocysticercosis (NCC) was assessed by using a monoclonal antibody-based parasite antigen detection ELISA which specifically detects the products of living cysticerci in human serum. The assay displayed 85% diagnostic sensitivity, detecting 39 of 46 NCC cases. Only patients with a single viable cyst or only enhancing lesions (degenerating parasites) were seronegative. Specificity of the assay was 92% (23/25) when tested in healthy Peruvian volunteers. In 'cured' patients, in whom all parasites died after ABZ therapy, parasite antigen levels fell sharply by 3 months post treatment. This pattern was not observed in patients refractory to treatment. The sensitivity of the assay with serum samples, and its ability to identify successfully treated patients, make this monoclonal antibody-based ELISA the test of choice for the follow-up of NCC cases.

Production of monoclonal antibodies anti-Taenia crassiceps cysticerci with cross-reactivity with Taenia solium antigens

We describe the production of the potential monoclonal antibodies (MoAbs) using BALB/c mice immunized with vesicular fluid (VF)-Tcra (T. crassiceps) antigen. Immune sera presented anti-VF-Tcra (<20kD) IgG and IgM antibodies with cross-reactivity with T. solium (Tso) antigen (8-12, 14, and 18 kD). After cell fusion, we selected 33 anti-Tcra and anti-Tso reactive IgM-clones and 53 anti-Tcra specific IgG-clones, 5 of them also recognizing Tso antigens. Two clones identified the 8-14 and 18kD peptides of VF-Tcra.

A specific antigen-detection ELISA for the diagnosis of human neurocysticercosis. The Cysticercosis Working Group in Peru

An enzyme-linked immunosorbent assay (ELISA) for the detection of antigen secreted by viable Taenia solium metacestodes (Ag-ELISA) was applied to 43 pre-treatment and 47 follow-up cerebrospinal fluid (CSF) samples from Peruvian patients with neurocysticercosis demonstrated by computed tomography and enzyme-linked immunoelectrotransfer blot assay. The sensitivity of the assay was 86%. Negative pre-treatment results in the Ag-ELISA test were restricted to patients with only a single live cyst or only enhancing lesions. Patients with hydrocephalus had higher levels of circulating antigen. There was no difference between antigen levels in CSF taken before and immediately after treatment (day 14). Levels of parasite antigen were significantly positively correlated with the number of live cysts detected by tomography and were also proportional to the number and intensity of antibody reactions recognized by the immunoblot diagnostic test. In contrast, there was a negative correlation with the number of enhancing lesions revealed by tomography, supporting the hypothesis that enhancing lesions correspond to a terminal, moribund stage of the parasite. The use of antigen-detection tests specific for viable metacestodes has immediate utility in the clinical context, not only providing important information on the viability of the parasites but also leading to an improved understanding of the pathogenesis of neurocysticercosis before and after drug treatment.