Improved diagnosis of primary Toxoplasma gondii infection in early pregnancy by determination of antitoxoplasma immunoglobulin G avidity

Spiramycin treatment of Toxoplasma gondii infection in pregnant women impairs the production and the avidity maturation of T. gondii-specific immunoglobulin G antibodies

The aim of the study was to evaluate the influence of treatment with spiramycin on the increase of immunoglobulin G (IgG) titers and IgG avidity indexes (AI) in pregnant women with seroconversion from the beginning of therapy until delivery and after delivery. This group was compared with adult patients with recently acquired untreated toxoplasmosis. One hundred four samples from 32 pregnant women with seroconversion for toxoplasmosis and/or very low IgG AI were followed from the beginning of therapy with spiramycin until delivery. Twenty-nine women were further followed some months after delivery and interruption of therapy. Thirty-eight samples from 16 untreated, nonpregnant patients were evaluated as the control group. The Toxoplasma gondii-specific IgG antibody and the T. gondii-specific IgG AI were significantly delayed in pregnant women receiving therapy compared to nonpregnant, untreated controls, and the findings were consistent with the results of assays from two different manufacturers. The T. gondii-specific IgG AI increased in pregnant women after they gave birth. Avidity maturation is delayed during pregnancy and treatment, and low-avidity antibodies in pregnant women within 3 to 4 months cannot be taken as a sign of infection.

Value of 2 IgG avidity commercial tests used alone or in association to date toxoplasmosis contamination

Toxoplasmosis acquired during pregnancy exposes the fetus to congenital toxoplasmosis. Avidity tests are commonly used to date time of infection to evaluate the fetal risk and to offer prenatal diagnosis. This study evaluated and compared 2 commercial avidity tests: Platelia Toxo IgG Avidity (Bio-Rad, Marnes la Coquette, France) and Liaison(R) Toxo IgG Avidity II (Diasorin, Saluggia, Italy) kits. In complement, a study of specific IgG and IgM in the 2 systems was carried out. Sensitivity and specificity of the avidity tests were 94.4% and 87.8% for the Liaison(R) and 91.3% and 98.5% for the Platelia methods, respectively. Percentages of complete discrepancies, partial discrepancies, and agreement between both tests were 1.1%, 23.6%, and 75.3%, respectively. Moreover, the combination of both avidity tests may be useful in some cases. Indeed, that strategy permitted to confirm without delay a chronic toxoplasmosis in 23 cases and avoid treatment in these pregnant women.

Comparative evaluation of three commercial Toxoplasma-specific IgG antibody avidity tests and significance in different clinical settings

Determination of the avidity of specific IgG antibodies has become a generally accepted diagnostic aid for dating Toxoplasma infection. In this study, the Labsystems, VIDAS and EUROIMMUN Toxoplasma IgG avidity assays were compared on a series of 133 Toxoplasma IgG- and IgM-positive sera from symptomatic patients (n=28), from pregnant (n=43) and non-pregnant (n=26) women, and on 18 IgG-positive and IgM-negative sera from chronically infected patients. The results showed excellent concordance between the Labsystems and VIDAS tests in both the IgM-positive (r=0.82, κ=0.771) and IgM-negative (κ=0.609) sera, whilst the agreement of the EUROIMMUN assay with both the Labsystems and VIDAS tests in the IgM-positive sera was moderate (κ=0.575 and κ=0.525, respectively) and in the IgM-negative sera was poor (κ=0.000). Analysis of the kinetics of the maturation of avidity in 13 patients in whom follow-up sera were available showed that, despite a general trend of maturation, in two patients the avidity did not become high during 6 and 11 months of follow-up. In view of the clinical setting, in the symptomatic patients, despite one case of complete discrepancy and five cases of partial discrepancy, the Labsystems and VIDAS tests were in almost perfect agreement (κ=0.812), whilst the agreement in pregnant and non-pregnant women was substantial (κ=0.754 and κ=0.708, respectively). In conclusion, the Labsystems and VIDAS tests are equally reliable for the measurement of Toxoplasma IgG avidity; the choice of test should depend on the laboratory set-up. The EUROIMMUN test may be an acceptable alternative in resource-limited settings, but should be used prudently.

Quantitative real-time polymerase chain reaction for the accurate detection of Toxoplasma gondii in amniotic fluid

Infection with Toxoplasma gondii during pregnancy is often asymptomatic and may cause severe fetal damage. A quantitative TaqMan minor groove binder real-time polymerase chain reaction (PCR) assay was developed for the specific and sensitive detection of the previously described 529-bp repeat element occurring up to 200 to 300 times in T. gondii genome. The qualitative and quantitative detection limits determined were 6 and 20 marker copies (1/30 to 1/50 of 1 parasite) per PCR, respectively. In addition to standard PCR cycling conditions, 3 different fast PCR protocols were evaluated to minimize run time. A higher variability but no loss of specificity was observed. For the evaluation of clinical applicability, a total of 135 amniotic fluid samples were analyzed targeting both 529-bp and B1 gene. The sensitivity and specificity were 88.0% and 100.0% for B1, and 100.0% and 98.2% for 529-bp PCR assay (positive predictive value and negative predictive value: 100.0% and 97.4%, and 92.6% and 100.0%, respectively). Our results demonstrated an increased sensitivity of the 529-bp PCR assay even in a faster protocol.

Use of SAG2A recombinant Toxoplasma gondii surface antigen as a diagnostic marker for human acute toxoplasmosis: analysis of titers and avidity of IgG and IgG1 antibodies

We evaluated the reactivity of IgG and IgG1 antibodies by immunoassays in sera from patients with acute and chronic phases of toxoplasmosis against 2 recombinant antigens, SAG2A (full molecule) and SAG2ADelta (truncated molecule from the epitope recognized by A4D12 monoclonal antibody [mAb]), in comparison with soluble Toxoplasma antigen (STAg). Results demonstrated higher IgG reactivity in acute sera with both STAg and SAG2A than in chronic phase sera, and this difference was more evident for IgG1 antibodies to SAG2A. Low reactivity to SAG2ADelta was found in sera from both phases. ELISA-IgG-SAG2A showed high sensitivity (95%) and specificity (100%). ELISA-IgG1-SAG2A sensitivity was significantly higher (90%) for acute than for chronic (67%) phases. ELISA-IgG avidity using STAg demonstrated high performance for characterizing sera with high avidity (>60%), whereas the ELISA-IgG1 avidity-SAG2A immunoassay was the best to define chronic phase infection. It can be concluded that SAG2A is an antigen that may be used as a diagnostic tool to characterize the acute phase Toxoplasma gondii infection. Also, the epitope recognized by A4D12 mAb may be critical for the recognition of this molecule.

Determination of the relative avidity of the specific IgG antibodies in human toxocariasis

Human toxocariasis is a zoonosis caused by infection with larvae of the ascarid nematode Toxocara canis and, less frequently, T. cati. Our study developed a method for distinguishing distant from recent human toxocariasis by assessing the avidity of the IgG antibodies. The avidity of specific antibodies increases with time after antigen challenge and assessment of the degree of avidity can be used to discriminate between recent and distant infections. The relative avidity was measured in 150 sera from children with visceral toxocariasis and in 46 sera from children with ocular toxocariasis. The probable time of infection was estimated on the basis of the medical history and clinical syndrome. Our study showed that 94.2% of positive sera collected from patients reporting infection > 6 months ago had high IgG avidity values, confirming distant toxocariasis, whereas 25.9% of positive sera taken < 6 months after infection showed low indices of IgG avidity. Our results suggest that measurement of the specific IgG avidity may assist in discriminating between recent and distant toxocariasis. The method can be used effectively to rule out (because of high avidity) a recently acquired infection. Low avidity is less reliable in discriminating between recent and distant infections.

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.

Anti-HCV IgG avidity index in acute hepatitis C

BACKGROUND

The diagnosis of acute hepatitis C (AHC) is based on seroconversion to positive anti-HCV, which is usually not clinically possible.

OBJECTIVE

To determine if avidity of anti-HCV IgG can be used for the diagnosis of AHC infection.

STUDY DESIGN

We enrolled 40 consecutive patients with AHC, 16 drug addicts (IVDA) with exacerbation of chronic hepatitis C (IVDA e-CHC group), 21 non-IVDA with exacerbation of chronic hepatitis C (IVDA-free e-CHC group) and 40 with chronic hepatitis C (CHC group). HCV avidity index (HCV-AI) was determined by ELISA on sera pre-diluted 1:10 with 1M guanidine.

RESULTS

On admission, HCV-AI values were significantly lower in the AHC group (mean+/-S.D.: 0.50+/-0.30) than in IVDA-free e-CHC group (0.97+/-0.08, p<0.0001), IVDA e-CHC group (0.90+/-0.29, p<0.0001) or CHC group (1.06+/-0.20, p<0.0001). An HCV-AI lower than 0.7 obtained within the 8th day of illness distinguished patients with AHC infection from the IVDA-free e-CHC cases. An increase in HCV-AI was observed in 24 (72.7%) of 33 in AHC group, in none of 13 in IVDA-free e-CHC group and in 3 (27.3%) of 11 in IVDA e-CHC group.

CONCLUSION

HCV-AI is useful in identifying AHC infection in patients observed within the 8th day from the onset of symptoms.

Improved method to calculate the antibody avidity index

The methods currently used to determine the immunoglobulin avidity index (AI) require the choice of a reference point in the ELISA titration curve. Since both curves, with and without denaturating reagents, seldom run in parallel, the AI value becomes highly dependent on this reference. The new method for AI calculation presented here takes into account the whole data of the ELISA titration curve in which the final numerical AI is the average of each point.

Toxoplasmosis

Infections with Toxoplasma gondii occur worldwide, but are especially prevalent in Europe, South America and Africa. The primary problem for the diagnosis of T. gondii infection is long-lasting IgM-antibodies, thus the presence of T. gondii-specific IgM-antibodies do not necessarily indicate an acute infection. The use of a Toxoplasma-specific IgG-avidity ratio, differentiated Western blots and two-dimensional immunoblots usually resolves diagnostic problems. There is no consensus on the best strategy to control congenital toxoplasmosis. Recent European prospective, but descriptive, studies including a meta-analysis of existing cohorts have found a surprisingly small effect on maternal-fetal transmission and clinical signs in children treated for T. gondii infection diagnosed by pre- and neonatal screening programmes. No randomised studies exist on the treatment of T. gondii infection in pregnant women and newborn children with congenital toxoplasmosis. Atovaquone is the most promising new drug available, but is not yet approved for use in pregnant women and small children.

Impact of spiramycin treatment and gestational age on maturation of Toxoplasma gondii immunoglobulin G avidity in pregnant women

The objective of the present study was to investigate the maturation of immunoglobulin G (IgG) avidity after Toxoplasma gondii seroconversion during pregnancy and the factors that affect IgG avidity over time. The study used 309 serum samples from 117 women and a multiple linear mixed regression analysis to show the patterns of variation of IgG avidity throughout gestation. The IgG avidity ratios and the patterns of their evolution with time were quite diverse among the women and were statistically heterogeneous (P = 0.011); however, the trend was toward a statistically significant increase (P < 0.0001). On average, a 1.0167-fold increase was observed for each additional gestational week after the putative date of infection. At 12 weeks after putative infection (the expected IgG avidity maturation time), the mean avidity ratio was 16.6% (95% confidence interval, 15.4 to 17.9%). At all times, the avidity ratio remained significantly heterogeneous among the women (P < 0.05); for 95% of them, that ratio ranged from 7.8 to 35.3% at 12 weeks after putative infection. Maternal age at the putative time of infection did not influence the maturation of IgG avidity. However, on average, a 1.009-fold decrease (P = 0.03) in that avidity was observed for each additional week of gestational age before infection and a 1.03-fold increase (P = 0.0003) was observed for each additional week of delay to the onset of spiramycin treatment. The rate of increase in the avidity ratio was lower if infection occurred late in pregnancy and higher if the delay to treatment was long. This information cannot allow accurate determination of the delay since the time of infection. The present results provide support for interpretation of the assay and caution against overinterpretation.

Expression of antibodies directed to Paracoccidioides brasiliensis glycosphingolipids during the course of paracoccidioidomycosis treatment

Paracoccidioidomycosis (PCM) is a granulomatous disease caused by the dimorphic fungus Paracoccidioides brasiliensis. The immunoglobulin classes and isotypes of antibodies directed to acidic glycosphingolipids (GSLs) and glucosylceramide of P. brasiliensis were determined by enzyme-linked immunosorbent assay of sera from 31 PCM patients. The reactivities of 38 serum samples were analyzed by considering the stage of treatment: before antifungal treatment (n = 10), during 1 to 4 months of treatment (T1-4; n = 9), during 5 to 12 months of treatment (T5-12; n = 9), and posttreatment (PT; n = 10). Sera from healthy subjects (n = 12) were used as controls. Only the GSL Pb-1 antigen, which presents the carbohydrate structure Galfbeta1-6(Manalpha1-3)Manbeta1, was reactive with the PCM patient sera. The PCM patient sera did not react with Pb-2, which lacks the Galf residue and which is considered the biosynthetic precursor of Pb-1, indicating that the Galf residue is essential for antibody reactivity. The Pb-1 glycolipid from nontreated patients elicited a primary immune response with immunoglobulin M (IgM) production and subsequent switching to IgG1 production. The IgG1 titer increased after the start of antifungal treatment (T1-4 group), and general decreases in the anti-Pb-1 antibody titers were observed after 5 months of treatment (T5-12 and PT groups). The Pb-1 antigen, an acidic GSL with terminal Galf residue, has potential application as an elicitor of the host immune response in patients with PCM.

Use of IgG avidity ELISA to differentiate acute from persistent infection with Salmonella Dublin in cattle

AIMS

To investigate whether an immunoglobulin (Ig)G avidity ELISA can be used to differentiate between acute and persistent infection with Salmonella (S.) Dublin in cattle. To determine whether the IgG isotype, IgG(1) and IgG(2) responses in acute and persistent infections differ.

METHODS AND RESULTS

Animals were selected from two herds with long-term infection (years) and two herds recently infected (<3 months). Forty-seven animals were categorized into groups based on the persistence of their antibody level in milk. Based on titre from two serial dilutions the avidity index (AI) was calculated for IgG (IgG-AI), IgG(1) (IgG(1)-AI) and IgG(2) (IgG(2)-AI). The mean IgG-AI for suspected carrier animals with either persistently high (group 1) or persistently high to medium high (group 2) antibody levels was significantly (P = 0.003) higher (32.1% and 38.4%) than for acutely infected animals (21.7% and 22.3%). The probability of being a suspect carrier was associated with IgG-AI, antibody level in the sample and age. However, the effect of age could be the result of a biased sample selection. Specificities and sensitivities were calculated at a range of cut-off values for IgG-AI and IgG(1)-AI. Overall, IgG(2)-AI was high compared with IgG(1)-AI, and there was no difference in IgG(2)-AI between infection groups. There was no difference in the ratio IgG(2):IgG(1) for acute and persistent infection groups.

CONCLUSIONS

Assuming that a persistently high antibody response is indicative of persistent infection with S. Dublin in cattle, it can be concluded that the IgG-AI can aid in differentiating between acute and long-term infection on herd level. However, for the test to be useful as an alternative tool to repeated sampling over time for detection of persistently infected carriers during control strategies in cattle herds, the test needs to be optimized and studied further in a larger sample of well-characterized infections in cattle. The affinity of IgG(2) is higher than IgG(1) early in the S. Dublin infection. There appears to be no difference in the IgG(2)-AI between the acute and chronic infection stages.

SIGNIFICANCE AND IMPACT OF THE STUDY

For decades the strategies for detection of persistently infected cattle in S. Dublin infected herds have involved repeated bacteriological culture of faecal samples or repeated antibody measurements over several months. Both methods are time consuming and costly, leaving a new method for detection of carrier animals based on a single sampling highly desirable. This study illustrates a tool, IgG-AI, which may prove useful, although more validation of the method is required before it is used in practice.

Delayed maturation of immunoglobulin G avidity: implication for the diagnosis of toxoplasmosis in pregnant women

The low avidity of immunoglobulin G has been reported to be a useful marker of recent infection with Toxoplasma. Several investigators, however, have published discrepant result on the maturation of avidity over time. The aim of this study was to analyse persistent low avidity of immunoglobulin G in immunocompetent individuals and in pregnant women and how it could interfere in the flowchart of antenatal diagnosis of toxoplasmosis in the latter group. An international literature search was conducted together with a retrospective study of a hospital database. Eleven publications that met the inclusion criteria reported delayed maturation of avidity at a frequency ranging from 0 to 66.6% of the patients. Examination of those publications demonstrated an important heterogeneity in the type of assay used, the calculation of avidity, the cutoff above which avidity was considered to be elevated, and the delay since infection after which indices are expected to be high. In the hospital database, persistent low avidity was found even after a median follow-up period of 6 years. Different factors could interfere with maturation of avidity, such as variations between individuals, the assay system used, and, possibly, the treatment administered. The results of this study clearly demonstrate that, in a pregnant woman, an acute infection cannot be reliably diagnosed solely on the basis of low avidity of immunoglobulin G. Further investigations and standardization of assays are urgently needed. Estimation of the time of infection remains difficult, especially in cases in which the samples are drawn late in pregnancy; the final estimate must be based on several tests repeated at intervals of weeks.

Usefulness of Toxoplasma gondii recombinant antigens (GRA1, GRA7 and SAG1) in an immunoglobulin G avidity test for the serodiagnosis of toxoplasmosis

The precise diagnosis of an acute and recent Toxoplasma infection in pregnant women and the newborn child is important before treatment. This study describes a new Toxoplasma gondii IgG avidity test based on a combination of recombinant GRA1, GRA7 and SAG1 antigens and shows that this test is useful for diagnostic purposes and may replace the lysed, whole-cell antigens. Although more sera need to be tested, the results obtained here suggest that the IgG avidity test performed with rec-antigens correlated more with the stage of a T. gondii infection than the IgG avidity results obtained with the lysed, whole-cell antigen test, the VIDAS Toxo IgG avidity (bioMérieux).

Toxoplasma-IgM and IgG-avidity in single samples from areas with a high infection rate can determine the risk of mother-to-child transmission

Anti-Toxoplasma IgG-avidity was determined in 168 serum samples from IgG- and IgM-positive pregnant women at various times during pregnancy, in order to evaluate the predictive value for risk of mother-to-child transmission in a single sample, taking the limitations of conventional serology into account. The neonatal IgM was considered the serologic marker of transmission. Fluorometric tests for IgG, IgM (immunocapture) and IgG-avidity were performed. Fifty-one of the 128 pregnant women tested gave birth in the hospital and neonatal IgM was obtained. The results showed 32 (62.75%) pregnant women having high avidity, IgM indexes between 0.6 and 2.4, and no infected newborn. Nineteen (37.25%) had low or inconclusive avidity, IgM indexes between 0.6 and 11.9, and five infected newborns and one stillbirth. In two infected newborns and the stillbirth maternal IgM indexes were low and in one infected newborn the only maternal parameter that suggested fetal risk was IgG-avidity. In the present study, IgG-avidity performed in single samples from positive IgM pregnant women helped to determine the risk of transmission at any time during pregnancy, especially when the indexes of the two tests were analysed with respect to gestational age. This model may be less expensive in developing countries where there is a high prevalence of infection than the follow-up of susceptible mothers until childbirth with monthly serology, and it creates a new perspective for the diagnosis of congenital toxoplasmosis.

Comparison of the avidity index method and the serologic testing algorithm for recent human immunodeficiency virus (HIV) seroconversion, two methods using a single serum sample for identification of recent HIV infections

A study was designed to compare an avidity index method to the serologic testing algorithm for recent human immunodeficiency virus (HIV) seroconversion (STARHS) for the detection of recent HIV infection. One hundred sixty HIV-positive sera were tested. Both techniques performed similarly in identifying recent infections, although STARHS tended to misclassify more individuals that had long-standing infection as being recently infected.

Use of avidity enzyme-linked immunosorbent assay and avidity Western blot to discriminate between acute and chronic Neospora caninum infection in cattle

Avidity serological tests (avidity enzyme-linked immunosorbent assay [ELISA] and avidity Western blot) were developed and used to differentiate between acute (primary infection, reinfection, and recrudescence) and chronic Neospora caninum infection in cattle. In addition, the pattern of immunoglobulin G (IgG) avidity maturation against different specific antigens of N. caninum tachyzoites was studied. Sequential serum samples were collected from cattle naturally and experimentally infected with N. caninum. Four groups of experimentally infected cattle were included in the study and were representative of primary infection, reinfection, chronic infection, and noninfection. Serum samples were also collected from naturally infected cattle classified into nonaborting and aborting cows on the basis of clinical findings and serological profiles, and a third group composed of seronegative cows that seroconverted during the course of the experiment. All samples were tested by avidity ELISA and avidity Western blot. The IgG avidity ELISA allowed the discrimination between primary and chronic infection because all experimentally primary-infection cows showed low avidity indexes at week 4 postinfection (p.i.) compared with the high avidity values found at week 20 postinfection. However, this test did not allow the discrimination of reinfection or recrudescence from chronic infection. Regarding IgG avidity Western blot results, no antigenic markers correlating with acute (primary infection, recrudescence, and reinfection) or chronic infection were recognized. However, the 17-kD immunodominant antigen was mostly responsible for high avidity values obtained by avidity ELISA because it was intensively recognized by high-avidity antibodies in all chronically infected animals after urea treatment.

Diagnosis and management of toxoplasmosis

This article discusses the diagnosis and management of toxoplasmosis. Congenital toxoplasmosis continues to be a tragic outcome of a preventable and treatable infection. Education of patients, physicians and health policy makers on the primary and secondary preventive measures of the disease, and their execution, will undoubtedly result in lower incidence, morbidity, and mortality rates from congenital disease due to Toxoplasma gondii.

European multicenter study of the LIAISON automated diagnostic system for determination of Toxoplasma gondii-specific immunoglobulin G (IgG) and IgM and the IgG avidity index

The LIAISON system is a fully automated system based on chemiluminescence and antigen bound to magnetic microparticles. The system allows fast and precise measurement of Toxoplasma-specific immunoglobulin G (IgG) and IgM antibody levels and measurement of the IgG avidity index even at low levels of Toxoplasma-specific IgG antibodies in a single step without manual interference. Seven European centers participated in a multicenter evaluation of the LIAISON system. The sensitivity and specificity of the LIAISON system compared to the Sabin-Feldman dye test were 99.3 and 96.8%, respectively. In a comparison of the LIAISON Toxoplasma-specific IgM assay with an immunosorbent agglutination assay, the LIAISON assay had a sensitivity of 96.7% and a specificity of 95.4%. The LIAISON IgG assay showed agreements of 91, 100, and 100% with the AXSYM IgG (Abbott), VIDAS IgG (bioMerieux), and Platelia IgG (Bio-Rad) assays, respectively. The LIAISON IgM assay showed agreements of 95% with the AXSYM IgM and Platelia IgM assays, 96% with the ISAGA IgM assay (bioMerieux), and 97% with the VIDAS IgM assay. The coefficient of correlation between the LIAISON system and the VIDAS Toxoplasma-specific IgG avidity index was 0.81. By use of the Toxoplasma-specific IgG avidity index assay with specific IgM-positive samples, the diagnosis of infection with Toxoplasma gondii in early pregnancy has been improved significantly. The LIAISON avidity assay is a valuable assay for the exclusion of recently acquired infection with T. gondii (less than 4 months) in pregnant women, and it decreases significantly the necessity for follow-up testing.

Detection of immunoglobulin M antibodies specific for Toxoplasma gondii with increased selectivity for recently acquired infections

Toxoplasma gondii infections can cause serious complications in pregnant women, leading to miscarriage, stillbirth, and birth defects. Definitive diagnosis of T. gondii acute infection is therefore critical for the clinical management of a mother and her fetus. Positive immunoglobulin M (IgM) results are not sufficient as evidence of recent infection, as these antibodies are often present for many months. Further, IgG avidity and differential agglutination tests, two tests used by reference laboratories to distinguish between recent and past infections, are not always in agreement, and both methods yield a significant number of indeterminate results. We report the development of a new toxoplasma IgM immunoassay that is performed by using a bead-based immunoassay on an automated analyzer (BioPlex 2200). Initial validation included 204 samples from pregnant women and 198 samples from asymptomatic healthy adults. An overall specificity of 99% was observed. Further, 100% sensitivity for acute infections was observed for 10 well-characterized seroconversion panels. We then examined 50 samples from pregnant women, all of which were IgM positive by ELISA, which had been fully evaluated in a reference laboratory. Of the 50 samples, 34 (68%) tested positive in the BioPlex 2200 toxoplasma IgM assay, of which 32 of 34 (94%) exhibited an acute or equivocal pattern by differential agglutination. Of the 16 negative samples, 15 (94%) showed high-IgG-avidity antibodies. Collectively, these results suggest that this new toxoplasma assay shows a preferential response to IgM antibodies produced by recent infections, reducing the number of positive results for pregnant women that will require extensive additional clinical evaluation.

Reliability of immunoglobulin G antitoxoplasma avidity test and effects of treatment on avidity indexes of infants and pregnant women

The immunoglobulin G antitoxoplasma avidity test (Vidas; BioMérieux) is an immunoenzymatic test useful for excluding acute infection after the onset of pregnancy. The avidity index (AI) is the ratio of the signal in a test sample washed with urea, which disrupts low-avidity complexes, to that washed without urea. An AI of >0.3 is taken to mean that infection had occurred more than 4 months ago. The increase of the AI with time and the influence of the different treatments given to pregnant women and their newborns were evaluated. A total of 59 pregnant women (271 sera) and their 60 neonates (199 sera) were tested from 1998 to 2002. There were five groups of women based on the type and duration of treatment given. Thirteen pregnant women (group 1) did not receive any treatment, 15 (group 2), 11 (group 3), and 17 (group 4) women received treatment with spiramycin (9 MIU/day) for 0.5 to 2, 2.5 to 5, and 5.5 to 8 months, respectively, and the last 3 women (group 5) received tritherapy (pyrimethamine-sulfonamide and spiramycin alternatively) for 1.5 to 2.5 months. All of the maternal sera collected in the first 6 months had an AI of <0.30, with a mean of 0.07 (range, 0.01 to 0.21). The increase was slow (0.02/month), and there was no significant difference when comparisons were made between the treatment groups. Neonates with proven maternofetal transmission had an increasing AI, unlike those without transmission. However, long-term therapy with pyrimethamine-sulfonamide, as opposed to treatment with spiramycin alone, was found to slow down the progression of the AI. An AI of >0.2 is sufficient to exclude acute infection in pregnant women. In neonates, it is not of major use to diagnose congenital infection; however, it could be a good indicator of compliance and efficacy of treatment of infected infants.

Fast dipstick dye immunoassay for detection of immunoglobulin G (IgG) and IgM antibodies of human toxoplasmosis

A dipstick dye immunoassay (DDIA) was developed to detect immunoglobulin G (IgG) or IgM antibodies of toxoplasmosis infection in humans. The assays employ a blue colloidal dye particles (D-1) conjugated to sheep anti-human IgG and rabbit anti-human IgM as the visualizing agents and a soluble antigen of tachyzoites of Toxoplasma gondii strain RH (TSA) as the detective antigen. The mixture of dye-labeled anti-human antibody-special human antibody was captured by TSA onto a nitrocellulose membrane dipstick by means of immunochromatography. The assays are rapid (the whole test can be completed within 15 min), simple, and cheap, and they don't require any equipment. They are sensitive and specific for the detection of anti-Toxoplasma IgG or IgM antibodies and generally agree closely with the results from the enzyme-linked immunosorbent assay. The assays are especially suitable for field applications.

Differences in human antioxidized LDL autoantibodies in patients with stable and unstable angina

BACKGROUND

Autoantibodies to oxidized LDL (anti-oxLDL) have been found in the serum of patients with coronary artery disease (CAD). This study was designed to compare the differences in anti-oxLDL titers and isotypes in unstable and stable angina patients and to correlate these results with known markers of active inflammation in CAD.

METHODS

Thirty patients from a tertiary referral general hospital with documented CAD were studied. Anti-oxLDL IgG titers and its isotypes, high sensitivity C-reactive protein (hsCRP) and serum amyloid A (SAA) were measured.

RESULTS

The anti-oxLDL IgG titer was lower (p=0.03) in the unstable angina group compared to the stable angina patients (0.084+/-0.102 OD versus 0.195+/-0.149 OD, respectively). The predominant IgG isotype in both groups was IgG2. IgG4 was significantly higher (0.270+/-0.146 OD, p=0.04) in the unstable angina group versus patients with stable angina (0.198+/-0.019 OD). There was a significant inverse correlation between anti-oxLDL and hsCRP and SAA in this sample population (R=0.37, p<0.05 and R=0.36, p<0.05, respectively).

CONCLUSION

Patients with unstable angina have lower levels of anti-oxLDL IgG in the acute setting of CAD. Plaque instabilization does not seem to acutely modify the isotype subsets of anti-oxLDL IgG in these patients.

Delayed maturation of IgG avidity in congenital toxoplasmosis

The aim of this comparative study was to investigate the clinical usefulness of the measurement of Toxoplasma gondii IgG avidity in the postnatal diagnosis of congenital toxoplasmosis. IgG avidity values in serum samples from infants with congenital infection were compared with those in samples from uninfected infants, all born to mothers with toxoplasmosis acquired during gestation. This analysis revealed that IgG avidity values soon after birth reflected maternal values in the large majority of the samples. Low or borderline IgG avidity values were systematically found in the cohort of congenitally infected subjects. After birth, IgG avidity values slowly increased over time for up to 2 years in congenitally infected subjects. On the contrary, IgG avidity values in the uninfected infants remained stable over time. The presence of low IgG avidity in a newborn can be considered a marker of maternal seroconversion in the second or third trimester of gestation and, as a consequence, an indicator of risk for congenital toxoplasmosis. An IgG avidity assay can be easily carried out with antibodies eluted from dried blood spots (Guthrie cards), providing an opportunity to retrospectively evaluate the risk of congenital infection in special clinical circumstances, for example when suspicion of congenital infection arises during late infancy.

Incidence and prevalence of toxoplasmosis in Indian pregnant women: a prospective study

PROBLEM

Toxoplasmosis is a major cause of congenitally acquired infections causing high degree of morbidity and mortality in the newborns.

METHODS OF STUDY

IgG avidity method was used to distinguish the recent and more than 4 months old infection in a prospective cohort study for the first time in India. One hundred and eighty pregnant women presented in their first 4 months of pregnancy were included in this study. Their sera were tested for anti-Toxoplasma gondii antibodies using direct agglutination test, immunoglobulin (Ig)G and IgM-enzyme-linked immunosorbent assay, IgM-immunosorbent agglutination assay and VIDAS-IgG avidity.

RESULTS

Overall IgG seroprevalence rate of toxoplasmosis was 45%. Only seven women (3.3%) were found to have IgM antibodies and only two of these showed low IgG avidity indicating recent infection of <or=4 months duration. One woman aborted spontaneously at her fourth month of gestation. In remaining five women the recent infection could successfully be excluded by IgG avidity testing. All these women had uneventful pregnancy.

CONCLUSIONS

This study indicated that all IgM antibody positive pregnant must be tested for IgG avidity to rule out recent primary infection.

Toxoplasmosis

Toxoplasma gondii is a protozoan parasite that infects up to a third of the world's population. Infection is mainly acquired by ingestion of food or water that is contaminated with oocysts shed by cats or by eating undercooked or raw meat containing tissue cysts. Primary infection is usually subclinical but in some patients cervical lymphadenopathy or ocular disease can be present. Infection acquired during pregnancy may cause severe damage to the fetus. In immunocompromised patients, reactivation of latent disease can cause life-threatening encephalitis. Diagnosis of toxoplasmosis can be established by direct detection of the parasite or by serological techniques. The most commonly used therapeutic regimen, and probably the most effective, is the combination of pyrimethamine with sulfadiazine and folinic acid. This Seminar provides an overview and update on management of patients with acute infection, pregnant women who acquire infection during gestation, fetuses or infants who are congenitally infected, those with ocular disease, and immunocompromised individuals. Controversy about the effectiveness of primary and secondary prevention in pregnant women is discussed. Important topics of current and future research are presented.

Use of an immunoglobulin G avidity assay based on recombinant antigens for diagnosis of primary Toxoplasma gondii infection during pregnancy

The objective of this work was to develop an antibody-specific immunoglobulin G (IgG) avidity assay to discriminate between acute and latent phases of Toxoplasma gondii infection by using recombinant antigens. One hundred twenty-one serum samples from women who developed IgG antibodies against Toxoplasma during pregnancy were used. The IgG avidities of antibodies directed against epitopes carried by fragments of GRA3, GRA7, MIC3, and SAG1 antigens were measured by performing parallel enzyme immunoassays. The avidity index for Toxoplasma-specific antibodies against a homogeneous mixture of recombinant GRA3, GRA7, MIC3, and SAG1 antigens correlated closely with the IgG avidity of antibodies against lysed whole-cell T. gondii antigen. The avidity assay performed with the recombinant MIC3 antigen highlighted the presence of avidity low-antibodies IgG exclusively in sera collected within 2 months after primary infection. The presence of T. gondii-specific, low-avidity IgG antibodies against recombinant MIC3 antigen can be used to determine the point of infection with T. gondii within a 2-month time frame after infection.

Immunodiagnosis of primary Toxoplasma gondii infection in sheep by the use of a P30 IgG avidity ELISA

Toxoplasma gondii is a protozoan parasite with a worldwide distribution. In both sheep and humans, if the parasite is encountered during pregnancy, fetal infection and abortion can occur. Therefore, Toxoplasma infection in sheep has a major economic impact upon sheep farming. Clinically, there is a need to distinguish recent (acute) infections from longstanding (chronic) infections. However, current serological techniques, such as detection of anti-T. gondii IgG, cannot discriminate between acute and chronic infections. Increasing immunoglobulin avidity is a good determining factor of how recent an infection is. In this study, we describe the application and validation of a T. gondii IgG avidity ELISA, based on the use of an affinity-purified, native T. gondii P30 antigen. The assay was used to examine sera from eight sheep experimentally infected with T. gondii and found that all seroconverted within 21 days post-infection (p.i.), beginning with avidities that were initially low but that increased over time, with all sheep reaching high IgG avidity within 10 weeks p.i. In addition, sera from clinically healthy but T. gondii-seropositive lambs and ewes and seropositive ewes with a history of abortion were also subjected to a preliminary serological investigation. High IgG avidities were found in 80% of the seropositive lambs, in 90% of the clinically healthy ewes and in 97% of the ewes with abortion problems. These findings indicate that the animals had most likely contacted the parasite a longer time ago.

Negative immunodiffusion test results obtained with sera of paracoccidioidomycosis patients may be related to low-avidity immunoglobulin G2 antibodies directed against carbohydrate epitopes

Immunodiffusion (ID) is the serologic test most frequently used for the diagnosis and posttherapy follow-up of patients with paracoccidioidomycosis (PCM). The ID test is highly specific (100%), but its sensitivity is relatively low (90%), leading to false-negative results. The aim of this study was to determine the profiles of antibodies in sera from patients with proven PCM and with negative results in the ID test (IDneg) versus positive results in the ID test (IDpos). We analyzed 46 sera from patients with active PCM for total immunoglobulin G (IgG) and IgG subclass responses to Paracoccidioides brasiliensis gp43 antigen (treated or not treated with sodium metaperiodate) by enzyme-linked immunosorbent assay and immunoblotting. Immunoblotting showed that both IDneg and IDpos sera recognized predominantly the gp43 fraction of the P. brasiliensis antigen used in the ID test. IDneg sera contain low-avidity antibodies, low levels of specific IgG (total) and IgG1, and high levels of IgG2 compared with IDpos sera. The antibodies present in IDneg sera were predominantly directed against carbohydrate epitopes, since treatment with sodium metaperiodate resulted in a significant decrease in antibody reactivity. These data suggest that the lack of reactivity of sera from PCM patients in the ID test may be related to the production of low-avidity IgG2 antibodies directed against carbohydrate epitopes.

Prenatal testing for infectious disease

Prenatal testing for infectious diseases is performed frequently and for a variety of indications. The purpose of this article is to review the maternal and fetal infections that pose diagnostic concerns. Recent advances in diagnostic testing (such as avidity testing) is included. Testing issues focus on the diagnosis of maternal and fetal infection.

Identifying recent HIV infections using the avidity index and an automated enzyme immunoassay

We evaluated a procedure for identifying recent HIV infections, using sequential serum samples from 47 HIV-positive persons for whom the seroconversion date could be accurately estimated. Each serum sample was divided into two aliquots: one diluted with phosphate-buffered saline and the other diluted with 1 M guanidine. We assayed the aliquots with the automated AxSYM HIV1/2gO test (Abbott Diagnostics Division), without modifying the manufacturer's protocol. We then calculated the avidity index (AI): the ratio of the sample/cutoff value for the guanidine aliquot to that of the phosphate-buffered saline aliquot. We analyzed 216 serum samples: 34 samples were collected within 6 months of seroconversion (recent seroconversions), and 182 were collected after 6 months. The mean AIs, by time from seroconversion, were 0.68 +/- 0.16 (within 6 months) and 0.98 +/- 0.10 (after 6 months) (P < 0.0001). AI of <0.90 correctly identified 88.2% of recent infections but misclassified as recent infections 13.2% of serum samples collected afterward. The probability of an infection being classified as recent and having AI of > or = 0.90 would be 0.7% in a population with 5% recent infections. AI can identify with a certain degree of accuracy recent HIV infections, and being a quantitative index, it provides different levels of sensitivity and specificity, depending on the selected cutoff value. The standard assay procedure is not modified. This test is simple and inexpensive and could be used for surveillance, decision-making in treatment, and prevention.

Assessment of antibody avidity in aborting cattle by a somatic Neospora caninum tachyzoite antigen IgG avidity ELISA

A Neospora caninum IgG avidity ELISA was carried out on the basis of a somatic N. caninum tachyzoite antigen. The test was validated using experimentally infected calves, where a clear maturation of the IgG avidity over time could be demonstrated. At a maximum of 82 days after infection (d.p.i.), all animals showed antibody avidities ranging above 35%, and respective sera were thus defined as highly avid. Sera of 103 naturally infected seropositive cows with abortion (N. caninum association was provided by a N. caninum PCR-positivity of the fetus in 40 cases) and 139 seropositive animals without abortion history were concurrently examined. Significantly lower avidities were observed in aborting cows when compared to animals without abortion problems (P<0.01). While the avidity of sera collected before abortion remained practically constant until abortion, a significant increase of avidity could be observed in samples collected weeks to months after abortion (P<0.01). The avidities of non-aborting animals from farms with or without abortion problems did not differ significantly with time and were mainly located in the high avidity area. These data indicate that low avidities are not necessarily linked to recent N. caninum infection but can also be an indicator for increased abortion risk in cattle.

Precision and accuracy of a procedure for detecting recent human immunodeficiency virus infections by calculating the antibody avidity index by an automated immunoassay-based method

We evaluated the precision and accuracy of a procedure for detecting recent human immunodeficiency virus (HIV) infections, specifically, the avidity index (AI) calculated using a method based on an automated AxSYM HIV 1/2gO assay (Abbott). To evaluate precision, we performed multiple replicates on eight HIV-positive serum samples. To evaluate the accuracy in identifying recent infections (i.e., within 6 months of seroconversion), we used 216 serum samples from 47 persons whose dates of seroconversion were known. To evaluate the sensitivity and specificity of the procedure for different AI cutoff values, we performed receiver operating characteristic (ROC) analysis. To determine the effects of antiretroviral treatment, advanced stage of the disease (i.e., low CD4-cell count), and low HIV viral load on the AI, we analyzed 15 serum samples from 15 persons whose dates of seroconversion were unknown. The precision study showed that the procedure was robust (i.e., the total variance of the AI was lower than 10%). Regarding accuracy, the mean AI was significantly lower for samples collected within 6 months of seroconversion, compared to those collected afterwards (0.68 +/- 0.16 versus 0.99 +/- 0.10; P < 0.0001), with no overlap of the 95% confidence intervals. The ROC analysis revealed that an AI lower than 0.6 had a sensitivity of 33.3% and a specificity of 98.4%, compared to 87.9 and 86.3%, respectively, for an AI lower than 0.9. Antiretroviral treatment, low CD4-cell count, and low viral load had no apparent effect on the AI. In conclusion, this procedure is reproducible and accurate in identifying recent infections; it is automated, inexpensive, and easy to perform, and it provides a quantitative result with different levels of sensitivity and specificity depending on the selected cutoff.

Comparison of two commercially available avidity tests for toxoplasma-specific IgG antibodies

BACKGROUND

IgG anti-Toxoplasma avidity tests have proven useful to discriminate between recent and distant infection in management of pregnant women with anti-Toxoplasma-IgM antibodies. This study was performed to compare two commercially available IgG anti-Toxoplasma avidity test kits.

METHODS

Sixty-four samples positive for IgM and IgG anti-Toxoplasma antibodies were analyzed with two IgG anti-Toxoplasma avidity tests: VIDAS Toxo IgG avidity kit (BioMérieux, Marcy-l'Etoile, France) and Toxoplasma gondii IgG avidity EIA kit (Labsystems, Helsinki, Finland). Samples were obtained from both pregnant women and subjects in different clinical settings.

RESULTS

Of 64 sera positive in both VIDAS Toxo IgG and VIDAS Toxo IgM tests, 19 (29.7%) had high avidity antibodies in VIDAS and 17 (26.6%), high avidity antibodies in Labsystems kit. A total of 48 (75.0%) of 64 sera showed concordant results between VIDAS and Labsystems Toxo IgG avidity tests; one (1.2%) serum sample showed discordant results and in 15 (23.4%) sera, results were high or low in one test and borderline in the other. Overall correlation coefficient for results obtained in both tests was 0.80 (0.60 in sera of pregnant women and 0.88 in sera of other patients, respectively).

CONCLUSIONS

Correlation between results obtained in BioMérieux and Labsystems Toxo IgG avidity kits in sera from pregnant women as well other individuals was high. BioMérieux assay possesses the advantage of automatization but requires the VIDAS machine; in contrast, Labsystems assay is less costly but requires time-intensive manual performance and calculation of test results.

VIDAS test for avidity of Toxoplasma-specific immunoglobulin G for confirmatory testing of pregnant women

Because congenital toxoplasmosis is almost solely the result of maternal infection acquired during gestation, it is critical to determine whether infection during pregnancy has occurred. In the United States, definitive diagnosis of the acute infection and the time of its occurrence have been compromised by a lack of systematic screening and the fact that only a single serum sample is submitted for testing. In studies in Europe, and depending on the method used, the demonstration of high-avidity immunoglobulin G (IgG) toxoplasma antibodies has been shown to exclude infection having occurred in the first 3 to 5 months of pregnancy. We investigated the usefulness of determining the avidity of IgG toxoplasma antibodies with a VIDAS kit (herein referred to as the VIDAS Toxo-IgG avidity kit, the VIDAS kit essentially rules out acute infection having occurred within the 4 prior months) in the setting of a reference serology laboratory in the United States. Sera (132 samples) from 132 women in the first 16 weeks of pregnancy were chosen because at least one test in the toxoplasma serological profile (TSP) suggested or was equivocal for a recently acquired infection. High-avidity antibodies were demonstrated in 75% of 99 sera positive with the IgM enzyme-linked immunosorbent assay (ELISA) and 31.3% of 16 sera with acute TSP results. A significant percentage of sera with equivocal results wtih the IgM ELISA or TSP also had high-avidity test results. Of 39 women for whom treatment with spiramycin had been suggested to attempt to prevent congenital transmission, 19 (48.7%) had high-avidity antibodies. These findings highlight the value of the VIDAS IgG avidity kit when used in combination with the TSP to exclude recent infection, especially when only a single serum sample is available.

Molecular diagnosis of toxoplasmosis

Toxoplasmosis is an anthropozoonotic disease endemic world-wide, caused by the apicomplexan Toxoplasma gondii. Although the course of infection is generally benign, it can cause significant morbidity and mortality in the developing fetus and in immunocompromised individuals. Biological diagnosis classically relies upon serology and direct detection of the parasite by inoculation to laboratory animals. In the past decade, the use of the polymerase chain reaction (PCR) has made a significant improvement in both the prenatal diagnosis of congenital toxoplasmosis and the detection of acute disease in the immunocompromised patient. Nevertheless, like many 'in-house' PCR assays, the PCR-Toxoplasma suffers from lack of standardization and variable performance according to the laboratory. A wide variety of primers has been used in different assays, but few comparative tests have been performed. Moreover, in contrast to other parasitic diseases, PCR-Toxoplasma has not yet attained a sufficient level of sensitivity, regardless of the clinical condition considered. These drawbacks are discussed, together with the undoubted gain that PCR has brought to this difficult diagnosis.

Laboratory diagnosis of Toxoplasma gondii infection and toxoplasmosis

For the past 40 years, the Toxoplasma Serology Laboratory at the Palo Alto Medical Foundation Research Institute (TSL-PAMFRI) has been dedicated to the laboratory diagnosis of Toxoplasma gondii infection and toxoplasmosis. TSL-PAMFRI is the "brain child" of Jack S. Remington. Jack's ceaseless devotion to objectivity and uncompromising excellence has made TSL-PAMFRI the Toxoplasma reference laboratory for the Centers for Disease Control and Prevention, the US Food and Drug Administration, and health care providers and clinical laboratories in the United States and other countries. Jack's leadership and vision created, defined, and significantly contributed to the development of laboratory methods for the diagnosis of the infection and diseases caused by T. gondii. A summary of the laboratory tests currently available at TSL-PAMFRI for the diagnosis of infection and disease caused by the parasite is presented here.

Major carbohydrate antigen of Echinococcus multilocularis induces an immunoglobulin G response independent of alphabeta+ CD4+ T cells

Echinococcus multilocularis causes alveolar echinococcosis, one of the most lethal helminthic (accidental) infections in humans, as the life cycle predominantly includes wildlife rodents as intermediate hosts. The physical barrier between the proliferating parasitic metacestode and the host tissue is the acellular laminated layer (LL), which is characterized by its rich high-molecular-weight polysaccharide composition. Conversely to a crude protein-rich vesicular fluid antigen, a major carbohydrate antigen of the LL--the Em2(G11) antigen--did not stimulate murine T-cell proliferation in vitro. In fact, the persistent metacestode growth and antigenic stimulation induced a Th2 shift in vivo following conventional infection by intraperitoneal inoculation of 100 metacestode vesicles into C57/BL6 mice. Concurrently, the expression of Th1 cytokines (interleukin-2 and gamma interferon) remained persistently low until the late stage of chronic infection. In comparison to a recombinant proteinic II/3 antigen, the specific immunoglobulin G (IgG) response against the Em2(G11) antigen (including all IgG isotypes) maintained persistently low avidity. Furthermore, the Em2(G11) antigen induced a specific IgM and IgG response in T-cell-deficient athymic nude, TCRbeta(-/-), major histocompatibility complex class II (MHCII)(-/-)(CD4-deficient), and CD40(-/-) mice. The Em2(G11)-specific IgG synthesized in nude TCRbeta(-/-) and MHCII(-/-) mice was predominantly of the IgG3 and IgG2a isotypes and of the IgG3 and IgG2b isotypes in CD40(-/-) mice. This finding suggested that in vivo, the IgG response to major carbohydrate antigen Em2(G11) of E. multilocularis could take place independently of alphabeta+ CD4+ T cells and in the absence of CD40-CD40 ligand interactions; thus, the Em2(G11) antigen of the acellular LL represents a T-cell-independent antigen. Functionally, the encapsulating LL, and especially its major carbohydrate antigen, Em2(G11), seems to be one of the key factors in the parasite's survival strategy and acts by modulating the host immune response by virtue of its T-cell-independent nature.

Simplified assay for measuring Toxoplasma gondii immunoglobulin G avidity

A Toxoplasma gondii immunoglobulin G (IgG) avidity enzyme-linked immunosorbent assay (ELISA) was developed that combines the accuracy of assays based on end point titers and the relative ease of assays based on optical density values. Like published procedures, the new assay's avidity index (AI) was based on differential T. gondii-specific IgG reactivity in serum-treated wells washed with urea buffer versus that in wells washed with control buffer; unlike previous assays, however, the IgG reactivity was measured quantitatively using a standard curve. The assay was evaluated using 24 IgG-positive and IgM-positive sera collected within 5 months of the onset of symptoms (recent-infection group) and 25 IgG-positive and IgM-negative sera (past-infection group). All sera in the recent-infection group exhibited AI values of <0.18, whereas all sera in the past-infection group exhibited AI values of >0.27. The AI values of the recent-infection group showed significant correlation with the number of days after the onset of symptoms. A subset of 16 sera (8 recent and 8 past) was tested using a commercially available T. gondii IgG avidity ELISA based on end point titration; the results of the two assays showed highly significant correlation (R(2) = 0.9125). In addition, we confirmed and extended the findings of other investigators, showing that AI values calculated using optical density values, but not AI values calculated using quantitative IgG values, varied significantly depending on the serum dilution used. This new assay should facilitate the accurate measurement of T. gondii IgG avidity in a reference laboratory setting.

Comparison of immulite with vidas for detection of infection in a low-prevalence population of pregnant women in The Netherlands

A comparative evaluation of the Vidas system (bioMérieux, Marcy l'Etoile, France) and the Immulite System (Diagnostic Products Corporation) was performed using 500 prospectively collected serum samples. As part of a routine antenatal screening program, these samples were tested for hepatitis B surface antigen, and immunoglobulin G (IgG) and IgM antibodies to Toxoplasma gondii and rubella virus. The overall agreement between the two assay systems ranged from 98.0 to 99.8%. After discrepancy analysis the outcome in terms of relative sensitivity and specificity varied from 97.5 to 100%.

Congenital toxoplasmosis: a review

Toxoplasmosis is caused by infection with the protozoan parasite Toxoplasma gondii. In the United States, approximately 85% of women of childbearing age are susceptible to acute infection with T. gondii. Acute infections in pregnant women may cause serious health problems when the organism is transmitted to the fetus (congenital toxoplasmosis), including mental retardation, seizures, blindness, and death. An estimated 400 to 4000 cases of congenital toxoplasmosis occur in the U.S. each year. Manifestations of congenital toxoplasmosis may not become apparent until the second or third decade of life. Serologic tests are used to diagnose acute infection in pregnant women, but false-positive tests occur frequently, therefore, serologic diagnosis must be confirmed at a reference laboratory before treatment with potentially toxic drugs should be considered. Much of congenital toxoplasmosis can be prevented by educating women of childbearing age and pregnant women to avoid eating raw or undercooked meat, to avoid cross-contamination of other foods with raw or undercooked meat, and to use proper cat-litter and soil-related hygiene.

The prevalence and avidity of Toxoplasma gondii IgG antibodies in pigs from Brazil and Peru

Raw or inadequately cooked pork is an important source of Toxoplasma gondii infection, and the infection rate in animals used as human food, is an important risk predictor. The prevalence of this infection was estimated in 396 sera from 5-month old pigs obtained at abattoirs in São Paulo, Brazil (300) and Lima, Peru (96). The seroprevalence was higher in pigs from Peru (32.3%) as compared to Brazil (9.6%), as detected by ELISA and Western blot. Hemagglutination gave poor resolution which was not useful for the diagnosis of T. gondii infection. Specific antibody avidity is correlated with infection time, as shown in experimentally infected piglets. Using an arbitrary cut-off of 50% avidity index, Brazilian pigs were found to be more recently infected than Peruvian pigs. Pork should be considered a significant source of human T. gondii infection both in Brazil and Peru. Avidity assays could help in the detection of the time of T. gondii infection in pigs, allowing preventive management.

Lack of utility of specific immunoglobulin G antibody avidity for serodiagnosis of reactivated toxoplasmosis in immunocompromised patients

The avidities of Toxoplasma-specific immunoglobulin G serum antibodies were measured in immunocompromised patients presenting with cerebral or extracerebral toxoplasmosis and/or serological reactivation. Since avidity remained high and stable in 39 of 40 patients with toxoplasmosis and 27 of 28 patients with serological reactivation, we conclude that this test cannot help diagnose toxoplasmosis in these patients.

Avidity of islet cell autoantibodies in non-diabetic children and children with insulin-dependent diabetes

Low-avidity immunoglobulin G antibodies, which commonly occur after microbial infections and form unstable complexes with the antigen, are within weeks replaced by high-avidity antibodies, which bind the antigen tightly and characterise mature immune response. We hypothesised that avidity of islet cell autoantibodies (ICA), found in the sera of patients with insulin-dependent diabetes mellitus (IDDM) usually months or years before disease onset, might reflect the stage of progression towards overt IDDM. ICA were quantitated before and after treatment of antigen-antibody complexes with 5 M urea in a new assay, in which the fluorescence intensity of europium chelate-labelled detecting antibody is measured from a digital time-resolved fluorescence image. The proportion of urea-resistant ICA of all ICA was defined as the avidity index. The median avidity indices (range) of 119 children with recent-onset IDDM and 64 non-diabetic ICA-positive children were 74% (23-100%) and 11% (0-100%), respectively (p = 0.0001). The avidity indices of only 3 children with IDDM (2.5%), but of 55 non-diabetic ICA-positive children (86%) were < 40%. In conclusion, our data show that ICA avidity indices of ICA-positive non-diabetic children and children with IDDM differ, suggesting that measurement of ICA avidity may improve prediction of the time of onset of clinical IDDM.

Recombinant antigens to detect Toxoplasma gondii-specific immunoglobulin G and immunoglobulin M in human sera by enzyme immunoassay

We have evaluated the diagnostic utility of eleven Toxoplasma gondii recombinant antigens (P22 [SAG2], P24 [GRA1], P25, P28 [GRA2], P29 [GRA7], P30 [SAG1], P35, P41 [GRA4], P54 [ROP2], P66 [ROP1], and P68) in immunoglobulin G (IgG) and IgM recombinant enzyme-linked immunosorbent assays (Rec-ELISAs). Following an initial evaluation, six recombinant antigens (P29, P30, P35, P54, P66, and P68) were tested in the IgG and IgM Rec-ELISAs with four groups of samples which span the toxoplasmosis disease spectrum (negative, chronic infection, acute infection, and recent seroconversion). Our results suggest that the combination of P29, P30, and P35 in an IgG Rec-ELISA and the combination of P29, P35, and P66 in an IgM Rec-ELISA can replace the tachyzoite antigen in IgG and IgM serologic tests, respectively. The relative sensitivity, specificity, and agreement for the IgG P29-P30-P35 Rec-ELISA were 98.4, 95.7, and 97.2%, respectively. The resolved sensitivity, specificity, and agreement for the IgM P29-P35-P66 Rec-ELISA were 93.1, 95.0, and 94. 5%, respectively. Relative to the tachyzoite-based immunocapture IgM assay, the IgM P29-P35-P66 Rec-ELISA detects fewer samples that contain IgG antibodies with elevated avidity from individuals with an acute toxoplasmosis.

Serological diagnosis of Neospora caninum infection

Since the first isolation of the apicomplexan parasite Neospora caninum, a range of serological assays have been developed for use in dogs, cattle and a variety of other potential host species. The tests include the indirect fluorescent antibody test, the direct agglutination test and different enzyme-linked immunosorbent assays. This article reviews the principles and properties of the available tests which are discussed in relation to different applications.

A new method with general diagnostic utility for the calculation of immunoglobulin G avidity

The reference method for immunoglobulin G (IgG) avidity determination includes reagent-consuming serum titration. Aiming at better IgG avidity diagnostics, we applied a logistic model for the reproduction of antibody titration curves. This method was tested with well-characterized serum panels for cytomegalovirus, Epstein-Barr virus, rubella virus, parvovirus B19, and Toxoplasma gondii. This approach for IgG avidity calculation is generally applicable and attains the diagnostic performance of the reference method while being less laborious and twice as cost-effective.

Early recognized antigen (p34) of Toxoplasma gondii after peroral ingestion of tissue cyst forming strain (Me49 strain) in mice

Serum from mouse orally ingested with tissue cyst forming strain (Me49) of Toxoplasma gondii was assayed by Western blot and immunofluorescene assay (IFA) to establish early responses in antigenicity of the parasite in mouse model of foodborne toxoplasmosis. Sera were collected weekly to blot the RH antigen transferred onto nitrocellulose paper after being separated by 12% SDS-PAGE. With the second week serum, 34 kDa protein (p34) was detected uniquely, and all antigens of T. gondii were detected with the sera from 3 or 4 weeks. p34 was not a member of the major surface membrane proteins and confirmed to be localized in the rhoptry by IFA. It was secreted into parasitophorous vacuolar membrane (PVM) during the entry into host cells. When applied to the human sera of which the ELISA absorbance was in negative range, 10.3% of sera detected p34, while all the ELISA positive sera detected the band. It has diagnostic usefulness of presumed T. gondii infection. We suggest the name of the p34 protein as ROP9.