Assessment of immunoglobulin-M immunosorbent agglutination assay (ISAGA) for detecting toxoplasma specific IgM

In defense of children's brain: reshuffling the laboratory toolbox for the diagnosis of congenital toxoplasmosis

For decades, an immunosorbent agglutination assay (ISAGA) has been considered the gold standard method for the detection of Toxoplasma gondii-specific IgM in infants for the diagnosis of congenital toxoplasmosis (CT). The Toxoplasma IgM ISAGA was consistently reported as having superior sensitivity. Unfortunately, the commercial kit for the detection of Toxoplasma IgM ISAGA will no longer be available in 2024 and alternatives will only be available at a handful of reference laboratories as in-house or laboratory-developed tests. In a recent study, S. Arkhis, C. Rouges, N. Dahane, H. Guegan, et al. (J Clin Microbiol 62:e01222-23, 2024, https://doi.org/10.1128/jcm.01222-23), reported that the performance of the PLATELIA Toxo IgM was comparable to that of the ISAGA method for the diagnosis of CT. A second study revealing similar results supports the PLATELIA Toxo IgM as the new gold standard for the detection of T. gondii-specific IgM in infants. Although the laboratory toolbox for CT diagnosis has been reshuffled successfully, it is by universally implementing all available serological and molecular tools at the earliest possible time during gestation that we can best defend children's brain from the potential harm caused by trans-placentally transmitted T. gondii.

Congenital Toxoplasmosis Diagnosis: Current Approaches and New Insights

PURPOSE

The aim of this study is to describe and discuss current disadvantages in congenital toxoplasmosis (CT) diagnosis, and what can be improved or changed through new perspectives and technological advances.

METHODS

We used Pubmed, Cochrane, and EBSCO databases to research publications from 10 years to date describing current diagnostic methods for CT. The keywords used for this Mini-Review were Toxoplasma gondii, congenital toxoplasmosis, diagnosis, and prospects using Boolean operators such as AND, OR, identifying scientific publications highlighting the importance of implementing new diagnostic methods.

RESULTS

Current diagnosis methods have several disadvantages, i.e., time-consuming, low sensitivity or specificity, and non-cost effective, that bring up the necessity of improving or developing new approaches. Recombinant proteins can help improve specificity by generating tests that use circulating strains in a specific geographical region, SAG1 and BAG1, as they are expressed during a particular stage of the disease (acute or chronic, respectively), for its use in serological diagnoses, such as capture ELISA and immunochromatography. Point of Care (POC) tests are methods performed at the patient care site, which leads to rapid patient treatment; despite the advantages, several improvements and perspectives are necessary to be implemented globally.

CONCLUSIONS

Although already established diagnosis methods for CT may be sufficient in some regions, there is still a persistent demand to develop tests with higher throughput, cost, and time reduction in developing countries, where prevalence is high. New approaches in CT diagnosis, such as recombinant proteins, capture ELISA, immunochromatography, and POC tests methods, can increase performance in terms of specificity and sensitivity simplifying diagnostic tests' requirements.

Relationship between Toxoplasma gondii infection and psychiatric disorders in Iran: A systematic review with meta-analysis

BACKGROUND

Toxoplasma gondii, a ubiquitous parasitic protozoan, may be an important cause of neurological and psychiatric diseases. The present systematic review and meta-analysis, therefore, was conducted to investigate the scientific evidence regarding the potential association between T. gondii infection and psychiatric disorders in Iran.

METHODS

We systematically reviewed articles from world-wide databases, including PubMed, Scopus, Science Direct, Web of Science, Google Scholar, and Iranian national databases up to July 30th, 2021. The Newcastle Ottawa Scale (NOS) was used to assess the quality of included studies. The common odds ratio (OR) was estimated using inverse variance and a random-effects model. Heterogeneity was assessed using the χ2-based Cochrane test (Q) and the I2 index. Also, sensitivity analyses and publication bias were calculated. Moreover, subgroup analysis was performed based on the type of disorder and quality score of different eligible studies.

RESULTS

16 studies were included in this meta-analysis. Our meta-analyses found that the OR of the risk of anti- T. gondii IgG and IgM in psychiatric patients compared to the control group was 1.56 (95% CI; 1.23-1.99) and 1.76 (95% CI: 1.19-2.61), respectively. Subgroup analysis based on the type of disorder showed that the OR of the risk of anti- T. gondii IgG in Iranian schizophrenia patients and other psychiatric disorders compared to the control group were 1.50 (95% CI; 1.09-2.07) and 2.03 (95% CI: 1.14-3.60), respectively, which are statistically significant. Also, the OR of the risk of anti- T. gondii IgM in Iranian schizophrenia and depression patients compared to the control group was 1.54 (95% CI; 0.9-2.64) and 1.03 (95% CI: 0.2-5.24), respectively, which are not statistically significant. Additionally, subgroup analysis based on quality scores showed no significant influence on the results according to the moderate quality studies. However, this association was significant according to the high quality studies. The obtained results of Egger's test were 1.5 (95% CI; -0.62-3.73, P = 0.15) and 0.47 (95% CI; -0.82-1.76, P = 0.45), respectively, indicating publication bias. The significant results of the heterogeneity analysis confirmed a high level of heterogeneity in the IgG test (P = 0.000, I2 = 66.6%). However, no significant results from the test of heterogeneity were detected in the IgM test (P = 0.15, I2 = 27.5%). The results of the sensitivity analysis showed that the impact of each study on the meta-analysis was not significant on overall estimates.

CONCLUSIONS

Despite the limited number of studies, these outcomes supported a possible link between T. gondii infection and psychiatric disorders in Iran. However, more high-quality investigations are needed in the future.

Sagacious epitope selection for vaccines, and both antibody-based therapeutics and diagnostics: tips from virology and oncology

The target of an antibody plays a significant role in the success of antibody-based therapeutics and diagnostics, and vaccine development. This importance is focused on the target binding site—epitope, where epitope selection as a part of design thinking beyond traditional antigen selection using whole cell or whole protein immunization can positively impact success. With purified recombinant protein production and peptide synthesis to display limited/selected epitopes, intrinsic factors that can affect the functioning of resulting antibodies can be more easily selected for. Many of these factors stem from the location of the epitope that can impact accessibility of the antibody to the epitope at a cellular or molecular level, direct inhibition of target antigen activity, conservation of function despite escape mutations, and even non-competitive inhibition sites. By incorporating novel computational methods for predicting antigen changes to model-informed drug discovery and development, superior vaccines and antibody-based therapeutics or diagnostics can be easily designed to mitigate failures. With detailed examples, this review highlights the new opportunities, factors and methods of predicting antigenic changes for consideration in sagacious epitope selection.

Performance of a Toxo IgM prototype assay for the diagnosis of maternal and congenital Toxoplasma infections

Background Testing for anti-Toxoplasma immunoglobulin (Ig)M is of main importance in the context of pregnancy to promptly alert to an acute maternal infection prior to the detection of IgG and to identify infected newborns. Their absence helps exclude a recent maternal infection in the presence of IgG. Methods The performance of a Toxo IgM immunocapture prototype assay (bioMérieux, France) was compared with that of the VIDAS® Toxo IgM and the ARCHITECT® Toxo IgM (Abbott, Germany) assays at Grenoble and Lyon (France). A total of 1446 sera were sampled from (i) 1054 pregnant women found by routine workup to have no infection (n = 843), an acute infection (<4 months) (n = 28) or a chronic infection (>4 months) with residual (n = 120) or no IgM (n = 62); (ii) 50 three-serum panels sampled immediately after a maternal seroconversion; (iii) 242 samples taken in 41 children with a congenital toxoplasmosis (n = 122) and in 40 uninfected children (n = 120). Results In pregnant women, the overall agreement with the VIDAS® assay was 99.23% (CI: 99.16-99.27) and that with the ARCHITECT® assay was 99.14% (CI: 99.07-99.17). Sensitivity of the Toxo IgM prototype assay was 100% (CI: 87.66-100.00) and specificity was 99.64% (98.96-99.93). In acute maternal infections, IgM assays were detected as early with the prototype as with the other two. In the congenitally infected children, IgM were detected on their first sample in 25/40 with the prototype vs. 23/40 with the VIDAS® test. No uninfected child had positive IgM. Conclusion The prototype performed comparably to the ARCHITECT® and VIDAS® Toxo IgM assays for the diagnosis of maternal and congenital toxoplasmosis.

Help in the Choice of Automated or Semiautomated Immunoassays for Serological Diagnosis of Toxoplasmosis: Evaluation of Nine Immunoassays by the French National Reference Center for Toxoplasmosis

Toxoplasmosis, a benign infection, is asymptomatic or paucisymptomatic in over 80% of cases, except in immunocompetent patients suffering from ocular toxoplasmosis or in immunocompromised patients with opportunistic or congenital toxoplasmosis. Diagnosis is based mainly on serology testing. Thus, we compared the performance of the nine most commonly used commercial automated or semiautomated immunoassays for IgG and IgM Toxoplasma gondii antibody detection, that is, the Advia Centaur, Architect, AxSYM, Elecsys, Enzygnost, Liaison, Platelia, VIDAS, and VIDIA assays. The assays were conducted on four panels of serum samples derived during routine testing from patients with an interfering disease and who exhibited a low IgG antibody level in one of two clinical settings, namely, acute or chronic toxoplasmosis. As a result, IgG sensitivities ranged from 97.1% to 100%, and IgG specificities ranged from 99.5% to 100%. For IgG quantification, strong differences in IgG titers (expressed in IU/ml) were noted depending on the assay used. IgM sensitivities ranged from 65% to 97.9%, and IgM specificities ranged from 92.6% to 100%. For defining the best serological strategies to be implemented, it appears crucial to compare the diagnostic performance of the different tests with respect to their specificity and sensitivity in detecting the presence of IgG and IgM antibodies.

Relevance of and New Developments in Serology for Toxoplasmosis

Toxoplasmosis is a widespread parasitic disease caused by the intracellular parasite Toxoplasma gondii with a wide spectrum of clinical outcomes. The biological diagnosis of toxoplasmosis is often difficult and of paramount importance because clinical features are not sufficient to discriminate between toxoplasmosis and other illnesses. Serological tests are the most widely used biological tools for the diagnosis of toxoplasmosis worldwide. This review focuses on the crucial role of serology in providing answers to the most important questions related to the epidemiology and diagnosis of toxoplasmosis in human pathology. Notwithstanding their undeniable importance, serological tools need to be continuously improved and the interpretation of the ensuing results remains complex in many circumstances.

Meta-Analysis of Anti-Toxoplasma gondii IgM Antibodies in Acute Psychosis

INTRODUCTION

A number of different infections are associated with acute psychosis. However, relationships between infections and acute psychosis in patients with schizophrenia have not been extensively explored. Exposure to Toxoplasma gondii is a replicated risk factor for schizophrenia. Previous studies have focused on T. gondii IgG antibodies, which are a marker of lifetime exposure, whereas IgM antibodies are a marker of acute/recent exposure, persistent infection, or reinfection. We performed a meta-analysis of T. gondii IgM antibodies and acute psychosis, to further investigate whether infections may be associated with relapse in schizophrenia.

METHODS

We identified articles by systematic searches of PubMed, PsycINFO, and ISI databases. We included studies, in English, of serum T. gondii IgM antibodies in patients with acute psychosis and controls.

RESULTS

Sixteen independent samples (2353 patients and 1707 controls) met inclusion criteria. Data were pooled using a random effects model. There was a significant increase in risk of positive T. gondii IgM antibodies in acute psychosis compared with controls (7.6% vs 5.7%, OR = 1.68, 95% CI = 1.23-2.27, P = .001). The association was stronger for patients with chronic schizophrenia (8.7% vs 4.6%, OR = 2.54, 95% CI = 1.63-3.96, P < .001) than first-episode psychosis. In meta-regression analyses, age, sex, and publication year were unrelated to the association; however, there was a significant association with geographic region.

DISCUSSION

An increased seroprevalence of T. gondii IgM in patients with acute psychosis complements and extends previous findings, suggesting that infections may be relevant to the etiopathophysiology of relapse in some patients with schizophrenia.

Laboratory support in the diagnosis of uveitis

Intraocular inflammations are still a diagnostic challenge for ophthalmologists. It is often difficult to make a precise etiological diagnosis in certain situations. Recently, there have been several advances in the investigations of uveitis, which has helped the ophthalmologists a lot in the management of such clinical conditions. A tailored approach to laboratory diagnosis of uveitic cases should be directed by the history, patient's symptoms and signs, and clinical examination. This review summarizes various modalities of laboratory investigations and their role in the diagnosis of uveitis.

Evaluation of the Roche Elecsys Toxo IgG and IgM electrochemiluminescence immunoassay for the detection of gestational Toxoplasma infection

Unidentified gestational infection with Toxoplasma gondii may lead to fetal infection with severe complications later in childhood. Because diagnosis of maternal infection solely depends on serology, routine tests with high sensitivity and specificity are required. In this study, the new Roche Elecsys Toxo IgG and IgM immunoassay was compared with Sabin-Feldman dye test and immunosorbent agglutination assay-IgM as reference test. Serum samples were analyzed from 927 pregnant women, including 100 negative, 706 chronic, and 121 acute infections. The combination of both Elecsys IgG and IgM assays demonstrated high sensitivity and specificity of 97.1% and 100.0%, respectively, and a positive and negative predictive value of 100.0% and 81.3%, respectively. The Elecsys assay is a useful tool as a first-line screening method to detect gestational infections. However, if gestational infection is assumed, confirmatory testing by a reference laboratory might be necessary to discriminate between pre- and postconceptional infection to start antiparasitic treatment to avoid mother-to-fetus transmission and severe sequelae.

Sequential recognition of antigenic markers of Toxoplasma gondii tachyzoite by pooled sera of mice with experimental toxoplasmosis

Accurate diagnosis of maternal toxoplasmosis can enhance the success of medical treatment and prevent congenital transmission. The current diagnostic methods have many limits, and they poorly differentiate between recent and latent infections. The present work was conducted to record the sequential recognition of antigenic markers of both Toxoplasma tachyzoites whole extract and glycosylinositolphospholipids (GIPLs)-enriched fraction by specific IgG and IgM, respectively, by immunoblotting analysis of the antigens against daily pooled serum samples from mice with experimentally induced recent and latent toxoplasmosis. IgG avidity immunoblotting was tested by using a wash with 6 M urea solution as antigen-antibody disrupting agent. Band of 10 kDa reacted exclusively with low-avidity IgG in pooled sera of mice with recent infection. Band of 39 kDa was a good marker for the infection; reacting with both low-avidity IgG in recent infection and with high-avidity IgG in latent one. Bands of 15, 23, 30, 60, 66, and 97 kDa reacted with variable avidity in both phases of infection. Two antigenic bands were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the GIPLs-enriched fraction of tachyzoite, the 14- and 30-kDa band. The 14-kDa band was recognized by IgM in pooled serum samples of recently infected mice only, while the 30-kDa band was recognized by serum samples of both recent and latent phases of infections. The study highlights the value of avidity immunoblotting assay to discriminate between recent and latent experimental toxoplasmosis. Further study must be carried on human to evaluate the values of the used technique.

Evaluation of the Vitros ECiQ immunodiagnostic system for detection of anti-Toxoplasma immunoglobulin G and immunoglobulin M antibodies for confirmatory testing for acute Toxoplasma gondii infection in pregnant women

Infection with Toxoplasma gondii is often asymptomatic and, when acquired during pregnancy, may lead to connatal toxoplasmosis in the offspring. The newly introduced Vitros anti-Toxoplasma immunoglobulin G (IgG) and IgM assays, designed for the Vitros ECiQ immunodiagnostic system, a fully automated system based on chemiluminescence, were evaluated as a screening method for the serological detection of acute and chronic Toxoplasma infections in the sera of 719 pregnant women. The combination of the Vitros IgG and IgM assays demonstrated a sensitivity and a specificity of 100% for the successful detection of all acute T. gondii infections by comparison with the Sabin-Feldman dye test as the reference test. The Vitros IgG assay parameter revealed a sensitivity of 95.0%, a specificity of 100.0%, a positive predictive value of 100.0%, a negative predictive value of 86.2%, and an overall agreement of 96.2% by comparison with the dye test. Comparison of the Vitros Toxoplasma IgM assay with the immunosorbent agglutination assay yielded values of 77.1%, 99.0%, 97.7%, 88.5%, and 91.1%, respectively. Subsequent receiver operating characteristic curve analysis for the accurate detection of Toxoplasma IgM in acute (n = 90) and chronic (n = 461) infections demonstrated high sensitivity (92.2%) and specificity (81.6%). The combination of a Toxoplasma-specific IgG assay with specific IgM antibody detection has improved the diagnosis of T. gondii infection by decreasing follow-up testing. Nonetheless, positive Toxoplasma IgM test results during pregnancy necessitate confirmatory testing by a reference laboratory to ensure fast and, above all, accurate test results.

Serological Screening of Newborns for Toxoplasma Gondii-Specific IgA and IgM Antibodies in Peripheral Blood Collected on Filter-Papers

The strategic approach for preventing congenital toxoplasmosis is strictly related to the incidence of primary T. gondii infection during pregnancy in a studied population. Early postnatal diagnosis by mass testing of newborns is an option in areas where obligatory serological screening in pregnant women has not been implemented but it requires sensitive immunodiagnostic methods followed by a good confirmatory analysis. The aims of the regional neonatal screening programme were (i) analysis of the prevalence of congenital T. gondii infection at birth in the West Poland Province, (ii) determination of the value of the serological examination of filter-paper blood specimens collected at birth for the diagnosis of congenital toxoplasmosis, and (iii) evaluation of the duration of T. gondii-specific immunoglobulin A and immunoglobulin M antibodies in infants' sera. The neonates born in the obstetric clinics of the University Gynaecology-Obstetrics Hospital in Poznan (Poland) and in the maternity wards of the 10 main district hospitals from the West Poland region were systematically screened for congenital T. gondii infection. Peripheral blood from newborns was collected by a non-invasive heel-stick puncture during the first 3 days of life, absorbed onto Guthrie cards and analysed for anti-T. gondii specific IgM (1996-1998) or both IgA and IgM antibodies (1998-2000) by non-commercial immunocapture ELISAs. When the screening result was positive, the diagnosis of congenital infection was confirmed by testing serum samples from the suspected neonate and the mother using a Western blot IgM-IgG comparative immunological profile analysis and traditional serological techniques (ELISA, ISAGA) for anti-Toxoplasma IgA, IgM and IgG specific antibodies. From June 1996 to April 2000, 45,169 filter-paper specimens from liveborn neonates were screened: 27,516 samples were tested for specific IgM and the next 17,653 Guthrie cards were analysed by the combined IgA/IgM assay. The prevalence of anti-Toxoplasma IgM in filter-paper eluates at birth was 1 per 2,117 liveborn neonates (0.47/1000) or 1 per 1,185 infants (0.84/1000) born to seronegative women with a potential risk of primary T. gondii infection during pregnancy. For the joint detection of IgA and IgM, these values significantly increased to 1 per 929 neonates (1.08/1000) or 1 per 520 pregnancies at risk (1.92/1000) respectively, comparing to the seropositivity rate of 43.7% in a pregnant women population in the studied area. In newborns untreated prenatally, the diagnostic sensitivity of the IgM ELISA using neonatal Guthrie cards was not more than 86.7% and that of the combined IgA/IgM ELISA was 95%; the diagnostic specificity of the both methods was calculated to be 99.9%. Congenital T. gondii infection was finally diagnosed in 35 neonates, mostly asymptomatic at birth.

CONCLUSIONS

(i) The neonatal screening for anti-Toxoplasma IgA and/or IgM antibodies is a good sensitivity method for an early postnatal diagnosis of congenital toxoplasmosis in newborns untreated prenatally. (ii) In the absence of obligatory nation-wide screening during pregnancy followed by an early prenatal treatment, this valuable technique may be considered a preventive option in areas of a high annual number of births associated with a high seroprevalence of T. gondii infection.

Usefulness of Western blot in serological follow-up of newborns suspected of congenital toxoplasmosis

The goal of the study reported here was to compare the results of Western blot with other serological methods for testing newborns suspected of having congenital toxoplasmosis. Western blot, enzyme-linked immunosorbent assay, immunoglobulin (Ig)M immunosorbent agglutination assay, and indirect immunofluorescence assay were performed on the sera of 126 neonates collected at birth and at 1 and 3 months of life. Western blot was more sensitive than IgM detection with the immunosorbent agglutination assay (82.6% vs. 69.6%), and the specificity of the two methods was 96.1% and 92.2%, respectively. Among the serological techniques tested, the combination of Western blot (IgG and IgM) with IgM immunosorbent agglutination assay achieved the greatest improvement in the sensitivity of early (postpartum) diagnosis of congenital toxoplasmosis.

Immunoglobulin M (IgM)-glycoinositolphospholipid enzyme-linked immunosorbent assay: an immunoenzymatic assay for discrimination between patients with acute toxoplasmosis and those with persistent parasite-specific IgM antibodies

In the present study we developed an enzyme-linked immunosorbent assay (ELISA) to measure immunoglobulin M (IgM) specific for glycoinositolphospholipids (GIPL) derived from tachyzoite membrane (IgM-GIPL ELISA). The sensitivity and specificity of the assay were compared with those of commercially available Toxoplasma-specific IgM serological tests, namely, immunofluorescence assay (IFA) with fixed tachyzoites and capture ELISA employing tachyzoite extracts. Our results show that all patients with acute toxoplasmosis, as determined by clinical data and conventional serological tests, were also positive by the IgM-GIPL ELISA. Interestingly, many patients that were classified as indeterminate, who had IgG with high avidity but positive results in the IgM-specific IFA and capture ELISA, were negative by the IgM-GIPL ELISA. Finally, we tested the sera from patients with rheumatoid arthritis and various parasitic infections and found no evidence of false positives in the IgM-GIPL ELISA.

Strategy for diagnosis of congenital toxoplasmosis: evaluation of methods comparing mothers and newborns and standard methods for postnatal detection of immunoglobulin G, M, and A antibodies

In a study involving 14 laboratories supported by the European Community Biomed 2 program, we evaluated immunologic methods for the postnatal diagnosis of congenital toxoplasmosis (CT). Among babies born to mothers who seroconverted to positivity for toxoplasmosis during pregnancy, we analyzed 55 babies with CT on the basis of persistent anti-Toxoplasma immunoglobulin G (IgG) at 1 year of life and 50 control babies without anti-Toxoplasma IgG at 1 year of life in the absence of curative treatment with pyrimethamine-sulfonamides. We tested in-house methods such as the enzyme-linked immunofiltration assay (ELIFA) or Immunoblotting (IB) for the detection of IgG or IgM; these methods allowed comparison of the immunologic profiles of the mothers and the infants. We compared ELIFA and IB with a commercial enzyme immunoassay (EIA) or in-house immunosorbent agglutination assay (ISAGA) for the detection of IgM or IgA. The performances of combinations of methods were also assessed. A cumulative sensitivity of 98% during a 1-year follow-up was obtained with the ELIFA plus ISAGA combination. Only one case of CT was missed by the ELIFA plus ISAGA combination, whereas three cases were missed by the IB plus ISAGA combination, even though 48% of patients with CT were treated with pyrimethamine-sulfonamides, which are known to inhibit antibody neosynthesis. A similar performance was obtained with either ELIFA or IB in combination with EIA. The difference in performance between ELIFA plus ISAGA and IB plus ISAGA was not statistically significant (P = 0.31), and we conclude that both combinations of tests can be used for the diagnosis of CT in newborns.

Sources of toxoplasma infection in pregnant women: European multicentre case-control study. European Research Network on Congenital Toxoplasmosis

OBJECTIVE

To determine the odds ratio and population attributable fraction associated with food and environmental risk factors for acute toxoplasmosis in pregnancy.

DESIGN

Case-control study.

SETTING

Six large European cities.

PARTICIPANTS

Pregnant women with acute infection (cases) detected by seroconversion or positive for anti-Toxoplasma gondii IgM were compared with pregnant women seronegative for toxoplasma (controls).

MAIN OUTCOME MEASURES

Odds ratios for acute infection adjusted for confounding variables; the population attributable fraction for risk factors.

RESULTS

Risk factors most strongly predictive of acute infection in pregnant women were eating undercooked lamb, beef, or game, contact with soil, and travel outside Europe and the United States and Canada. Contact with cats was not a risk factor. Between 30% and 63% of infections in different centres were attributed to consumption of undercooked or cured meat products and 6% to 17% to soil contact.

CONCLUSIONS

Inadequately cooked or cured meat is the main risk factor for infection with toxoplasma in all centres. Preventive strategies should aim to reduce prevalence of infection in meat, improve labelling of meat according to farming and processing methods, and improve the quality and consistency of health information given to pregnant women.

Neonatal screening for congenital toxoplasmosis in the Poznań region of Poland by analysis of Toxoplasma gondii-specific IgM antibodies eluted from filter paper blood spots

OBJECTIVES

The aims of the study were to determine the prevalence of congenital toxoplasmosis at birth in the Poznań region of Poland, the value of the serologic examination of filter paper blood specimens collected from newborns for the diagnosis of congenital Toxoplasma infection and the duration of anti-Toxoplasma-specific IgM antibodies in infants' sera.

MATERIALS AND METHODS

All neonates born in the maternity wards of the University Hospital of Gynaecology and Obstetrics in Poznań and in 10 selected obstetrics wards in the district hospitals were included. Blood samples were collected on filter paper cards, between the first and sixth day of life, screened for anti-Toxoplasma-specific IgM antibodies by an immunocapture enzyme-linked immunosorbent assay and if positive further analyzed for specific IgG and IgA antibodies.

RESULTS

Between June, 1996, and October, 1998, filter paper samples from 27,516 liveborn infants were tested, which constituted approximately 75% of all births and 83% of liveborn neonates from the Poznań region. Anti-T. gondii-specific IgM antibodies were found in 13 newborns, equivalent to a prevalence of Toxoplasma-specific IgM in newborns of 1 per 2,117 liveborn children (0.47 per 1,000) or 1 per 870 children (1.15 per 1,000) born to seronegative women at risk of primary T. gondii infection during pregnancy. We identified two congenitally infected infants who were IgM-negative at birth, had a classic triad of clinical symptoms during the first year of life and had high levels of specific IgG. The birth prevalence of congenital toxoplasmosis in the Poznań region was at least 1 per 1,834 live births (0.55 per 1,000) or 1 per 754 live neonates born to seronegative women (1.33 per 1,000). The sensitivity of the IgM assay on eluate from filter paper was not more than 86.7%, and the mean duration of IgM detectable by enzyme-linked immunosorbent assay in serum samples was the first 4.8 weeks of life.

CONCLUSION

In Poland the screening for congenital toxoplasmosis detecting one case per each 2,000 live births could be considered for inclusion in existing national neonatal screening programs for phenylketonuria and congenital hypothyroidism.

IgG recognizing 21-24 kDa and 30-33 kDa tachyzoite antigens show maximum avidity maturation during natural and accidental human toxoplasmosis

We describe the avidity maturation of IgGs in human toxoplasmosis using sequential serum samples from accidental and natural infections. In accidental cases, avidity increased continuously throughout infection while naturally infected patients showed a different profile. Twenty-five percent of sera from chronic patients having specific IgM positive results could be appropriately classified using exclusively the avidity test data. To take advantage of the potentiality of this technique, antigens recognized by IgG showing steeper avidity maturation were identified using immunoblot with KSCN elution. Two clusters of antigens, in the ranges of 21-24 kDa and 30-33 kDa, were identified as the ones that fulfill the aforementioned avidity characteristics.

Intraocular anti-Toxoplasma gondii IgA antibody production in patients with ocular toxoplasmosis

PURPOSE

To investigate the immunoglobulin classes associated with the intraocular anti-Toxoplasma gondii antibody response during clinical ocular toxoplasmosis and to determine which immunoglobulin class is most helpful in the diagnosis of this disease.

METHODS

Paired serum and intraocular fluid samples from 155 patients who had uveitis were tested for intraocular anti-T. gondii IgG, IgA, and IgM antibody production. The presence of T. gondii DNA was determined by polymerase chain reaction. Patients were divided into two groups, based on the initial clinical diagnosis; group 1 included 78 patients with presumed ocular toxoplasmosis, and group 2 included 77 patients with uveitis that was not clinically suspected to be ocular toxoplasmosis. Samples from 27 nonuveitis patients who underwent intraocular surgery were used as control subjects. The final diagnosis was based on the clinical course and interpretation of laboratory tests.

RESULTS

A final diagnosis of ocular toxoplasmosis was made in 88 of 155 patients (group 1, 68; group 2, 20). Among these patients, 65% had intraocular IgG production, 52% had intraocular IgA production, 37.5% had both IgG and IgA production, 27% had IgG production only, and 15% had IgA production only. Of the 13 patients tested, only one had intraocular IgM production. Intraocular IgA could not be detected in patients who had final diagnoses other than ocular toxoplasmosis or in control subjects. A positive polymerase chain reaction combined with a test that was positive for intraocular IgG production had a sensitivity of 77%, which increased to 91% after the detection of intraocular IgA production was added.

CONCLUSIONS

Immunoglobulin G is the major class involved in the humoral immune response against the T. gondii parasite, followed by IgA. The determination of IgA production is useful as an additional test in the diagnosis of ocular toxoplasmosis.

Lack of value of specific IgA detection in the postnatal diagnosis of congenital toxoplasmosis

To improve the performance of the postnatal diagnosis of congenital toxoplasmosis, we assessed the detection of IgA antibodies to Toxoplasma gondii by ELISA, compared with that of IgM by ELISA, ISAGA, and IFAT and neosynthesized antibodies using Western blot. From 1993 to 1996, IgA antibodies were detected using the Toxo IgA test (SFRI, Société Française de Recherches et d'Investissements, Bordeaux, France), in 195 serum and cord blood samples from 63 infants born to mothers who seroconverted during pregnancy. Eighteen infants had proven congenital toxoplasmosis (confirmed by the presence of IgG after 12 months of life) and 45 had no congenital toxoplasmosis (negativity of IgG after 6-12 months of life). The sensitivity of IgA detection by ELISA on serum and cord blood samples was 38.9 and 54.5% respectively, which is low when compared with the sensitivity of IgM detection by ISAGA (66.7% on serum samples, 90.9% on cord blood), ELISA (61.1% on sera, 81.8% on cord blood) and Western blot (83.3% on sera, 72.7% on cord blood). IgA antibodies were never detected by ELISA earlier than IgM or neosynthesized Ig (antibodies synthesized by infants). Thus, the detection of IgA antibodies by Toxo IgA is not useful in improving the diagnosis of congenital toxoplasmosis.

Detection of Toxoplasma gondii in 94 placentae from infected women by polymerase chain reaction, in vivo, and in vitro cultures

The biological diagnosis of congenital toxoplasmosis at birth is important to determine the infant's treatment. The aim of this study was to evaluate the placenta results in the congenital toxoplasmosis diagnosis and to compare them with those obtained with other samples collected at birth (cord blood and newborn blood). A total of 94 placentas, of which 33 came from fetuses suspected of or with proven congenital toxoplasmosis (CT+) and 61 from definitely or probably non-infected fetuses (CT-), was analysed by in vitro culture, mouse inoculation and polymerase chain reaction (PCR). The PCR sensitivity was higher (60.9 per cent) than that of cell culture (29.6 per cent) and mouse inoculation (51.5 per cent) but the number of PCR positive results in CT - patients was also higher (9.5 per cent). The presence of Toxoplasma gondii in the placenta tissues was the only argument at birth (IgM and neosynthesized Ig were negative) in three out of the 33 CT+ cases. The detection of IgM by ELISA and ISAGA and the detection of neosynthesized Ig by immunoblotting were more satisfactory to diagnose congenital toxoplasmosis but the placenta analysis was important to improve the sensitivity of the diagnosis at birth, especially when the prenatal diagnosis was negative or not performed.

Epidemiological study of latent and recent infection by Toxoplasma gondii in pregnant women from a regional population in the U.K

AIMS

To determine the prevalence of IgG and IgM to Toxoplasma gondii (TG) and predict the incidence of infection during pregnancy and in foetuses.

METHODS

Thirteen thousand pregnant women from eastern England were tested at the time of booking for antenatal screening. Screening was carried out for the presence of IgG and IgM anti-TG, followed by confirmation with commercially available assays.

RESULTS

Latent infection to TG was found in 7.7% of women and increased with age from 6.8 to 17.8%. Recent infection accounted for an additional 0.4% equally distributed across age groups. No difference was found between urban and rural place of residence. A 1-2% incidence of TG infection every 5 years of age was found. IgM-only cases were mostly false positives and were unsuitable for statistical analysis. On the basis of both IgM and IgG imputed data, TG infection was found significantly higher during the first trimester of pregnancy. Three to sixteen TG-infected foetuses per 10000 pregnancies were predicted.

CONCLUSIONS

The east of England has a low prevalence of TG infection and therefore a high, at-risk population of pregnant women. Repeated screening during pregnancy would be expensive, but would detect and possibly prevent infection in approximately 10 neonates per 10000 women.

The investigation of toxoplasma infection associated with pregnancy

An audit was undertaken to determine case compliance with prenatal testing and investigation of infants for toxoplasma infection. Subsequently, the effect of enhanced reference unit Intervention was studied. The proportion of cases of toxoplasma infection associated with pregnancy completing an investigation programme was calculated. The effect of continued and short-term additional intervention was assessed and reasons for failure to comply were sought. The status of the child was established in 30% of cases when acute maternal toxoplasma infection was detected. Continuous reference unit intervention significantly improved case compliance to 45% over a 3-year period, but the effect was lost when the additional measures were withdrawn. Failure to complete the investigation procedure was associated with loss of patient-clinician contact and clinician/laboratory error. Enhanced intervention did not result in a significant improvement in compliance with the investigation programme for babies with clinical abnormality. The benefits of testing for toxoplasma infection associated with pregnancy are limited by failure to complete necessary investigations.

Enzyme immunoassays for IgG and IgM antibodies to Toxoplasma gondii based on enhanced chemiluminescence

AIMS

To evaluate the clinical performance of enzyme immunoassays for IgG and IgM antibodies to Toxoplasma gondii based on enhanced chemiluminescence.

METHODS

Classification of routine clinical samples from the originating laboratories was compared with that obtained using the chemiluminescence based assays. Resolution of discordant results was achieved by testing in alternative enzyme immunoassays (IgM) or by an independent laboratory using the dye test (IgG).

RESULTS

Compared with resolved data, the IgM assay was found to be highly specific (100%) with a cut off selected to give optimal performance with respect to both the early detection of specific IgM and the detection of persistent levels of specific IgM (sensitivity 98%). Compared with resolved data, the IgG assay was shown to have a sensitivity and a specificity of 99.4%.

CONCLUSIONS

The Amerlite Toxo IgM assay possesses high levels of sensitivity and specificity. Assay interference due to rheumatoid factor like substances is not a problem. The Amerlite Toxo IgG assay possesses good sensitivity and specificity, but is less sensitive for the detection of seroconversion than methods detecting both IgG and IgM.

The diagnosis of toxoplasmosis using IgG avidity

Current methods to establish the duration of toxoplasma infection in pregnant women and for the diagnosis of toxoplasmosis in the neonate or HIV infected patient have significant limitations. We assessed the precision of a commercial ELISA for the detection of toxoplasma specific IgG and adapted the assay to measure avidity using an elution agent washing step. The sensitivity and specificity of the ELISA were 100 and 75% respectively and optimal measurement of avidity was achieved using 6 M urea as the elution agent. Toxoplasma lymphadenopathy of less than 3 months duration was associated with low avidity specific IgG but some discordant findings were recorded. Serial measurement of IgG avidity assisted the distinction between actively produced antibody in infants with congenital toxoplasmosis and passively acquired antibody of maternal origin in uninfected babies. There was no significant difference between avidity levels in HIV infected patients with or without cerebral toxoplasmosis.

Application of the polymerase chain reaction to the diagnosis of human toxoplasmosis

Toxoplasmosis may cause significant damage to the developing fetus and is a life-threatening opportunistic infection in immunocompromised persons. Serological investigation is unreliable, while isolation of the parasite is time consuming and may lack sensitivity. We have developed a system for detecting Toxoplasma gondii based on the amplification of the P30 gene using sequential rounds of PCR and nested primers. The clinical value of this technique was assessed by the investigation of a range of tissues taken from pregnant women, fetuses, neonates, AIDS patients and organ graft recipients. The PCR assay produced more positive reactions than isolation of the parasite by means of cell culture or animal inoculation. Extended autoradiography was found to be more sensitive than stained agarose gels for detecting the PCR product. Systematic contamination of PCR reactions was avoided but it was not possible to exclude sporadic contamination in certain cases. Detection of specific DNA is of clinical value in the investigation of the pregnant woman in order to assess the risk of transplacental passage of infection and in the fetus and neonate to identify congenital toxoplasmosis. Even so, PCR findings must be interpreted with caution because of the risk of a sample being contaminated. PCR may be the investigation of choice when brain biopsy is performed on a patient with AIDS and when toxoplasmosis associated with bone marrow transplantation is suspected.

Laboratory techniques in the investigation of toxoplasmosis

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Coccidian infections in AIDS. Toxoplasmosis, cryptosporidiosis, and isosporiasis

Cryptosporidium sp. and Isospora belli are coccidian protozoan parasites that were long recognized as pathogens for many animal species. The medical community became acquainted with these organisms with the advent of AIDS. Both parasites are associated with persistent, debilitating enteritis and, in the case of Cryptosporidium, biliary tract involvement in patients with AIDS. For the immunocompetent host, infection with these two pathogens usually results in self-limited diarrhea. Cryptosporidiosis appears to occur more often than isosporiasis, but the true prevalence of both infections for various populations of humans is unknown. Clinically, cryptosporidiosis is indistinguishable from isosporiasis. Diagnosis is based on finding the acid-fast (red staining oocyst in stained fecal specimens). There is no known effective therapy for cryptosporidiosis, whereas patients with isosporiasis respond promptly to treatment with trimethoprim-sulfamethoxazole. Patients with AIDS and isosporiasis have a high relapse rate after achieving complete remission and therefore need to be maintained on suppressive therapy. Much more needs to be learned about these two fascinating, "newly recognized" parasites.

Incidence of toxoplasmosis in patients with glandular fever and in healthy blood donors

The differential diagnosis of the clinical syndrome of glandular fever may include Epstein-Barr virus, cytomegalovirus and Toxoplasma gondii infection. Some general practitioners and clinical laboratories choose to perform serological investigations for toxoplasmosis in all patients with glandular fever, who have negative Paul-Bunnell test results. The validity of this approach was assessed by a comparison of the incidence of toxoplasmosis in healthy blood donors and in a group of patients with clinically diagnosed glandular fever who had negative Paul-Bunnell tests. The results showed no significant difference in the frequency of acute or chronic toxoplasma infection between the two groups. In view of these findings, together with evidence of the lack of appropriate effective therapy for toxoplasmosis in immunocompetent individuals, and the dangers of failing to recognize concurrent severe disease of a separate aetiology, we recommend that Paul-Bunnell negative patients with clinically diagnosed glandular fever are not investigated for toxoplasmosis as a routine. However, these guidelines do not apply to patients at risk of severe sequelae from toxoplasma infection, notably pregnant women, who still require a full assessment.

Postoperative necrotising granulomas in the ovary

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Serological investigation of ocular toxoplasmosis

The limitations of serological assessment in toxoplasma infection of the eye are well recognised, but the predictive value of clinical examination is not defined. We undertook a prospective investigation into the role of clinical examination and of serological findings in cases of suspected toxoplasma infection of the eye by means of the dye test and multiple IgM assays. Seventy-four cases of retinal disease and 202 control patients were studied. Patients with retinal disease had a significantly higher incidence of toxoplasma seropositivity than the control group. This was because some patients with retinal disease had acquired the infection congenitally. Half the patients investigated for toxoplasmosis were seronegative. Possible explanations for these findings included misdiagnosis, clinical uncertainty, or, the use of serology testing in the confirmation of other diseases. An excess of IgM reactivity among the retinal disease group may indicate low level immunoglobulin-M production associated with an acute exacerbation of ocular toxoplasmosis. There is a need to consider invasive procedures in cases of ocular infection and for novel techniques to aid the diagnosis of toxoplasma retinochoroiditis.

Duration of toxoplasma infection

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New methods in the diagnosis and management of cerebral toxoplasmosis associated with the acquired immune deficiency syndrome

Cerebral toxoplasmosis is a life-threatening condition associated with the acquired immune deficiency syndrome (AIDS). Current diagnostic and therapeutic methods have serious limitations. The diagnosis of cerebral toxoplasma infection in a patient with AIDS was assisted by the detection of specific IgM in a highly sensitive immunosorbent agglutination assay and by the demonstration of Toxoplasma gondii nucleic acid in a brain biopsy specimen by means of the polymerase chain reaction. Following initial failure of the patient to respond to treatment with sulphadiazine and pyrimethamine, clinical improvement was observed during treatment with clindamycin followed by dapsone. Further assessment of novel methods in the management of cerebral toxoplasmosis is required.

Selective antenatal screening for toxoplasmosis and the latex agglutination test

Recent publicity concerning congenital toxoplasmosis has generated a demand for serological assessment of pregnant women. Many laboratories are requested to undertake primary screening in these cases. We assessed the latex agglutination test (LAT) findings in 158 specimens with detectable toxoplasma specific IgM derived from pregnant women. The LAT titres ranged from 16 to greater than or equal to 4000 reflecting the variable antibody response observed in acute toxoplasmosis. We recommend that non-reference laboratories test specimens from pregnant women using the LAT at a screening dilution of 1:16 and select all reactive samples for detailed investigation.

Serological study of the prevalence of toxoplasmosis in asymptomatic patients infected with human immunodeficiency virus

Asymptomatic individuals seropositive for antibody to human immunodeficiency virus (HIV) were investigated for the presence of toxoplasma specific antibody. Serological examination was performed using multiple assays. Of 500 patients studied 133 had serological evidence of previous exposure to Toxoplasma gondii. Specific IgM was detected in 7 patients using ISAGA and 2 patients by DS-ELISA. The immunoglobulin-G annual seroconversion rate was calculated to be 0.75%. The results of this study indicate 27% of HIV positive patients in the UK are at risk of developing life-threatening secondary reactivation of cerebral toxoplasmosis in association with AIDS. A further 0.5-1% per year may suffer primary toxoplasmosis.

False-negative dye-test findings in a case of fatal toxoplasmosis associated with cardiac transplantation

False-negative dye-test results were recorded in a case of fatal toxoplasmosis associated with cardiac transplantation. Serological and histological data require individual consideration in cases of suspected toxoplasma infection of the immunocompromised.