Evaluation of a Commercial IgG/IgM Western Blot Assay for Early Postnatal Diagnosis of Congenital Toxoplasmosis

The aim of this study was to evaluate a commercial Western blot IgG/IgM assay for use in the early serological diagnosis of congenital toxoplasmosis. This assay compares the immunological profile of mother and infant and allows differentiation between passive transmitted maternal antibodies and newly synthesized antibodies of the infant within the first 3 months of life. Over a 6-year period (1995–2001), the sera from 169 mothers and their 175 offspring (6 had twins) were examined for specific anti-Toxoplasma gondii IgG, IgM and IgA antibodies with an enzyme-linked immunosorbent assay or an immunosorbent agglutination assay. All mothers had primary Toxoplasma infection during pregnancy. Serological and clinical follow-up of the infants during the first year of life confirmed 36 cases of congenital toxoplasmosis. In 139 cases, infection could be ruled out. Three hundred fifty-one paired samples from 175 mother-child pairs were tested retrospectively for IgG and IgM patterns by Toxoplasma Western blot IgG/IgM (LDBIO Diagnostics, France). The results of conventional serological analysis (immunosorbent agglutination assay or enzyme-linked immunosorbent assay) to detect IgM or IgA were compared with the results of the Toxoplasma Western blot IgG/IgM on samples obtained within the first 3 months of life. The performance of the combination of the two methods was also assessed. At birth, the sensitivity values of conventional serological analysis and the Toxoplasma Western blot were 52% and 67%, with specificity values being 99% and 96%, respectively. Combination of the Western blot and conventional serological analysis increased the sensitivity at birth to 78% and within the first 3 months of life to 85%. Overall, the combination of both methods detected 94% of congenital infections. Therefore, this commercial Western blot represents a useful tool for early postnatal diagnosis of congenital toxoplasmosis. Electronic Publication     

Diagnostic significance of immunoglobulin M antibodies to Toxoplasma gondii detected after separation of immunoglobulin M from immunoglobulin G antibodies.

Failure to demonstrate immunoglobulin M (IgM) antibodies by indirect immunofluorescence (IgM-IFA) in sera from some patients with acute acquired toxoplasmosis has recently been attributed to an inhibitory effect of high titers of IgG antibodies in these sera (Pyndiah et al. J. Clin. Microbiol. 9:170-174, 1979). To confirm these findings and define their importance for diagnosis, we used gel filtration to separate IgM from IgG antibodies in a series of sera that were negative in the IgM-IFA test. A total of 68 sera were from patients with acquired toxoplasmosis, 13 were from uninfected adults, 13 were from infants with congenital toxoplasmosis, and 7 were from uninfected neonates. Of the 68 sera from patients with acquired toxoplasmosis, IgM preparations (from the separated sera) were positive in the IgM-IFA test in 36 (53%). There was a significant (P = 0.00003) association between high titers of IgM-IFA antibodies in the IgM preparations (corrected for dilution of IgM antibodies by the gel filtration procedure) and recent acquisition of infection. IgM antibodies were also detected in 5 (38%) of the IgM preparations of 13 sera from congenitally infected infants but not in any of the IgM preparations of sera from uninfected neonates. IgG antibodies to Toxoplasma gondii were shown to interfere with demonstration of IgM antibodies in the IgM-IFA test. Treatment of sera with protein A resulted in greater dilution of IgM antibodies and less efficient separation of IgM from IgG antibodies than did separation of sera by gel filtration. Treatment of sera with protein A did not result in increased detection of IgM antibodies to T. gondii. Testing of IgM preparations (obtained by gel filtration) resulted in a significant increase in sensitivity of the IgM-IFA test for the diagnosis of recently acquired and congenital toxoplasmosis.     

Performance of a Western Blot Assay to Compare Mother and Newborn Anti-Toxoplasma Antibodies for the Early Neonatal Diagnosis of Congenital Toxoplasmosis

 The aim of this study was to retrospectively evaluate the performance of a Western blot assay to compare mother and newborn anti-Toxoplasma gondii antibodies for the early neonatal diagnosis of congenital toxoplasmosis. Since specific anti-Toxoplasma IgM or IgA is detected inconstantly at birth in the neonate, the diagnosis of congenital toxoplasmosis is often delayed until 6–9 months, after IgG titers have been observed persistently. In this study, 81 paired samples from 60 mother/child pairs were tested for IgG and IgM patterns. All mothers had (or were strongly suspected to have) acquired toxoplasmosis during pregnancy. Specific IgM and IgA were simultaneously detected by immunocapture tests, and IgG was titrated. A serological and clinical follow-up of infants was conducted during the first year of life until the diagnosis of congenital toxoplasmosis could be either confirmed or ruled out. Seventeen of the 60 newborns were congenitally infected. Specific IgM or IgA was detected by immunocapture at birth in 76.5% and 70.6% of cord sera from infected neonates, respectively, with an equal specificity of 77.5%. Comparative Western blot allowed the detection of neosynthesized IgG and IgM in the cord blood of 50% and 78.6% of infected infants, respectively, with a specificity of 100%. The combination of IgA and IgM immunocapture tests, the analysis of IgG and IgM Western blot patterns, and the combination of both techniques allowed the detection of 94%, 94%, and 100% of cases within the first 3 months of life, respectively. In conclusion, Western blotting seems to be a useful complementary tool for the early postnatal diagnosis of congenital toxoplasmosis.     

IgA antibody response during acquired and congenital toxoplasmosis.

Toxoplasma gondii specific IgA and IgM antibodies were quantitated by an antibody capture agglutination assay in 260 patients with acquired toxoplasmosis and from 94 fetuses suspected of congenital toxoplasmosis and 30 infected children. In acquired toxoplasmosis, IgA antibodies to T gondii were found in 95% of the cases. In congenital toxoplasmosis IgA antibodies were more frequently detected (75%) in cord blood than IgM antibodies (61%). They persisted after birth, in some cases for up to 24 months. IgA antibodies were also detected in fetuses whose mothers had toxoplasmosis during their pregnancy. In infected fetuses IgM and IgA antibodies were detected in fetal blood as early as week 24 of pregnancy. Detection of IgA T gondii antibodies may be useful for the diagnosis of some recently acquired infection and for the diagnosis and follow up of the infection in the fetus and neonate.     

Antibody response of HIV-infected patients to latent,cerebral and recently acquired toxoplasmosis

The aim of this longitudinal study with 626 HIV-infected patients was to evaluate the capability of serological tests in diagnosing the presence of Toxoplasma gondii infection in HIV-infected patients, as well as the potential impact of various treatment regimes on serological results. Low IgG antibody levels and stable or declining titres predominated. IgM positivity occurred in ten patients (one seroconversion, seven latent, two cerebral toxoplasmosis). Complement fixation test (CFT) titres ≥1:32 imply that the relative risk of cerebral toxoplasmosis is 6.84 (95% confidence interval [CI] 1.44–32.5) but with a predictive value of only 14.0% (95% CI 5.3–27.9). Values of specific antibodies are not biassed by antiretroviral treatment and/or prophylaxis for toxoplasmosis, and the detection of specific antibodies is very useful in the identification of T. gondii infection in the HIV-infected population, but the role of serology in predicting the clinical manifestation of T. gondii infection is limited.     

Evaluation of the Liaison Automated Testing System for Diagnosis of Congenital Toxoplasmosis

Congenital toxoplasmosis is a worldwide health problem, and different screening strategies exist. Testing of toxoplasma-specific antibodies in infants identifies congenital toxoplasmosis during the first year of life. However, experience with commercial available immunoassays is limited. The aim of this study was to evaluate both the performance and analytical characteristics of the Liaison diagnostic system in infants. In a retrospective study, serum Toxoplasma gondii antibodies were measured in samples from 333 infants, including 212 noninfected infants and 121 infants with congenital toxoplasmosis. A total of 1,157 umbilical cord blood and peripheral serum samples were analyzed. Liaison toxoplasma-specific IgG and IgM antibodies and the IgG avidity index were compared to the infection status of the infant, determined by the Sabin-Feldman dye test and immunosorbent agglutination assay—IgM. All noninfected infants were seronegative by Liaison IgG within the first year of life. The Liaison system showed a sensitivity of 81.8%, a specificity of 100.0%, a positive predictive value of 100.0%, a negative predictive value of 90.6%, and overall agreement of 84.4% by comparison with the dye test. Overall agreement of both IgM test systems was 96.0%. In this study cohort, avidity did not show a potential diagnostic benefit for the detection of congenital infection. In conclusion, the Liaison system is a valuable tool to monitor the serologic course of infants at risk. A final serologic confirmatory test is recommended to improve the rate of detection of congenital toxoplasmosis at 1 year of life. Protocols of routine follow-up testing in infants and accurate diagnostic tools after acute gestational infections are needed to improve medical care.     

Immunoglobulin M-immunosorbent agglutination assay for diagnosis of infectious diseases: diagnosis of acute congenital and acquired Toxoplasma infections.

An immunoglobulin M (IgM)-immunosorbent agglutination assay (IgM-IS-AGA) was negative in all sera from individuals negative in the Sabin-Feldman dye test, in sera from individuals with chronic Toxoplasma infection, and in cord blood samples from uninfected infants. In contrast, all sera that were obtained from individuals with a recent history of acute Toxoplasma infection and from infants with congenital Toxoplasma infection and that were positive in both the dye test and the IgM-indirect fluorescent-antibody (IgM-IFA) test were positive in IgM-ISAGA. A total of 21 (67.7%) of 31 sera that were negative in the IgM-IFA test, despite being obtained from individuals with recently acquired Toxoplasma infection, and 8 (72.7%) of 11 sera that were negative in the IgM-IFA test and obtained from infants with congenital Toxoplasma infection were positive in IgM-ISAGA. The presence of rheumatoid factor, antinuclear antibodies, or both did not cause false-positive results in the IgM-ISAGA but did so in the IgM-IFA test. Thus, IgM-ISAGA in both more sensitive and more specific than the IgM-IFA test for detection of IgM antibodies to Toxoplasma gondii and, therefore, for the diagnosis of acute congenital and acquired Toxoplasma infections.     

An enzyme-linked immuno-filtration assay used to compare infant and maternal antibody profiles in toxoplasmosis

Enzyme-linked immuno-filtration assay is carried out on a micropore membrane. This doubly analytical technique permits simultaneous study of antibody specificity by immunoprecipitation and characterisation of antibody isotypes by immuno-filtration with enzyme-labelled antibodies. Recognition of the same T. gondii antigenic constituent by IgG, IgA, IgM or IgE antibodies produces couplets (IgG-IgM; IgG-IgA) or triplets (IgG-IgM-IgA; IgG-IgM-IgE) which identify the functional fractions of the toxoplasmosis antigen. In acquired toxoplasmosis, the persistence of IgM antibody long after infestation puts in question the implication of recent infestation normally linked to detection of this isotype. For sera of comparable titres, comparison of immunological profiles by the method described demonstrates disparities in the composition of the specific antibody content as expressed in international units. Use of the same method to detect IgM antibodies or distinguish between transmitted maternal IgG and IgG antibodies synthesised by the foetus or neonate makes a diagnosis of congenital toxoplasmosis possible in 85% of cases during the first few days of life. With the method described the diagnosis may be made on average 5 months earlier than with classical techniques. In the course of surveillance for latent congenital toxoplasmosis, the appearance of IgM or IgE antibodies raises the possibility of complications (hydrocephalus, chorioretinitis). After cessation of treatment, a rise in IgG antibodies indicating persistence of infection is detected earlier by the present than by classical methods.     

Cellular Immunity to <Emphasis Type="Italic">Toxoplasma gondii</Emphasis> in Congenitally Infected Newborns and Immunocompetent Infected Hosts

The aim of this study was to determine the frequency of anergy to Toxoplasma gondii in congenitally infected newborns and immunocompetent infected individuals. Specific anergy to Toxoplasma has been reported previously, especially in cases of congenital toxoplasmosis. Whole blood from 592 immunocompetent patients with suspected toxoplasmosis was cultured in the presence of soluble Toxoplasma antigen for 7 days. Activated T lymphocytes were detected by flow cytometry. In patients over 1 year of age, the percentage of soluble Toxoplasma antigen-stimulated T cells expressing the interleukin-2 receptor CD25 was higher in infected patients than in uninfected subjects (40.0±18.3% vs. 1.8±2.0%, P<0.0001). No differences were detected between seroconverters, i.e. those with recent rises in IgM and IgG antibodies, and those with acquired or congenital toxoplasmosis. Similar results were observed when congenitally infected (n=38) and uninfected (n=89) children under 1 year of age were compared (17.6±9.2% vs. 3.0±4.9%, P<0.0001). The sensitivity and specificity values of CD25 detection for diagnosis of congenital toxoplasmosis in infants were 95% and 89%, respectively, at a threshold value of 7% above control culture. The results show that specific cellular immunity is detectable in virtually all Toxoplasma-infected patients, including newborns. Detection of CD25 constitutes a simple, sensitive and specific test for diagnosis of congenital toxoplasmosis. Electronic Publication     

Early neonatal diagnosis of congenital toxoplasmosis: value of comparative enzyme-linked immunofiltration assay immunological profiles and anti-Toxoplasma gondii immunoglobulin M (IgM) or IgA immunocapture and implications for postnatal therapeutic strategies.

Diagnostic strategies for congenital toxoplasmosis have changed profoundly in recent years. Immunological diagnostic methods, long considered disappointing, can now be used at a very early stage. Over a 3-year period, 1,050 infants at risk of congenital toxoplasmosis (born to 1,048 mothers infected during pregnancy) were monitored for a minimum of 12 months and a maximum of 7 years. More than 6,000 serum specimens were analyzed by comparative mother-infant immunological profiles (CIPs) based on an enzyme-linked immunofiltration assay (ELIFA) and an immunocapture method for the detection of specific immunoglobulin M (IgM) and IgA. IgG antibodies were also titrated. One hundred three cases of congenital toxoplasmosis were demonstrated. The CIP-ELIFA method had a better diagnostic yield (sensitivity, 90%) than specific IgM and/or IgA detection by immunocapture assay (sensitivity, 77%). By using a combination of these tests, congenital infection was diagnosed in the first month and the first 3 months of life in 90 and 94% of infants with toxoplasmosis, respectively, with a specificity of 99.8% and a positive predictive value of 99% at 8 months of age. This dual diagnostic approach (ELIFA and IgM-IgA immunocapture) is highly efficient and has important implications for therapy. Indeed, early postnatal diagnosis based on objective evidence enables therapy with pyrimethamine-sulfadoxine to be started immediately for 24 months, while spiramycin (which used to be given preventively for 9 to 12 months to all infants at risk) can be stopped after the first 3 months of life.     

Detection of specific immunoglobulin E in patients with toxoplasmosis.

An immunocapture assay was developed to detect Toxoplasma gondii-specific immunoglobulin E (IgE) in sera from adults with acute acquired infection or reactivation and from babies with congenital toxoplasmosis. The components of this assay were monoclonal antibody to human IgE, samples from patients, and T. gondii tachyzoites treated with Formalin. When T. gondii-specific IgE antibodies were present, visually detectable agglutination occurred. Sera, umbilical cord blood, fetal blood, cerebrospinal fluid, and amniotic fluid were tested by this method. Specific IgE antibodies were detected in sera from 25 (86%) of 29 adults who developed specific IgG antibody during pregnancy or had specific IgA and IgM antibodies. Specific IgE was present early during infection, at the time that IgM antibodies were present, and slightly preceding the presence of specific IgA antibodies. In 23 patients tested serially, IgE antibodies never persisted for longer than 4 months. No nonspecific anti-T. gondii IgE was detected in sera from uninfected individuals. Maternal IgE antibodies did not cross the placenta. In sera of patients with congenital toxoplasmosis, specific IgE antibodies were found at birth, during the first year of life, and during immunologic recrudescence following discontinuation of pyrimethamine-sulfonamide therapy. The IgE immunocapture assay is simple to perform. It is especially useful for determining when T. gondii was acquired by recently infected pregnant women.     

Detection of Specific Immunoglobulin E during Maternal, Fetal, and Congenital Toxoplasmosis

Toxoplasma immunoglobulin E (IgE) antibodies in 664 serum samples were evaluated by using an immunocapture method with a suspension of tachyzoites prepared in the laboratory in order to evaluate its usefulness in the diagnosis of acute Toxoplasma gondii infection during pregnancy, congenital infection, and progressive toxoplasmosis. IgE antibodies were never detected in sera from seronegative women, from patients with chronic toxoplasma infection, or from infants without congenital toxoplasmosis. In contrast, they were detected in 86.6% of patients with toxoplasmic seroconversion, and compared with IgA and IgM, the short kinetics of IgE was useful to date the infection precisely. For the diagnosis of congenital toxoplasmosis, specific IgE detected was less frequently than IgM or IgA (25 versus 67.3%), but its detection during follow-up of children may be interesting, reflecting an immunological rebound. Finally, IgE was detected early and persisted longer in progressive toxoplasmosis with cervical adenopathies, so it was also a good marker of the evolution of toxoplasma infection.     

Comparative immunoglobulin G antibody profiles between mother and child (CGMC test) for early diagnosis of congenital toxoplasmosis

Early diagnosis of congenital toxoplasmosis is rendered difficult when specific immunoglobulin M (IgM) and/or IgA antibodies are absent in the blood of the newborn infant. Since maternal IgG antibodies can cross the placenta, determination of IgG antibodies in newborn infants has hitherto not been used routinely for the diagnosis of congenital infection. The aim of this study was to assess the diagnostic usefulness of an immunoblot assay which compares the early IgG profiles between the mother and her child (comparative IgG profile between mother and child; CGMC test) directed against a total cell lysate of Toxoplasma gondii tachyzoites. Serum samples from 97 newborn infants at risk of toxoplasma infection were obtained from umbilical cord blood at birth or postnatally until 3 months of life and were directly compared with serum samples from the respective mothers. Congenital toxoplasmosis was diagnosed only when IgG-reactive protein bands that were present in any newborn serum samples were absent in the corresponding maternal serum sample. Congenital infection was defined by conventional serological assays when IgM and/or IgA antibodies were present in newborn infant blood or when IgG titers rose within the first 12 months or were persistently stable for more than 8 months. Using these criteria, congenital infection was definitely confirmed in 11 cases. Three additional cases were diagnosed based on indicative data. The CGMC test, which was performed without knowledge of the results of conventional serologal assays, had sensitivity and specificity of 82.4 and 93.0%, respectively, and positive and negative predictive values of 73.7 and 95.7%, respectively. When true positives and true negatives were considered, the comparative IgG profile had a ratio of 90.9% true results. The CGMC test thus is useful as an additional assay for the rapid diagnosis of congenital toxoplasmosis when paired serum samples from mother and child are available.     

Use of recombinant antigens for early postnatal diagnosis of congenital toxoplasmosis

The main objective of this work was to improve the early serologic diagnosis of toxoplasmosis in children at risk of congenital infection by using recombinant antigens. Serum samples from 104 infants born to mothers with primary Toxoplasma gondii infection acquired during pregnancy, of which 35 were congenitally infected and 22 had clinical silent toxoplasmosis at birth, were included. Immunoglobulin M (IgM), IgG, and IgG subtype antibodies against epitopes carried by fragments of T. gondii MIC2, MIC3, MIC4, M2AP, AMA1, and SAG1 gene products were measured by performing parallel enzyme immunoassays (Rec-ELISAs). Recombinant antigens preferentially reacted with IgG antibodies from infected infants compared to uninfected subjects (P < 0.0001), indicating that sera from infected children recognized a more diverse repertoire of antigens than sera transferred over the placenta from the mothers. Using two serial samples collected within 3 months of life, it was possible to demonstrate a neosynthesis of specific anti-MIC2 and anti-SAG1 immunoglobulin G, mainly of the IgG2 subtype, in 13 out of 20 infants with congenital toxoplasmosis. IgM antibodies in 97% of infected infants reacted with at least one of the recombinant antigens, confirming the diagnosis of congenital infection as soon as 2 months after birth (P < 0.0001). The use of recombinant antigens is effective in distinguishing T. gondii-infected from uninfected infants and shows that assays based on recombinant antigens improve the diagnosis of newborns with congenital toxoplasmosis.     

Demonstration of immunoglobulin M class antibodies to Toxoplasma gondii antigenic component p35000 by enzyme-linked antigen immunosorbent assay

On the basis that 89% of 48 acute-phase toxoplasmosis patients showed immunoglobulin M (IgM) class antibodies to the 35,000-molecular-weight antigenic component (p35000) of Toxoplasma gondii, as demonstrated by IgM immunoblotting, the antigen was purified by sucrose gradient centrifugation and enzyme labeled for use in an enzyme-linked antigen immunosorbent assay (ELA) for the demonstration of IgM class antibodies to the p35000 component. The ELA showed a specificity of 96% with 139 serum specimens at a serum dilution of only 1:5. The test serologically detected 73 symptomatic acute-phase toxoplasmosis patients; 64 were positive in the 19S IgM indirect immunofluorescent-antibody test, and 9 were negative, although they showed IgM antibodies to p35000, as demonstrated by IgM immunoblotting. Also, the ELA turned out to be independent of IgM rheumatoid factors in six acute-phase toxoplasmosis serum specimens.     

Diagnosis of congenital toxoplasmosis by two-dimensional immunoblot differentiation of mother and child immunoglobulin g profiles

Differentiation between the specific immunoglobulin G (IgG) response to Toxoplasma gondii by a mother and her newborn child is helpful in the diagnosis of congenital infection with T. gondii in newborns without T. gondii-specific IgM and/or IgA antibodies at birth. Previous methods include immunoblotting and complexing T. gondii antigen with the sera from the mother and child and comparing the bands after electrophoresis. We developed a two-dimensional immunoblotting (2DIB) method with T. gondii RH strain tachyzoite antigen and validated the method with sera from 11 children identified through the neonatal screening program for congenital toxoplasmosis in Denmark. The children were identified by using Toxoplasma-specific IgM antibodies at the screening test, but the presence of T. gondii-specific IgM and/or IgA antibodies could not be confirmed at the subsequent serum sample tested. The children were monitored for at least 12 months, and in seven of eight patients monitored for 12 months the results of the 2DIB-predicted congenital infection were confirmed by the presence of persistent Toxoplasma-specific IgG antibodies. 2DIB is a sensitive technique that allows early differentiation between passively transferred maternal T. gondii-specific IgG antibodies and antibodies synthesized by the newborn child.     

Prevalence of latent toxoplasmosis and serological diagnosis of active infection in HIV-positive patients

The seroprevalence of latentToxoplasma gondii infection was determined in a cohort of 715 HIV-positive patients followed up at an HIV outpatient clinic. Using indirect immunofluorescence and direct agglutination assays for detecting IgG, the prevalence of anti-Toxoplasma gondii antibodies was shown to be 50 %. During a four-year period, clinically apparent acute toxoplasmosis occurred in 47 patients (43 with cerebral, 3 with ocular and 1 with bone marrow toxoplasmosis) among the 360 patients positive for anti-Toxoplasma gondii IgG and in one patient (with cerebral toxoplasmosis) among the 355 patients who were serologically negative. A significant rise in IgG levels could be shown during acute toxoplasmosis episodes in only 30 % of patients, compared with 3 % of patients without active toxoplasmosis. During acute toxoplasmosis, IgM antibodies were detected in only two patients (6 %) by an immunosorbent agglutination assay and in one (3 %) by an enzymatic immunocapture assay. Specific IgA was detected by a non-enzymatic immunocapture assay in six patients (18 %) during acute episodes. The very high predictive value (99.7 %) of a negative IgG test remains the best serological parameter for excluding an acute episode of toxoplasmosis in HIV-positive patients.     

Seroprevalence for toxoplasmosis in individuals living in North West Tuscany: access to Toxo-test in central Italy

This survey aimed to estimate the prevalence of anti-Toxoplasma IgG and IgM antibodies in people living in north west Tuscany (central Italy) and to investigate the adherence to antenatal screening programs and access to the Toxo-test as well. Sera from a large sample of individuals suspected to have acute infection or from pregnant women (10,352 subjects) aged between 1 day and over 70 years were analysed for both IgG and IgM anti-Toxoplasma antibodies using an immunoenzymatic method or a chemo-luminescent immunoassay. Overall, the seroprevalence of IgG antibodies was 21.4% (95% CI 20.62–22.20). A positive trend according to age was found, with low positivity observed in younger age groups. Among women of reproductive age the prevalence of IgG antibodies was 19.4% (95% CI 18.64–20.26). The overall IgM seroprevalence was 1.07% (95% CI 0.87–1.27). A low IgM prevalence was also observed in women of reproductive age (0.8%; 95% CI 0.65–1.03). Our study seems to indicate that primary prevention is widespread among women. However, an epidemiological surveillance system for toxoplasmosis should be implemented, to assess the risk of congenital toxoplasmosis and to determine the true burden of disease in adults.     

Clinical value of specific immunoglobulin E detection by enzyme-linked immunosorbent assay in cases of acquired and congenital toxoplasmosis

The clinical value of immunoenzymatic (enzyme-linked immunosorbent assay) detection of anti-Toxoplasma immunoglobulin E (IgE) was assessed by studying 2,036 sera from 792 subjects, comprising seronegative controls and subjects with acute, active, reactivated, or congenital toxoplasmosis. Included were nonimmunized adults; pregnant women with recently acquired infection (acute toxoplasmosis); immunocompetent subjects with recently acquired severe infection (active toxoplasmosis) expressed as fever, adenopathies, splenomegaly, pneumonia, meningitis, or disseminated infection; subjects-some of them immunocompromised-whose previously moderate IgG antibody levels rose, suggesting a reactivation of quiescent toxoplasmosis; and infants born to seroconverted mothers and evaluated for diagnosis of congenital infection and therapeutic management. Specific IgE antibodies were never detected in seronegative subjects. They were present in 85.7% of asymptomatic seroconverters and in 100% of seroconverters with overt toxoplasmosis, following two different kinetics: in the former, the specific IgE titer generally presented a brief peak 2 to 3 months postinfection and then fell rapidly, whereas specific IgE persisted at a very high titer for several months in the latter. IgE emerged concomitantly with the increase in IgG during toxoplasmic reactivation. For neonatal diagnosis of congenital toxoplasmosis, IgE was less informative than IgM and IgA (sensitivities, 59.5, 64.3, and 76.2%, respectively) and had a specificity of 91.9%. Nevertheless, simultaneous measurement of the three isotypes at birth improved the diagnostic yield to 81% relative to the combination of IgA and IgM. Emergence of specific IgE during postnatal treatment for congenital toxoplasmosis is a sign of poor adherence or inadequate dosing.     

Value of specific immunoglobulin a detection by two immunocapture assays in the diagnosis of toxoplasmosis

The diagnosis ofToxoplasma gondii infection is currently based on immunological tests, but tests for IgG and IgM antibodies alone are often insufficient to assess the risk of active disease, especially during pregnancy and in immunodeficient subjects. The supplementary diagnostic value of testing for antitoxoplasmic IgA in cases of acute, chronic, congenital and reactivated toxoplasmosis, relative to classical immunological tests, was evaluated using two immunocapture tests, one based on tachyzoite agglutination and the other on an immunoenzymatic complex recognizing the membrane protein P30 ofToxoplasma gondii. A total of 4,541 sera from 395 uninfected subjects, 468 immunized subjects with chronic infection, 117 subjects with acute infection and 403 children, 103 of whom had congenital toxoplasmosis, was tested. Specific IgA tests were negative in the nonimmune population, but tests for this immunoglobulin subtype became positive very rapidly during primary infection, and IgA disappeared more rapidly than IgM. In the children infected in utero, specific IgA was detected more frequently than IgM. In contrast, in a population of HIV-seropositive subjects with clinical toxoplasmosis, tests for IgA were poorly sensitive. The two tests for specific IgA produced similar results, except in the early stages of primary infection, in which immunoenzymatic testing for anti-P30 IgA was less sensitive than the agglutination method.