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

Detection of persistent low IgG avidity-an interpretative problem in the diagnosis of acute toxoplasmosis

OBJECTIVES

For the proper diagnosis of toxoplasmosis it is essential to determine the stage of the infection, for which the most preferred method is IgG avidity test. The avidity index (AI) should initially be low (AI≤0.3) in the acute phase and increase during the infection. However, persistent low avidity can occur in patients with latent toxoplasmosis, which can complicate the interpretation of the results. The aim of the study is to explain the causes of this phenomenon.

METHODOLOGY

A retrospective study was carried out with 717 serum samples collected from 442 patients from the categories of pregnant and non-pregnant women, men, and newborns + infants (age < 0.5 year). The trends of AI kinetics were evaluated in repeatedly examined patients. The frequency of cases with low avidity was compared in individual categories of patients and in groups of people with acute and non-acute toxoplasmosis.

RESULTS

The proportion of patients with initially low avidity was 42.1% in the acute toxoplasmosis group while it was 13.0% in the non-acute groups. In uninfected newborns with anti-Toxoplasma antibodies transmitted from the mother, a decrease in IgG avidity levels over time was observed, resulting in 29.2% of samples showing low (improper) avidity. While the dynamics of IgG avidity and the frequency of cases of improperly low avidity were similar in men and pregnant and non-pregnant women, the category of newborns and infants differed substantially for these indicators.

CONCLUSIONS

Due to acceptable specificity and negative predictive value, high avidity can rule out acute toxoplasmosis, but moderate sensitivity complicates the possibility of its confirmation. The results of the avidity test must be interpreted in the context of the results of other methods.

Assessment of the clinical benefits of prenatal screening for toxoplasmosis in southern Taiwan

OBJECTIVE

The present study aimed to investigate the seroprevalence and risk factors for toxoplasmosis among pregnant women in southern Taiwan and to determine the clinical benefits of screening for the same.

MATERIALS AND METHODS

The current study included 458 pregnant women who received prenatal care from the first trimester at the Kaohsiung and Chiayi Chang Gung Memorial Hospitals during the time period from 2014 to 2015. Serological tests performed to detect the presence of Toxoplasma IgG and IgM antibodies. Amniocentesis was scheduled and real-time polymerase chain reaction (PCR) was employed to detect Toxoplasma DNA. Moreover, the maternal characteristics and risk factors, perinatal outcomes related to the seropositivity for Toxoplasma infection were analyzed.

RESULTS

Among the pregnant patients included in the current study, 39/458 (8.5%) were IgG+ and 2/458 (0.6%) were IgM+. The present study analyzed the maternal characteristics and risk factors, perinatal outcome pertaining to the IgG seropositive group by means of the multiple logistic regression analysis revealed a female predominance (10.8%), compared to the males (6.4%), (adjusted OR = 0.48 (95%, 0.24-0.98), P = 0.043∗). The number cases with gestational age above 37 weeks at the time of delivery was significantly lower, compared to the cases below 37 weeks (adjusted OR = 0.32 (0.12-0.94), P = 0.038∗). Among one case with low avidity cannot exclude recent infection, the amniocentesis did not show any evidence of vertical transmission.

CONCLUSION

The scenario may not warrant general screening and the results will not influence the clinical decisions. Although the present study failed to identify the maternal risk factors related to Toxoplasma infection, the results imply that health education is essential, owing to the slightly higher rate of preterm delivery in the IgG seropositive group.

Toxoplasmosis in pregnancy

Toxoplasmosis is one of the common chronic infections caused by the parasite Toxoplasma gondii. Even though its infection in healthy non-pregnant women is self-limited and largely asymptomatic, the main concern is the risk to the fetus by vertical transmission in pregnancy. Congenital toxoplasmosis can result in permanent neurological damage and even serious morbidity such as blindness. Screening programs are implemented in various countries depending on the prevalence and virulence of the parasite in the respective regions. Upon diagnosis of infection, appropriate antibiotic therapy should be initiated as it has been proven to reduce the risk of fetal transmission. Primary prevention remains the key intervention to avoid the infection and hence patient education is an important aspect of the management.

Toxoplasma gondii-specific IgG avidity testing in pregnant women

BACKGROUND

The parasite Toxoplasma gondii can cause congenital toxoplasmosis following primary infection in a pregnant woman. It is therefore important to distinguish between recent and past infection when both T. gondii-specific IgM and IgG are detected in a single serum in pregnant women. Toxoplasma gondii-specific IgG avidity testing is an essential tool to help to date the infection. However, interpretation of its results can be complex.

OBJECTIVES

To review the benefits and limitations of T. gondii-specific avidity testing in pregnant women, to help practitioners to interpret the results and adapt the patient management.

SOURCES

PubMed search with the keywords avidity, toxoplasmosis and Toxoplasma gondii for articles published from 1989 to 2019.

CONTENT

Toxoplasma gondii-specific IgG avidity testing remains a key tool for dating a T. gondii infection in immunocompetent pregnant women. Several commercial assays are available and display comparable performances. A high avidity result obtained on a first-trimester serum sample is indicative of a past infection, which occurred before pregnancy. To date, a low avidity result must still be considered as non-informative to date the infection, although some authors suggest that very low avidity results are highly suggestive of recent infections depending on the assay. Interpretation of low or grey zone avidity results on a first-trimester serum sample, as well as any avidity result on a second-trimester or third-trimester serum sample, is more complex and requires recourse to expert toxoplasmosis laboratories.

IMPLICATIONS

Although used for about 30 years, T. gondii-specific avidity testing has scarcely evolved. The same difficulties in interpretation have persisted over the years. Some authors have proposed additional thresholds to exclude an infection of <9 months, or in contrast to confirm a recent infection. Such thresholds would be of great interest to adapt management of pregnant women and avoid unnecessary treatment; however, they need confirmation and further studies.

Microsphere-Based IgM and IgG Avidity Assays for Human Parvovirus B19, Human Cytomegalovirus, and Toxoplasma gondii

Human parvovirus B19, human cytomegalovirus, and Toxoplasma gondii are ubiquitous pathogens. Their infections are often asymptomatic or mild in the general population yet may be transmitted from mother to fetus during pregnancy. Maternal infections by these pathogens can cause severe complications to the fetus or congenital abnormalities. As a rule, the risk of maternal transmission is critically related to the infection time; hence, it is important to determine when a pregnant woman has acquired the infection. In this study, we developed new diagnostic approaches for the timing of infections by three pathogens. All the new assays appeared to be highly sensitive and specific, providing powerful tools for medical diagnosis.

Human parvovirus B19 (here B19), human cytomegalovirus (HCMV), and Toxoplasma gondii infections during pregnancy can lead to severe complications. While traditional diagnosis of infections is mostly confined to one pathogen at a time, a multiplex array is a feasible alternative to improve diagnostic management and cost-efficiency. In the present study, for these three pathogens, we developed microsphere-based suspension immunoassays (SIAs) in multiplex and monoplex formats for the detection of antimicrobial IgM antibodies as well as corresponding chaotrope-based IgG avidity SIAs. We determined the diagnostic performances of the SIAs versus in-house and commercial reference assays using a panel of 318 serum samples from well-characterized clinical cohorts. All the newly developed assays exhibited excellent performance compared to the corresponding high-quality reference methods. The positive and negative percent agreements of the IgM SIAs in comparison with reference methods were 95 to 100% and 98 to 100%, and those of the IgG avidity SIAs were 92 to 100% and 95 to 100%, respectively. Kappa efficiency values between the SIAs and the corresponding reference assays were 0.91 to 1. Furthermore, with another panel comprising 391 clinical samples from individuals with primary infection by B19, HCMV, or T. gondii, the IgM SIAs were highly sensitive for the detection of acute infections, and the IgG avidity SIAs were highly specific for the separation of primary infections from past immunity. Altogether, the strategy of IgM multiplex screening followed by IgG avidity reflex testing can provide high-throughput and accurate means for the detection and stage determination of B19, HCMV, and T. gondii infections.

IMPORTANCE Human parvovirus B19, human cytomegalovirus, and Toxoplasma gondii are ubiquitous pathogens. Their infections are often asymptomatic or mild in the general population yet may be transmitted from mother to fetus during pregnancy. Maternal infections by these pathogens can cause severe complications to the fetus or congenital abnormalities. As a rule, the risk of maternal transmission is critically related to the infection time; hence, it is important to determine when a pregnant woman has acquired the infection. In this study, we developed new diagnostic approaches for the timing of infections by three pathogens. All the new assays appeared to be highly sensitive and specific, providing powerful tools for medical diagnosis.

Congenital Toxoplasmosis: A Plea for a Neglected Disease

Maternal infection by Toxoplasma gondii during pregnancy may have serious consequences for the fetus, ranging from miscarriage, central nervous system involvement, retinochoroiditis, or subclinical infection at birth with a risk of late onset of ocular diseases. As infection in pregnant women is usually symptomless, the diagnosis relies only on serological tests. Some countries like France and Austria have organized a regular serological testing of pregnant women, some others have no prenatal program of surveillance. Reasons for these discrepant attitudes are many and debatable. Among them are the efficacy of antenatal treatment and cost-effectiveness of such a program. A significant body of data demonstrated that rapid onset of treatment after maternal infection reduces the risk and severity of fetal infection. Recent cost-effectiveness studies support regular screening. This lack of consensus put both pregnant women and care providers in a difficult situation. Another reason why congenital toxoplasmosis is disregarded in some countries is the lack of precise information about its impact on the population. Precise estimations on the burden of the disease can be achieved by systematic screening that will avoid bias or underreporting of cases and provide a clear view of its outcome.

Immunoglobulin M indirect-fluorescent antibody test for the diagnosis of acute toxoplasmosis during pregnancy in the avidity era: A 14-year experience at the Tuscany Reference Center for Infectious Diseases in Pregnancy, Florence, Italy

AIM

The aim of this study was to evaluate immunoglobulin M indirect-fluorescent antibody test (IgM IFAT) for the diagnosis of acute or chronic Toxoplasma infection in pregnancy.

METHODS

Pregnant women with suspected acute toxoplasmosis referred to the Tuscany Reference Center for Infectious Diseases in Pregnancy during the period 1998-2012 were retrospectively enrolled. All women were tested with a panel of serological tests, including enzyme-linked immunosorbent assay for IgG avidity and IgM IFAT. On the basis of anamnestic, clinical, and serological criteria, pregnant women were classified into three groups: recently infected (RI), latently infected (LI), and doubtful latently infected (DLI). Patients classified as DLI were excluded from the analysis. The association between IgM IFAT (positive or negative) and the diagnosis of infection (acute or chronic) was assessed. Positive predictive value and negative predictive value of the IgM IFAT were calculated.

RESULTS

A total of 810 pregnant women were enrolled in the study: 302 in the RI group and 508 in the LI group. Fifty-two women classified as DLI were excluded. IgM IFAT was positive in 172 out of 302 (56.9%) pregnant women in the RI group and in 29 out of 508 (5.7%) in the LI group. The positive predictive value and negative predictive value of IgM IFAT in predicting RI was 85.6% and 78.6%, respectively.

CONCLUSION

IgM IFAT has reasonable sensitivity and specificity in diagnosing recent infection and, mostly in case of borderline avidity test, could be considered as a further aid for an accurate diagnosis of acute toxoplasmosis in pregnancy.

Comparison of Toxoplasma gondii IgG avidity Architect and Vidas assays with the estimated date of infection in pregnant women

A maternal Toxoplasma gondii infection during pregnancy is a risk for congenital infection through maternal-fetal transplacental transmission. Estimation of the date of infection is of the utmost importance for management and treatment recommendations. In this setting, IgG avidity has been shown to be useful as high avidity rules out an infection dating less than 4 months. The estimated date of infection can also be obtained by the ratio of T. gondii IgG titers measured by the Vidas (bioMérieux) assay versus T. gondii IgG titers measured by the Architect (Abbott Laboratories) test, together with T. gondii IgM and IgA antibody responses. In this study, using 117 serum samples from pregnant women, we compared the IgG avidity values obtained by Architect and Vidas with the presumed date of T. gondii infection established by the T. gondii IgG ratio of IgG Vidas and IgG Architect plus the IgM and IgA results. To date, IgG avidity Vidas seems to exhibit better performance than Architect. For both assays, gray zone results were most likely obtained from patients infected more than 4 months before sampling. These data should be taken into account for a possible reconsideration of the interpretation of avidity results in the gray zone.

Toxoplasmosis, Parvovirus, and Cytomegalovirus in Pregnancy

There are several infections in adults that warrant special consideration in pregnant women given the potential fetal consequences. Among these are toxoplasmosis, parvovirus B19, and cytomegalovirus. These infections have an important impact on the developing fetus, depending on the timing of infection. This article reviews the modes of transmission as well as maternal and neonatal effects of each of these infections. In addition, the article outlines recommended testing, fetal surveillance, and treatment where indicated.

Persistent Low Toxoplasma IgG Avidity Is Common in Pregnancy: Experience from Antenatal Testing in Norway

The parasite Toxoplasma gondii might harm the fetus if a woman is infected during pregnancy. IgG seroconversion and significant increase in IgG antibody amount in pregnancy indicates maternal infection. Presence of toxoplasma immunoglobulin M (IgM), immunoglobulin G (IgG) and low IgG avidity in a single serum sample indicates possible maternal infection, but positive toxoplasma IgM and low IgG avidity may persist for months and even years. We aimed to evaluate avidity development during pregnancy in a retrospective study. Serial blood samples from 176 pregnant women admitted to Oslo University Hospital 1993–2013 for amniocentesis because of suspected toxoplasma infection were included. Data were obtained from journals and laboratory records. The avidity method used was based on Platelia Toxo IgG assay. Mean maternal age at first serology was 29.9 years (SD 5.2, range 18–42). In 37 (21%) women only the avidity increased from low to high in < 3 months. In 139 (79%) the IgG avidity remained below the high threshold ≥ 3 months and within this group 74 (42%) women had stable low IgG avidity during the observation period. Median gestational age at first test was 10.6 weeks (range 4.6–28.7). Fetal infection was detected in four children, but none among children whose mother had stable low IgG avidity. The first antenatal toxoplasma serology should ideally be collected in early pregnancy and if stable values of toxoplasma IgM and low IgG-avidity are detected in a second sample after three to four weeks, the need for amniocentesis can be questioned.

Diagnosis of toxoplasmosis and typing of Toxoplasma gondii

Toxoplasmosis, caused by the obligate intracellular protozoan Toxoplasma gondii, is an important zoonosis with medical and veterinary importance worldwide. The disease is mainly contracted by ingesting undercooked or raw meat containing viable tissue cysts, or by ingesting food or water contaminated with oocysts. The diagnosis and genetic characterization of T. gondii infection is crucial for the surveillance, prevention and control of toxoplasmosis. Traditional approaches for the diagnosis of toxoplasmosis include etiological, immunological and imaging techniques. Diagnosis of toxoplasmosis has been improved by the emergence of molecular technologies to amplify parasite nucleic acids. Among these, polymerase chain reaction (PCR)-based molecular techniques have been useful for the genetic characterization of T. gondii. Serotyping methods based on polymorphic polypeptides have the potential to become the choice for typing T. gondii in humans and animals. In this review, we summarize conventional non-DNA-based diagnostic methods, and the DNA-based molecular techniques for the diagnosis and genetic characterization of T. gondii. These techniques have provided foundations for further development of more effective and accurate detection of T. gondii infection. These advances will contribute to an improved understanding of the epidemiology, prevention and control of toxoplasmosis.

Identification of Toxoplasma gondii antigens associated with different types of infection by serum antibody profiling

Acquisition of acute toxoplasmosis during the first trimester of pregnancy can have catastrophic consequences for the foetus. Diagnosis is routinely based on the detection of maternal Toxoplasma gondii--antibodies using whole parasite extracts as detection antigen. While such assays are sensitive, they show no specificity for the stage of infection. We hypothesized diagnosis might be improved using recombinant antigens for detection, particularly if antibodies to certain antigen(s) were associated with early or late stages of infection. To address this, protein microarrays comprising 1513 T. gondii exon products were probed with well-characterized sera from seronegative ('N') controls, and acute ('A'), chronic/IgM-persisting ('C/M') and chronic ('C') toxoplasmosis cases from Turkey. Three reactive exon products recognized preferentially in A infections, and three recognized preferentially in C/M infections, were expressed in Escherichia coli and tested for discrimination in IgG ELISAs. The best discriminators were exon 1 of TGME49_086450 (GRA5) which detected C/M infections with 70.6% sensitivity and 81.8% specificity, and exon 6 of TGME49_095700 (ubiquitin transferase domain-containing protein) which detected A infections with 84.8% sensitivity and 82.4% specificity. Overall, the data support a recombinant protein approach for the development of improved serodiagnostic tests for toxoplasmosis.

Adenovirus-specific IgG maturation as a surrogate marker in acute exacerbations of COPD

BACKGROUND

B cells in airways and lung parenchyma may be involved in COPD evolution; however, whether their pathogenic role is beneficial or harmful remains controversial. The objective of this study was to investigate the maturation of adenovirus-specific immunoglobulins in patients with COPD with respect to clinical outcome.

METHODS

The presence of adenovirus-specific immunoglobulins during acute exacerbation of COPD (AECOPD) was analyzed at exacerbation and 2 to 3 weeks later. Patients with detectable adenovirus-specific IgM and low IgG avidity were grouped into fast and delayed IgG maturation. The clinical outcome of both groups was evaluated.

RESULTS

Of 208 patients, 43 (20.7%) had serologic evidence of recent adenovirus infection and were grouped by fast IgG maturation (26 patients) and delayed IgG maturation (17 patients). Baseline characteristics, AECOPD therapy, and duration of hospitalization were similar in both groups, but the AECOPD recurrence rate within 6 months was higher (P = .003), and there was a trend for earlier AECOPD-related rehospitalizations (P = .061) in the delayed IgG maturation group. The time to rehospitalization or death within 2 years was shorter in patients with delayed IgG maturation (P = .003). Adenovirus-specific IgG maturation was an independent predictor of the number of AECOPD recurrences within 6 months (P = .001) and the occurrence of hospitalization or death within 2 years (P = .005).

CONCLUSIONS

Delayed immunoglobulin avidity maturation following COPD exacerbation is associated with worse outcomes.

TRIAL REGISTRY

ISRCTN Register; No.: ISRCTN77261143; URL: www.isrctn.org.

Clinical evaluation of the Roche Elecsys CMV IgG Avidity assay

Congenital cytomegalovirus (CMV) infection has potentially severe consequences in newborns. The testing of pregnant women for CMV-specific antibodies may be useful for the identification of women at risk of transmitting the infection to the fetus. The determination of CMV IgG avidity helps to establish the timing of infection as IgG avidity matures during the course of infection. This study examines the performance of the Elecsys CMV IgG Avidity assay using preselected samples from patients at different phases of CMV infection. The Elecsys CMV IgG Avidity assay was tested at three sites using sequential samples from patients with recent primary CMV infection, as well as single samples from patients with recent primary or past CMV infection. The Elecsys assay discriminated well between early (low avidity) and late (high avidity) phases of infection in sequential serum samples. Overall, 98.8% of low-avidity samples corresponded to infection onset <180 days before sampling and 77.8% of all high-avidity results corresponded to infection onset >90 days before sampling. The assay's sensitivity was 90-97%, with specificity ranging from 89 to 100%, depending on the consideration of gray-zone avidity values. Single samples from recent primary or past infection showed similar distributions of avidity results. The Elecsys CMV IgG Avidity assay results are in agreement with preselected samples from patients with primary or past CMV infection, showing that the test is an adequate predictor of the phase of infection.

Toxoplasma seroconversion with negative or transient immunoglobulin M in pregnant women: myth or reality? A French multicenter retrospective study

Classically, Toxoplasma infection is associated with high levels of specific IgM antibody and a rise in specific IgG levels 1 to 3 weeks later. Atypical IgG seroconversion, without IgM detection or with transient IgM levels, has been described during serologic follow-up of seronegative pregnant women and raises difficulties in interpreting the results. To evaluate the frequency and the characteristics of these atypical cases of seroconversion, an investigation was conducted within the French National Reference Center for Toxoplasmosis, from which 26 cases collected from 12 laboratories belonging to the network were identified. The aim of this work was to retrospectively analyze the results of serologic testing, the treatments administered, and the results of prenatal and postnatal follow-up for these women. In each case, IgG antibodies were detected using both screening and confirmatory tests. IgM antibodies were not detected in 15 cases, and the levels were equivocal or low-positive in 11 cases. The IgG avidity results were low in 16 cases and high in one case. Most of the pregnant women (22/26) were treated with spiramycin from the time that IgG antibodies appeared until delivery. Amniotic fluid was analyzed for Toxoplasma gondii DNA by PCR in 11/26 cases, and the results were negative in all cases. Congenital toxoplasmosis was ruled out in 12/26 newborns. There was no abnormality observed at birth for 10 newborns and no information available for 4 newborns. In conclusion, when the interpretation of serological results is so difficult, it seems cautious to initiate treatment by spiramycin and to follow the pregnant women and their newborns.

Severe polymyositis due to Toxoplasma gondii in an adult immunocompetent patient: a case report and review of the literature

Toxoplasmosis, a worldwide zoonosis caused by a coccidian parasite Toxoplasma gondii, is more often asymptomatic in immunocompetent patients. We report the case of a 38-year-old immunocompetent male with a polymyositis as the presenting manifestation of T. gondii infection. The patient was hospitalized for a 30-day history of fever (T max 39.5°C), muscle pain, and progressive weakness of the muscles. A diagnosis of polymyositis was made, and he was started on corticosteroid treatment, which caused no reduction of symptoms. After finding a positive polymerase chain reaction (PCR) assay for T. gondii, together with additional clinical findings, a diagnosis of acute toxoplasmosis was made. Specific treatment with pyrimethamine and sulfadiazine was started, with a progressive reduction of symptoms and normalization of laboratory tests.

Use of dense granule antigen GRA6 in an immunoglobulin G avidity test to exclude acute Toxoplasma gondii infection during pregnancy

The usefulness of a specific immunoglobulin G (IgG) avidity enzyme-linked immunosorbent assay (ELISA) based on recombinant GRA6 antigen for distinguishing between acute and chronic Toxoplasma infection was investigated. Two sets of serum samples obtained from pregnant women with acute, chronic, or no Toxoplasma infection collected in France and Iran were used. Among the French subjects, 19 of 20 (95%) women who experienced seroconversion during the past 4 months before sampling displayed low-avidity IgG antibodies against GRA6, while all 17 (100%) women with chronic infection had high-avidity antibodies. When the Euroimmun IgG avidity ELISA was used, 15 of 19 (78.9%) recently infected women had low-avidity antibodies, and 20 of 22 (90.9%) women with chronic infection displayed high-avidity antibodies. The results suggested better performance of the GRA6 avidity ELISA than the Euroimmun avidity ELISA for exclusion of a recent infection occurring less than 4 months previously. Similarly, all 35 Iranian women with acute Toxoplasma infection had low-avidity antibodies against GRA6, whereas all 34 women with chronic infection displayed IgG antibodies of high avidity, indicating the value of GRA6 avidity testing for ruling out a recent infection. Avidity tests based on lysed whole-cell Toxoplasma gondii antigen are currently used to exclude recently acquired infections; however, the use of recombinant antigen(s) might improve the diagnostic performance of avidity tests and facilitate the development of more standardized assays.

Serology using rROP2 antigen in the diagnostic of toxoplasmosis in pregnant women

Toxoplasma gondii causes severe fetal disease during acute infection in pregnant women, thus demanding early diagnosis for effective treatment and fetus preservation. Fetal tests are inefficient and risky, and diagnosis is based on maternal IgM serology, which had weak screening ability due to increased sensitivity, with alternative IgG avidity tests. Here, we performed ELISA and avidity assays using a recombinant T. gondii antigen, rROP2, in samples from 160 pregnant women screened from a large public hospital who were referred due to positive IgM assays. IgG serology and avidity assays were compared using whole T. gondii extract or rROP2. ELISA IgG detection with rROP2 showed good agreement with assays performed with T. gondii extract, but rROP2 IgG avidity assays were unrelated to whole extract antigen IgG avidity, regardless of the chaotrope used. These data show that avidity maturation is specific to individual antigen prevalence and immune response during infection. ELISA rROP2 IgG assays may be an alternative serological test for the diagnosis of toxoplasmosis during pregnancy, although our data do not support their use in avidity assays.

Toxoplasmosis in pregnancy: determination of IgM, IgG and avidity in filter paper-embedded blood

OBJECTIVE

To detect immunoglobulin M (IgM) anti-Toxoplasma gondii antibodies and determine immunoglobulin G (IgG) titer and avidity in filter paper-embedded blood (FPEB) samples of pregnant women.

STUDY DESIGN

A total of 100 FPEB samples of pregnant women (30 positive and 70 negative) were analyzed for anti-T. gondii-specific IgM antibodies. Eleven and nine pairs of serum and FPEB samples were used to standardize IgG titration and avidity, respectively. Then, the correlation of avidity results was determined with 23 serum/FPEB pairs from IgG-positive cases.

RESULT

IgM detection in FPEB was 92% sensitive and 100% specific. The titration of IgG antibodies in FPEB correlated with that of serum (r >or=0.9). Significant difference in avidity between the acute and the undetermined/chronic cases was observed in both samples. As expected, no correlation was found between IgM levels and avidity.

CONCLUSION

The FPEB is useful to infer infection phase, and thus to speed clinical decisions in congenital toxoplasmosis management.

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.

Correlation between specific IgM levels and percentage IgG-class antibody avidity to Toxoplasma gondii

Toxoplasmosis is an usually asymptomatic worldwide disseminated infection. In its congenital presentation it may lead to abortion or fetal malformations. Antenatal evaluation is considered of paramount importance to identify seronegative women and allow for prophylaxis. Recent improvements in sensitivity of IgM tests has made IgM detection an extremely protracted acute phase marker, and IgG avidity evaluation test became necessary. Observation has shown that a correlation can be established between IgM levels and avidity percentages, suggesting that frequently the avidity test may not be necessary. In this study we analyzed Toxoplasma gondii IgM levels of 202 samples and their IgG avidity percentages, in order to define specific levels whose IgM quantification could by itself define serodiagnosis and therefore make the avidity evaluation unnecessary. We showed that for IgM levels below 2.0 and above 6.0 serodiagnosis of toxoplasmosis could be established without need of IgG avidity test. IgM levels between these two parameters are associated with varying avidity indexes highlighting the importance of its evaluation as a means to confirm toxoplasmosis. Following this demonstration it was possible to avoid the avidity test for 75% of the cases, to reduce the turnaround time and to reduce costs.

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.

Assessment of the value of detecting specific IgA antibodies for the diagnosis of a recently acquired primary Toxoplasma infection

OBJECTIVE

To assess the value of detecting IgA antibodies for the diagnosis of a recently acquired primary Toxoplasma infection.

METHODS

IgA antibodies were screened in sera from 87 women with different serological profiles of Toxoplasma gondii IgM and IgG antibodies and Toxoplasma-specific IgG avidity. The IgM and IgG antibodies and the IgG avidity were measured with an automated Vitek Immuno Diagnostic Assay System (VIDAS). Anti-T.gondii IgA was measured with Platelia Toxo IgA TMB kits.

RESULTS

All 12 sera obtained from women with clinical and/or serological evidence of a recently acquired Toxoplasma infection were positive for IgA. In 42 serum samples obtained more than 6 months after T. gondii infection from women with no clinical evidence of infection, but who had a positive IgM test and a high IgG avidity index, the IgA-enzyme linked immunosorbent assay (ELISA) test results were positive, negative, and doubtful in 16 (38.1%), 23 (54.8%), and 3 (7.1%) sera, respectively. In eight women, IgA was detected in sera collected more than 9 months after the onset of infection. The IgA test result was also positive in 11 of 12 sera (91.7%) obtained from women with no clinical evidence of toxoplasmosis, but who had a positive IgM test and a borderline IgG avidity index. The IgA-ELISA was negative in 21 sera obtained more than 2 years after the onset of T. gondii infection from women with no clinical evidence of toxoplasmosis, but who had a negative IgM test and a positive IgG test.

CONCLUSION

These results show that IgA is not a dependable marker for a recently acquired primary Toxoplasma infection.

IgG avidity assay firms up the diagnosis of acute toxoplasmosis on the first serum sample in immunocompetent pregnant women

Rapid diagnosis of acute toxoplasmosis during pregnancy permits timely treatment and prevents or attenuates congenital toxoplasmosis. Specific IgM antibodies to Toxoplasma as marker of acute infection are often poorly informative, meaning that a complementary technique is needed to reach a diagnosis on the first sample. Here we evaluated 2 commercial kits designed to assist with the diagnosis of acute toxoplasmosis: Platelia Toxo IgG Avidity Complementary Reagents and Platelia Toxo IgA, both from BIO-RAD (Marnes La Coquette, France). We tested 2 groups of subjects: 36 patients with acute toxoplasmosis and 55 patients with chronic toxoplasmosis. The IgG avidity test had a sensitivity of 100% (36/36), a specificity of 92.7% (51/55), a positive predictive value of 90%, and a negative predictive value of 100%. Among the immunocompetent women population, the avidity test had perfect sensitivity and specificity, and positive and negative predictive values of 100%. The IgA test had a sensitivity of 88.8% (32/36) and a specificity of 85.4% (47/55), and positive and negative predictive values of 80% and 92.1%, respectively. When the 2 tests were combined, there was only 1 case in which the diagnosis of chronic toxoplasmosis could not be confirmed. The IgG avidity test can therefore be used to rapidly distinguish between chronic and acute infection on the first sample from a pregnant woman, provided there is no underlying immunodepression and no ongoing antitoxoplasmic treatment. In these 2 situations, the results must be interpreted with care, and other serologic markers, including IgA, should be tested. Determination of a pregnant woman's status on a first serum sample allows therapeutic and preventive management to be started without delay.

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.