Novel interpretation of molecular diagnosis of congenital toxoplasmosis according to gestational age at the time of maternal infection

Molecular diagnosis of human toxoplasmosis: the state of the art

Toxoplasma gondii (T. gondii) is an obligate intracellular apicomplexan protozoan that causes toxoplasmosis. Approximately one-third of the world's population is currently T. gondii-seropositive. Although most infections are symptomless, a few can produce retinal lesions and, in immunocompromised persons or when congenitally contracted, can progress to life-threatening central nervous system disseminated infections. Therefore, quick, and precise diagnosis is a must. Molecular techniques nowadays play a crucial role in toxoplasmosis diagnosis, particularly in immunocompromised patients or congenital toxoplasmosis. This review aimed to detail recent advancements in molecular diagnostics of T. gondii infections. The terms "Toxoplasmosis," "Molecular diagnostics," "PCR," "qPCR," "B1," and "rep529" were used to search the English-language literature. In developed nations, conventional PCR (PCR) and nested PCR have been supplanted by quantitative PCR (qPCR), although they are still widely employed in poor nations. The diagnosis of toxoplasmosis has been revolutionized by the emergence of molecular diagnostics. Unfortunately, there is still substantial interlaboratory variability. There is an immediate need for standardization to increase the comparability of results between laboratories and clinical trials.

Graphical abstract

A graphical abstract highlighting the summary of Toxoplasma molecular diagnostics, created using Biorender.com.

Systematic Review and Meta-Analysis of Congenital Toxoplasmosis Diagnosis: Advances and Challenges

Objective

To understand how congenital toxoplasmosis (CT) diagnosis has evolved over the years, we performed a systematic review and meta-analysis to summarize the kind of analysis that has been employed for CT diagnosis.

Methods

PubMed and Lilacs databases were used in order to access the kind of analysis that has been employed for CT diagnosis in several samples. Our search combined the following combining terms: "congenital toxoplasmosis" or "gestational toxoplasmosis" and "diagnosis" and "blood," "serum," "amniotic fluid," "placenta," or "colostrum." We extracted data on true positive, true negative, false positive, and false negative to generate pooled sensitivity, specificity, and diagnostic odds ratio (DOR). Random-effects models using MetaDTA were used for analysis.

Results

Sixty-five articles were included in the study aiming for comparisons (75.4%), diagnosis performance (52.3%), diagnosis improvement (32.3%), or to distinguish acute/chronic infection phases (36.9%). Amniotic fluid (AF) and placenta were used in 36.9% and 10.8% of articles, respectively, targeting parasites and/or T. gondii DNA. Blood was used in 86% of articles for enzymatic assays. Colostrum was used in one article to search for antibodies. In meta-analysis, PCR in AF showed the best performance for CT diagnosis based on the highest summary sensitivity (85.1%) and specificity (99.7%) added to lower magnitude heterogeneity.

Conclusion

Most of the assays being researched to diagnose CT are basically the same traditional approaches available for clinical purposes. The range in diagnostic performance and the challenges imposed by CT diagnosis indicate the need to better explore pregnancy samples in search of new possibilities for diagnostic tools. Exploring immunological markers and using bioinformatics tools and T. gondii recombinant antigens should address the research needed for a new generation of diagnostic tools to face these challenges.

Exploring the potential of Toxoplasma gondii in drug development and as a delivery system

Immune-mediated inflammatory diseases are various groups of conditions that result in immune system disorders and increased cancer risk. Despite the identification of causative cytokines and pathways, current clinical treatment for immune-mediated inflammatory diseases is limited. In addition, immune-mediated inflammatory disease treatment can increase the risk of cancer. Several previous studies have demonstrated that Toxoplasma gondii manipulates the immune response by inhibiting or stimulating cytokines, suggesting the potential for controlling and maintaining a balanced immune system. Additionally, T. gondii also has the unique characteristic of being a so-called "Trojan horse" bacterium that can be used as a drug delivery system to treat regions that have been resistant to previous drug delivery therapies. In this study, we reviewed the potential of T. gondii in drug development and as a delivery system through current research on inflammation-regulating mechanisms in immune-mediated inflammatory diseases.

Toxoplasma gondii Infection in Pregnancy - Recommendations of the Working Group on Obstetrics and Prenatal Medicine (AGG - Section on Maternal Disorders)

Aim The AGG (Working Group for Obstetrics and Prenatal Diagnostics, Section Maternal Diseases) has issued these recommendations to improve the detection and management of Toxoplasma gondii infection in pregnancy. Methods Members of the Task Force developed the recommendations and statements presented here using recently published literature. The recommendations were adopted after a consensus process by members of the working group. Recommendations This article focuses on the epidemiology and pathophysiology of Toxoplasma gondii infection in pregnancy and includes recommendations for maternal and fetal diagnosis, transmission prophylaxis, therapy, prevention, screening, and peripartum management.

Molecular Diagnosis of Toxoplasmosis: Multicenter Evaluation of the Toxoplasma RealCycler Universal PCR Assay on 168 Characterized Human Samples

Real-time PCR plays a crucial role in the diagnosis of toxoplasmosis. In this multicenter study, the Toxoplasma RealCycler Universal assay was assessed for the diagnosis of toxoplasmosis by eight reference laboratories. DNAs from diverse clinical samples were included: 141 characterized samples from patients with different clinical forms of proven toxoplasmosis and 27 from patients without toxoplasmosis were tested in duplicate with the commercial assay. Final diagnosis was affirmed by each center by analysis of clinical settings and biological follow-up. Calibrated Toxoplasma gondii standards and 11 external quality control samples were also included. Discrepant results observed after the first run of commercial PCR were controlled by both reference and commercial PCR assays. Using the commercial assay, the detection threshold varied from 0.01 to 1 tachyzoites/mL, depending on the center. The relationship between crossing point and DNA concentration was linear over 4 log units (r² > 0.99), and PCR efficiencies were satisfactory (89% to 104%). The results of the 11 external quality control samples were concordant after one retesting, but those for 3 clinical samples remained discrepant. Sensitivity and specificity were calculated at 97.8% (95% CI, 97.8%-100%) and 100% (95% CI, 87.2%-100%), respectively. Provided that PCRs are performed at least in duplicate to detect low parasitic loads, Toxoplasma RealCycler Universal PCR showed suitable performances to diagnose the different forms of toxoplasmosis.

Diagnosis of Congenital Toxoplasmosis: No Benefit of IgA Antibody Detection by Platelia ELISA in a Tricentric Evaluation

The diagnostic accuracy of a commercial Toxoplasma gondii IgA antibody enzyme-linked immunosorbent assay (ELISA) was evaluated in the context of routine practice on 289 newborns with congenital toxoplasmosis (CT) and 220 healthy controls. The performance of this assay was compared to that of the current gold-standard test for anti- Toxoplasma IgM detection, an immunosorbent agglutination assay (ISAGA).

Molecular detection of Toxoplasma gondii in placentas of women who received therapy during gestation in a toxoplasmosis outbreak

Toxoplasmosis is a disease caused by T. gondii, a protozoa which affects humans and animals and is widely distributed worldwide. In humans, there is great concern due to the serious consequences that can occur in the infection of pregnant women and the newborn. The early diagnosis of gestational toxoplasmosis is important for treatment to be carried out in order to prevent vertical transmission or reduce damage. The diagnosis can be made through the detection of antibodies in pregnant women or neonates and PCR of amniotic fluid. Previous studies have also reported PCR of the placenta as a good diagnostic test. Our study evaluated the detection of T. gondii DNA in placenta samples from parturients seen at the University Hospital of Santa Maria, Southern Brazil and treated during the pregnancy. We performed PCR in forty samples and five were positive, representing 12.5%. When correlating the treatment time and the detection of DNA in the placentas, no significant result was found. The prevalence of positive samples was lower than in other studies in the literature. The data reaffirm the importance of carrying out the analysis of the placenta.

Molecular diagnosis of toxoplasmosis: recent advances and a look to the future

INTRODUCTION

Toxoplasmosis is a globally distributed parasitic infection that can be particularly severe when opportunistic or congenital. Its diagnosis requires accurate and rapid techniques that rely mainly on serology and molecular methods.

AREAS COVERED

The aim of this review was to discuss the positioning of the molecular diagnosis of toxoplasmosis according to the different clinical situations possibly resulting from infection with T. gondii, and to detail recent developments in this technique. The English and French literature were searched with the following keywords: 'Toxoplasmosis', "Molecular diagnosis" and 'PCR'.

EXPERT OPINION

Molecular techniques have revolutionized the diagnosis of toxoplasmosis, and practices have considerably evolved over the past decades. However, there is still a high degree of inter-laboratory heterogeneity which impairs comparisons between results and studies. Efforts to standardize practices are underway.

Multicenter Comparative Assessment of the TIB MolBiol Toxoplasma gondii Detection Kit and Four Laboratory-Developed PCR Assays for Molecular Diagnosis of Toxoplasmosis

Toxoplasmosis can be a life-threatening infection, particularly during pregnancy and in immunocompromised patients. The biological diagnosis of toxoplasmosis is challenging and has been revolutionized by molecular detection methods. This article summarizes the data of a multicenter study involving four centers to assess the performances of a commercial PCR assay as compared with four in-house PCR assays using Toxoplasma gondii standards, 20 external quality control specimens, and 133 clinical samples. This clinical cohort includes well-characterized clinical samples corresponding to different clinical situations: confirmed congenital toxoplasmosis (44 samples), toxoplasmosis in immunocompromised patients (25 samples), and chorioretinitis (5 samples). Furthermore, 59 samples from patients without toxoplasmosis were included as negative controls. The analytical sensitivities of the five methods tested were very similar; and the limit of Toxoplasma DNA detection was around 0.01 T. gondii genome per reaction for all the methods. The overall concordance between the commercial PCR and the four in-house PCR assays was 97.7% (130/133). The clinical sensitivity and specificity were >98% and could be increased for the commercial kit when PCR was performed in multiplicate to detect low parasitic loads. In conclusion, the commercial PCR assay shows suitable performances to diagnose the different clinical forms of toxoplasmosis.

Impact of pre-analytic step duration on molecular diagnosis of toxoplasmosis for five types of biological samples

Introduction

Toxoplasma-PCR is essential to diagnose ocular, cerebral, disseminated and congenital toxoplasmosis. This multicenter study evaluated the impact of sample storage duration at +4°C on PCR assay performances in order to propose guidelines for the storage of samples during shipment or/and before PCR.

Materials and methods

Five matrices, amniotic (AF), cerebrospinal (CSF), and bronchoalveolar lavage fluids (BALF), whole blood (WB) and buffy coat (BC), were artificially spiked with different amounts of Toxoplasma gondii (20, 100, 500 tachyzoites per mL of sample) or with previously infected THP1 cells. DNA extractions were performed at day 0 and after 2, 4 and 7 days of storage at +4°C. Each extract was amplified at least twice by real-time PCR.

Results

A total of 252 spiked samples was studied. No increase of crossing point was observed and all samples were positive for AF, BALF, BC and infected THP1-spiked WB after up to 7 days at 4°C. For CSF spiked with 20 parasites/mL, only 50% of PCR reactions were positive at D7 (p<0.05). For WB spiked with type II parasites, all reactions remained positive at D7 but amplifications were significantly delayed from D2; and for WB spiked with RH strain, the proportion of positive reactions decreased at D7.

Conclusion

The storage of clinical samples at +4°C is compatible with the molecular detection of T. gondii parasites. Provided that PCR assays are performed in duplicate, storage of samples is possible up to 7 days. However, from the fifth day onwards, and for samples susceptible to contain low parasitic loads, we recommend to perform the PCR in multiplicate.

Seroprevalence and risk factors of Toxoplasma gondii infection in women with recurrent fetal loss from the province of Khyber Pakhtunkhwa, Pakistan

BACKGROUND

In women with a bad obstetric history (BOH), infection is an established cause of recurrent fetal loss. A common infecting agent is the protozoan parasite Toxoplasma gondii (T. gondii). The aim of this study was to measure the prevalence of toxoplasmosis in women with recurrent fetal loss from the Khyber Pakhtunkhwa province of Pakistan.

METHODS

The study included 360 females aged 16-40 years, of which 180 had a bad obstetric history (study group) and the other 180 had no such history (control group). Blood serum samples were tested for toxoplasma IgM antibodies by Enzyme Linked Immunosorbent Assay and for toxoplasma IgG antibodies using an Immunochromatographic technique.

RESULTS

The overall seroprevalence of toxoplasma infection in study group females was 40.6% and in control group females it was 7.2%. Specifically, IgM prevalence was 12.8% in the study group and 1.1% in the control group. IgG prevalence was 23.9% in the study group and 6.1% in the control group. IgM and IgG combined prevalence was 3.9% in the study group cases. There is a statistically significant association between BOH and seropositivity for T. gondii (p < 0.0001, Chi square test). Various risk factors associated with T. gondii seroprevalence in study and control groups were analyzed.

CONCLUSION

The seroprevalence of toxoplasmosis was significantly higher in women with a bad obstetric history compared to those with no such history. Associated risk factors had no significant effects on the results.

Congenital toxoplasmosis: What is the evidence for chemoprophylaxis to prevent fetal infection?

Although prenatal diagnosis and prenatal and neonatal therapy of congenital toxoplasmosis are available, there is controversy concerning the effectiveness of prophylaxis to prevent placental transmission. Experimental, parasitological, and clinical data suggest a "window of opportunity" following maternal infection. Among medications active against Toxoplasma gondii, mainly spiramycin (Spy) and pyrimethamine + sulfonamide combinations (P-S) have been evaluated. Results from observational studies suffered treatment bias, since prescriptions differed according to the gestational age at seroconversion, which is the major risk factor for transmission, and many lacked precise timing. Some large retrospective studies found no difference in transmission according to prophylactic treatment, but transmission was lower when treatment started promptly after maternal seroconversion. A few recent studies adjusting for timing of infection observed lower transmission in case of P-S than other or no prophylaxis. In the only randomized controlled trial, transmission was lower with P-S than S (18.5% vs 30%, P = .147); this association was strengthened when the treatment was started within 3 weeks of seroconversion, and the incidence of fetal cerebral ultrasound signs was significantly reduced in the P-S group. Rapid initiation of prophylactic therapy following maternal infection, which is usually asymptomatic, requires systematic screening for maternal seroconversion during pregnancy.

Inhibition of polymerase chain reaction: Pathogen-specific controls are better than human gene amplification

PCR inhibition is frequent in medical microbiology routine practice and may lead to false-negative results; however there is no consensus on how to detect it. Pathogen-specific and human gene amplifications are widely used to detect PCR inhibition. We aimed at comparing the value of PCR inhibitor detection using these two methods. We analysed Cp shifts (ΔCp) obtained from qPCRs targeting either the albumin gene or the pathogen-specific sequence used in two laboratory-developed microbiological qPCR assays. 3152 samples including various matrixes were included. Pathogen-specific amplification and albumin qPCR identified 62/3152 samples (2.0%), and 409/3152 (13.0%) samples, respectively, as inhibited. Only 16 samples were detected using both methods. In addition, the use of the Youden's index failed to determine adequate Cp thresholds for albumin qPCR, even when we distinguished among the different sample matrixes. qPCR targeting the albumin gene therefore appears not adequate to identify the presence of PCR inhibitors in microbiological PCR assays. Our data may be extrapolated to other heterologous targets and should discourage their use to assess the presence of PCR inhibition in microbiological PCR assays.

Risk of congenital toxoplasmosis in women with low or indeterminate anti-Toxoplasma IgG avidity index in the first trimester of pregnancy: an observational retrospective study

OBJECTIVES

Congenital toxoplasmosis (CT) affects one to ten fetuses per 10 000 live newborns in western countries. Without knowing pre-conception serostatus, it is hard to date the infection when anti-Toxoplasma IgG and IgM antibodies are positive at first screening. Although a high IgG avidity index (AI) in the first trimester excludes CT, the same cannot be said of intermediate and low AI. The aim of this study was to estimate the risk of CT when intermediate or low AI is detected in the first trimester of pregnancy.

METHODS

Our observational retrospective study enrolled women with positive anti-Toxoplasma IgG and IgM, and low/intermediate AI in the first trimester of gestation seen at two reference centres in northern Italy between 2006 and 2015. All women received spiramycin. When requested by women, a sample of fluid obtained through amniocentesis was tested with a commercial real-time PCR. CT was defined by positive PCR result confirmed on aborted materials or by newborn follow up.

RESULTS

Overall, 778 first-trimester pregnant women were included; AI was low in 532/778 (68%) and intermediate in 246/778 (32%). Amniocenteses were performed in 528/778 (67.9%), with no fetal loss. In all, 19/778 (2.4%) miscarriages and 15/778 (1.9%) pregnancy terminations were recorded; 9/778 (1.6%) were lost to follow up. In two women, PCR on amniotic fluid was positive, but CT was confirmed in only 1/747 cases (0.13%, 95% CI 0.02%-0.75%).

CONCLUSION

In our study, the risk of CT was much lower than anticipated. These data must be considered when counselling these women.

Evaluation of Toxoplasma gondii B1 gene in Placental Tissues of Pregnant Women with Acute Toxoplasmosis

Background:

One of the consequences of toxoplasmosis is the risk of passing it from mother to fetus and the onset of congenital toxoplasmosis during pregnancy. The purpose of this study was to evaluate the B1 gene of Toxoplasma gondii in the placental tissues of pregnant women with acute toxoplasmosis.

Materials and Methods:

The study was a cross-sectional study. Serum samples of pregnant women who attended to Fatemieh Hospital of Hamadan University of Medical Sciences were tested for immunoglobulin G (IgG) antibodies against T. gondii by enzyme-linked immunosorbent assay. Then, polymerase chain reaction was used to identify the specific B1 gene of T. gondii in IgG seropositive women. The placental tissues of the pregnant women with positive serum B1 gene examined for this gene. Anti-Toxoplasma immunoglobulin M (IgM) was performed on the umbilical cord and neonate blood.

Results:

Anti-Toxoplasma IgG was detected in 167 out of 653 (25.6%) pregnant women. T. gondii B1 gene was identified in 36 out of 167 (21.6%) of IgG seropositive women. After delivery, the B1 gene was evaluated in 15 out of 36 (41.7%) patients’ placental tissues, 13 of which were positive for this gene (86.7%). Anti-Toxoplasma IgM was detected neither in any umbilical cord nor in neonatal blood samples. All newborns, with the exception of one case, were born with normal birth weight and in term birth.

Conclusion:

The B1 gene was detected in 86.7% of the placental tissue of women who were involved in acute toxoplasmosis during pregnancy.

A new LAMP-based assay for the molecular diagnosis of toxoplasmosis: comparison with a proficient PCR assay

Toxoplasmosis is generally a benign infection caused by the protozoan parasite Toxoplasma gondii but can have severe consequences in fetuses of mothers infected during pregnancy (congenital toxoplasmosis) and immunocompromised individuals. PCR-based diagnostic tests have become crucial for its diagnosis. However, this molecular diagnosis essentially relies upon laboratory-developed methods and suffers from a lack of standardization, leading to great variation in methods and performance among laboratories. With the need for accreditation of clinical microbiological laboratories, the use of commercial PCR kits has become an attractive alternative; but thorough evaluation of newly commercialized kits by proficient groups is necessary before any recommendation can be made to parasitology laboratories by health authorities or learned societies. Here, we compared the performance of an original commercial method, the Iam TOXO Q-LAMP (DiaSorin®), using Loop-mediated isothermal amplification (LAMP) technology, with our reference laboratory-developed method using real-time PCR. The kit was first tested using amniotic fluid (AF) and plasma samples (either negative or spiked with live T. gondii tachyzoites at different concentrations (from 7 to 10⁵ tachyzoites/mL)). It was then assessed using a cohort of 11 AF, five placental and 32 blood clinical samples preserved at -20 °C. For the processing of placental/blood samples, a pretreatment step was used, which did not strictly follow the manufacturer's recommendations. The practical ease of use and compliance with good laboratory practices were also evaluated. Although the LAMP assay was less sensitive than the laboratory-developed method at very low parasite concentrations (0.1 T. gondii genome equivalents/mL), the two methods yielded identical results qualitatively and, in some instances, quantitatively, particularly for AF samples.

Toxoplasmosis: Seroprevalence in pregnant women, and serological and molecular screening in neonatal umbilical cord blood

Toxoplasmosis is a common zoonotic disease that can also be transmitted from the mother to the embryo, with the risk of congenital infection varying around the world. The aim of this study was to screen pregnant women and their neonates for toxoplasmosis by serologic and molecular methods and assess the impact of risk factors associated with toxoplasmosis on the rate of congenital infection. This study was conducted at a regional maternity hospital in Arak, the capital of the Markazi Province in Iran, during a period of six months. All selected pregnant women (n=261) and the corresponding cord blood samples were serologically screened for toxoplasmosis, with seropositive samples also undergoing molecular testing. Demographic data, as well as information related to the risk factors associated with the transmission of the disease, were collected from mothers and their neonates. The detection of anti-Toxoplasma antibodies and the extraction of DNA from blood samples were conducted using commercial kits. Results showed that the sera of 87 maternal blood samples (33.3%) and 40 cord blood samples (15.3%) were positive for anti-Toxoplasma antibodies (IgG and/or IgM). Molecular screening of the seropositive samples only identified one positive cord blood sample. In other words, the diagnosis of congenital toxoplasmosis was definitive in only one neonate. There was no significant association between the risk of parasite transmission and neonatal seropositivity (p >0.05). Therefore, the results showed that the prevalence of congenital toxoplasmosis in the studied area was consistent with the global rate and suggest that the implementation of newborn screening and follow-up testing could help reduce the disease risk.

Role of vertical transmission of Toxoplasma gondii in prevalence of infection

The parasite, Toxoplasma gondii, is a highly successful pathogen that infects around 30% of the global human population. Additionally, it is able to infect all warm blooded animals with high prevalence. This is surprising as it is a parasite of the cat and can only complete its full sexual cycle in that host. This review examines the important key routes of transmission: infective oocysts from the cat, ingestion of raw infected tissue and vertical transmission. The latter route of transmission has traditionally been thought to be rare. In this review, this assumption is examined and discussed in the light of the current literature. The available evidence points to the possibility that vertical transmission occurs frequently in natural populations of mice however the evidence in sheep is currently ambivalent and controversial. In humans, the situation appears as though vertical transmission may be rare although there is still much that is unexplained.

Molecular diagnosis of Toxoplasma gondii infection in Libya

Background

Toxoplasma gondii infections are prevalent in humans and animals throughout Libya. Current diagnosis is based on detection of Toxoplasma-specific IgM and IgG. In this study, we established and optimized a diagnostic PCR assay for molecular diagnosis of T. gondii in Libya.

Methods

From January to December, 2010, 177 blood and serum samples were collected from suspected patients. This includes: 140 women who have had spontaneous abortions, 26 HIV-positive patients, nine patients with leukemia and lymphoma, and two infants with ocular infection. Samples were screened for anti-Toxoplasma IgG and IgM antibodies before DNA extraction. The surface antigen gene 2 (SAG2) was targeted in a semi-nested PCR to amplify a 999 bp and a 614 bp fragment in the first and the second run respectively.

Results

A total of 54/140 (38.5 %) women who have had spontaneous abortions, 23/26 (88 %) HIV patients, 6/9 (66.6 %) of the leukaemia and lymphoma patients, and one child with ocular infection were seropositive for anti-Toxoplasma IgG and/or IgM. Genomic DNA was extracted from 38 selected seropositive samples. The PCR was sensitive enough to detect DNA concentration of 12 ng/μL. PCR analysis was performed for 38 selected seropositive patients (16 women who have had spontaneous abortions, 15 positive HIV patients, six leukaemia patients and one child with ocular infection). Our designed primers were successfully amplified in 22/38 (57.9 %) samples; 5/12 (35.7 %) from serum and 17/26 (65.8 %) from whole blood samples. All PCR positive samples were IgG-positive except two samples which were IgM and IgG & IgM-positive serum samples respectively. The semi-nested PCR confirmed five more samples. These included two leukaemia and two HIV-positive whole blood samples and one serum sample from an aborted woman.

Conclusion

The ability of PCR to diagnose active toxoplasmosis is needed in immunocompromised patients and congenital toxoplasmosis cases, especially when serological techniques fail. For the first time in Libya, we established and optimized semi-nested PCR of SAG2 gene. The developed PCR method was able to detect as little as 12 ng/μL of T. gondii DNA and was useful to diagnose the diseases in women who have had spontaneous abortions, HIV-positive patients, patients with leukemia and lymphoma, and infants with ocular infection.

Performance of Polymerase Chain Reaction Analysis of the Amniotic Fluid of Pregnant Women for Diagnosis of Congenital Toxoplasmosis: A Systematic Review and Meta-Analysis

Introduction

Congenital infection caused by Toxoplasma gondii can cause serious damage that can be diagnosed in utero or at birth, although most infants are asymptomatic at birth. Prenatal diagnosis of congenital toxoplasmosis considerably improves the prognosis and outcome for infected infants. For this reason, an assay for the quick, sensitive, and safe diagnosis of fetal toxoplasmosis is desirable.

Goal

To systematically review the performance of polymerase chain reaction (PCR) analysis of the amniotic fluid of pregnant women with recent serological toxoplasmosis diagnoses for the diagnosis of fetal toxoplasmosis.

Method

A systematic literature review was conducted via a search of electronic databases; the literature included primary studies of the diagnostic accuracy of PCR analysis of amniotic fluid from pregnant women who seroconverted during pregnancy. The PCR test was compared to a gold standard for diagnosis.

Results

A total of 1.269 summaries were obtained from the electronic database and reviewed, and 20 studies, comprising 4.171 samples, met the established inclusion criteria and were included in the review. The following results were obtained: studies about PCR assays for fetal toxoplasmosis are generally susceptible to bias; reports of the tests’ use lack critical information; the protocols varied among studies; the heterogeneity among studies was concentrated in the tests’ sensitivity; there was evidence that the sensitivity of the tests increases with time, as represented by the trimester; and there was more heterogeneity among studies in which there was more time between maternal diagnosis and fetal testing. The sensitivity of the method, if performed up to five weeks after maternal diagnosis, was 87% and specificity was 99%.

Conclusion

The global sensitivity heterogeneity of the PCR test in this review was 66.5% (I²). The tests show low evidence of heterogeneity with a sensitivity of 87% and specificity of 99% when performed up to five weeks after maternal diagnosis. The test has a known performance and could be recommended for use up to five weeks after maternal diagnosis, when there is suspicion of fetal toxoplasmosis.

HLA-DQA1/B1 alleles as putative susceptibility markers in congenital toxoplasmosis

Host and parasite genotypes are among the factors associated with congenital toxoplasmosis pathogenesis. As HLA class II molecules play a key role in the immune system regulation, the aim of this study was to investigate whether HLA-DQA1/B1 alleles are associated with susceptibility or protection to congenital toxoplasmosis. One hundred and twenty-two fetuses with and 103 without toxoplasmosis were studied. The two study groups were comparable according to a number of socio-demographic and genetic variables. HLA alleles were typed by PCR-SSP. In the HLA-DQA1 region, the allele frequencies showed that *01:03 and *03:02 alleles could confer susceptibility (OR= 3.06, p = 0.0002 and OR= 9.60, p= 0.0001, respectively) as they were more frequent among infected fetuses. Regarding the HLA-DQB1 region, the *05:04 allele could confer susceptibility (OR = 6.95, p < 0.0001). Of the 122 infected fetuses, 10 presented susceptibility haplotypes contrasting with only one in the non-infected group. This difference was not statistically significant after correction for multiple comparison (OR = 9.37, p=0.011). In the casuistic, there were two severely damaged fetuses with high parasite loads determined in amniotic fluid samples and HLA-DQA1 susceptibility alleles. In the present study, a discriminatory potential of HLA-DQA1/B1 alleles to identify susceptibility to congenital toxoplasmosis and the most severe cases has been shown.

Molecular diagnosis of toxoplasmosis in immunocompromised patients: a 3-year multicenter retrospective study

Toxoplasmosis is a life-threatening infection in immunocompromised patients (ICPs). The definitive diagnosis relies on parasite DNA detection, but little is known about the incidence and burden of disease in HIV-negative patients. A 3-year retrospective study was conducted in 15 reference laboratories from the network of the French National Reference Center for Toxoplasmosis, in order to record the frequency of Toxoplasma gondii DNA detection in ICPs and to review the molecular methods used for diagnosis and the prevention measures implemented in transplant patients. During the study period, of 31,640 PCRs performed on samples from ICPs, 610 were positive (323 patients). Blood (n = 337 samples), cerebrospinal fluid (n = 101 samples), and aqueous humor (n = 100 samples) were more frequently positive. Chemoprophylaxis schemes in transplant patients differed between centers. PCR follow-up of allogeneic hematopoietic stem cell transplant (allo-HSCT) patients was implemented in 8/15 centers. Data from 180 patients (13 centers) were further analyzed regarding clinical setting and outcome. Only 68/180 (38%) patients were HIV(+); the remaining 62% consisted of 72 HSCT, 14 solid organ transplant, and 26 miscellaneous immunodeficiency patients. Cerebral toxoplasmosis and disseminated toxoplasmosis were most frequently observed in HIV and transplant patients, respectively. Of 72 allo-HSCT patients with a positive PCR result, 23 were asymptomatic; all were diagnosed in centers performing systematic blood PCR follow-up, and they received specific treatment. Overall survival of allo-HSCT patients at 2 months was better in centers with PCR follow-up than in other centers (P < 0.01). This study provides updated data on the frequency of toxoplasmosis in HIV-negative ICPs and suggests that regular PCR follow-up of allo-HSCT patients could guide preemptive treatment and improve outcome.

Contribution of neonatal amniotic fluid testing to diagnosis of congenital toxoplasmosis

We evaluated the molecular diagnosis of congenital toxoplasmosis (CT) on neonatal amniotic fluid samples from 488 mother-child pairs. Maternal infection during pregnancy was diagnosed and dated or could not be ruled out. Forty-six cases of CT were defined according to the European Research Network on CT classification system and case definitions. Neonatal amniotic fluid testing had an overall sensitivity of 54% (95% confidence interval [95% CI], 39 to 69%) and a specificity of 100% (95% CI, 99 to 100%). Its sensitivity was 33% (95% CI, 13 to 59%) when antenatal diagnosis was positive and 68% (95% CI, 48 to 84%) when antenatal diagnosis was negative or lacking. This difference in sensitivity may have been due to treatment of antenatally diagnosed cases. Relative to postnatal serology, neonatal amniotic fluid testing allowed an earlier diagnosis to be made in 26% of the cases (95% CI, 9 to 51%).

A 10-year retrospective comparison of two target sequences, REP-529 and B1, for Toxoplasma gondii detection by quantitative PCR

This study aimed to evaluate the repeated sequence REP-529 compared to that of the B1 gene in the molecular diagnosis of toxoplasmosis by quantitative PCR (qPCR) in routine diagnosis. Over a 10-year period (2003 to 2013), all patients prospectively diagnosed with a positive REP-529 qPCR result for toxoplasmosis were included. All DNA samples (76 samples from 56 patients) were simultaneously tested using the two qPCR methods (REP-529 and B1). The mean cycle threshold (CT) obtained with the B1 qPCR was significantly higher (+4.71 cycles) than that obtained with REP-529 qPCR (P<0.0001). Thirty-one out of 69 extracts (45.6%) positive with REP-529 qPCR were not amplified with the B1 qPCR (relative sensitivity of 54.4% compared to that with REP-529), yielding false-negative results with 15/28 placenta, 5 cord blood, 2 amniotic fluid, 4 cerebrospinal fluid, 1 aqueous humor, 2 lymph node puncture, and 1 abortion product sample. This defect in sensitivity would have left 20/56 patients undiagnosed, distributed as follows: 12/40 congenital toxoplasmosis, 4/5 cerebral toxoplasmosis, 2/8 patients with retinochoroiditis, and 2 patients with chronic lymphadenopathy. This poor performance of B1 qPCR might be related to low parasite loads, since the mean Toxoplasma quantification in extracts with B1 false-negative results was 0.4 parasite/reaction. These results clearly show the superiority of the REP-529 sequence in the diagnosis of toxoplasmosis by PCR and suggest that this target should be adopted as part of the standardization of the PCR assay.

Amniocentesis for the detection of congenital toxoplasmosis: results from the nationwide Austrian prenatal screening program

Prenatal diagnosis of congenital toxoplasmosis (CT) influences therapeutical management in pregnant women and their offspring. In Austria, a nationwide serological healthcare program to identify potential maternal toxoplasma infections during pregnancy exists. We assessed the clinical use of amniocentesis for toxoplasma-specific polymerase chain reaction (PCR) on amniotic fluid to detect CT. Data on serology, amniocentesis, PCR, complications, treatment, and paediatric clinical outcome were collected retrospectively among the birth cohort 1992-2008. There were 1386 women with amniocentesis, but only in 707 cases (51%) was acute maternal infection confirmed serologically. A high proportion (49%) of amniocenteses with negative PCR results in women with chronic infection or seronegativity were performed without clinical justification for the women or their foetuses. The positive and negative predictive values of PCR were 94.4% and 99.3%, respectively. Thirty-nine foetuses with CT, including four deaths, were reported. The five PCR-negative but infected infants were identified by the serological and clinical follow-up program. Thirty percent of amniocenteses were performed in the third trimester, and gestational age or treatment did not influence PCR sensitivity. Amniocentesis is indicated in women with acute maternal infection, and facilitated targeted therapies in pregnant women and their offspring. In women with late toxoplasma infection, negative amniotic fluid PCR made treatment of infants unnecessary. Serological and clinical follow-up of infants is important to confirm the infection status of the infant. Recommendations, based on our 17-year experience, to improve the current diagnostic strategies and to reduce unnecessary amniocentesis, are given.

Multicentric comparative assessment of the bio-evolution Toxoplasma gondii detection kit with eight laboratory-developed PCR assays for molecular diagnosis of congenital toxoplasmosis

The detection of Toxoplasma gondii in amniotic fluid is an essential tool for the prenatal diagnosis of congenital toxoplasmosis and is currently essentially based on the use of PCR. Although some consensus is emerging, this molecular diagnosis suffers from a lack of standardization and an extreme diversity of laboratory-developed methods. Commercial kits for the detection of T. gondii by PCR were recently developed and offer certain advantages; however, they must be assessed in comparison with optimized reference PCR assays. The present multicentric study aimed to compare the performances of the Bio-Evolution T. gondii detection kit and laboratory-developed PCR assays set up in eight proficient centers in France. The study compared 157 amniotic fluid samples and found concordances of 99% and 100% using 76 T. gondii-infected samples and 81 uninfected samples, respectively. Moreover, taking into account the classification of the European Research Network on Congenital Toxoplasmosis, the overall diagnostic sensitivity of all assays was identical and calculated to be 86% (54/63); specificity was 100% for all assays. Finally, the relative quantification results were in good agreement between the kit and the laboratory-developed assays. The good performances of this commercial kit are probably in part linked to the use of a number of good practices: detection in multiplicate, amplification of the repetitive DNA target rep529, and the use of an internal control for the detection of PCR inhibitors. The only drawbacks noted at the time of the study were the absence of uracil-N-glycosylase and small defects in the reliability of the production of different reagents.

Characterization and multicentric validation of a common standard for Toxoplasma gondii detection using nucleic acid amplification assays

The molecular diagnosis of toxoplasmosis essentially relies upon laboratory-developed methods and suffers from lack of standardization, hence the large diversity of performances between laboratories. Moreover, quantifications of parasitic loads differ among centers, a fact which prevents the possible prediction of the severity of this disease as a function of parasitic loads. The objectives of this multicentric study performed in eight proficient laboratories of the Molecular Biology Pole of the French National Reference Center for Toxoplasmosis (NRC-T) were (i) to assess the suitability of a lyophilized preparation of Toxoplasma gondii as a common standard for use in this PCR-based molecular diagnosis and (ii) to make this standard available to the community. High-quality written procedures were used for the production and qualification of this standard. Three independent batches of this standard, containing concentrations ranging from 10(4) to 0.01 T. gondii genome equivalents per PCR, were first assessed: the linear dynamic range was ≥ 6 log, the intra-assay coefficients of variation (CV) from a sample containing 10 T. gondii organisms per PCR were 0.3% to 0.42%, and the interassay CV over a 2-week period was 0.76% to 1.47%. A further assessment in eight diagnostic centers showed that the standard is stable, robust, and reliable. These lyophilized standards can easily be produced at a larger scale when needed and can be made widely available at the national level. To our knowledge, this is the first quality control assessment of a common standard which is usable both for self-evaluation in laboratories and for accurate quantification of parasitic loads in T. gondii prenatal infections.

Assessment of laboratory methods used in the diagnosis of congenital toxoplasmosis after maternal treatment with spiramycin in pregnancy

BACKGROUND

The different laboratory methods used in the diagnosis of congenital toxoplasmosis have variable sensitivity and specificity. There is no evidence to prove that maternal treatment reduces the risk of fetal infection. The purpose of this study was to assess methods for the confirmation of congenital toxoplasmosis after maternal treatment with spiramycin during pregnancy, and to evaluate the effect of this treatment on clinical manifestations of the disease in newborns (NB).

METHODS

This was a community-based, cross-sectional study of acute toxoplasmosis in newborns at risk of acquiring congenital infection. Participating newborns were born in the Clinical Hospital Maternity Ward of the Federal University of Goiás. Eligible participants were divided into 2 groups: group 1 consisted of 44 newborns born to mothers treated with spiramycin during pregnancy and group 2 consisted of 24 newborns born to mothers not treated with spiramycin during pregnancy because the diagnosis of toxoplasmosis was not performed. The sensitivity and specifity of PCR for T. gondii DNA in peripheral blood and serological testing for specific anti-T. gondii IgM and IgA, and the effects of maternal spiramycin treatment on these parameters, were determined by associating test results with clinical manifestations of disease.

RESULTS

The sensitivity of the markers (T. gondii DNA detected by PCR, and the presence of specific anti-T. gondii IgM and IgA) for congenital toxoplasmosis was higher in group 2 than in group 1 (31.6, 68.4, 36.8% and 3.7, 25.9, 11.1% respectively). Even with a low PCR sensitivity, the group 2 results indicate the importance of developing new techniques for the diagnosis of congenital toxoplasmosis in newborns. Within group 1, 70.4% of the infected newborns were asymptomatic and, in group 2, 68.4% showed clinical manifestations of congenital toxoplasmosis.

CONCLUSIONS

The higher proportion of infants without clinical symptoms in group 1 (70.4%) suggests the maternal treatment with spiramycin delays fetal infection, reducing the clinical sequelae of the disease in newborns. Given the low sensitivity of the tests used, when there is suspicion of congenital transmission several serological and parasitological tests are required in order to confirm or exclude congenital toxoplasmosis in newborns.

Polymerase chain reaction in cerebrospinal fluid for the diagnosis of congenital toxoplasmosis

BACKGROUND

Congenital toxoplasmosis can result in visual impairment, hearing loss, serious neurologic sequelae and death in the infant. We studied the potential of the polymerase chain reaction (PCR) in cerebrospinal fluid (CSF) for diagnosis of congenital toxoplasmosis.

METHODS

For this purpose, we studied both congenitally infected (diagnosed clinically and serologically) and noninfected infants born to untreated mothers.

RESULTS

The infants ranged in age from 0 to 180 days. CSF PCR was positive in 27 of the 58 (46.5%) congenitally infected infants and was negative in each of the 103 infants without congenital toxoplasmosis. The frequency of positive CSF PCR varied according to whether infants had major clinical signs of the disease; PCR was positive in 70.9%, 53.3% and 50.9% of those with hydrocephalus, cerebral calcifications and/or eye disease, respectively. Of 6 infants who were negative for both IgM and IgA antibodies, 3 had a positive PCR in their CSF as the confirmatory test for diagnosis of congenital toxoplasmosis. IgM and IgA antibodies and CSF PCR, when combined, yielded a higher sensitivity for diagnosis of congenital toxoplasmosis when compared with the performance of each test alone.

CONCLUSIONS

Our findings reveal that in infants with clinical and serologic findings suggestive of congenital toxoplasmosis and born to untreated mothers, CSF PCR has the potential to increase the frequency of cases in which the diagnosis is confirmed.

Influence of iron status on risk of maternal or neonatal infection and on neonatal mortality with an emphasis on developing countries

Infection is a major cause of neonatal death in developing countries. This review investigates whether host iron status affects the risk of maternal and/or neonatal infection, potentially contributing to neonatal death, and summarizes the iron acquisition mechanisms described for pathogens causing stillbirth, preterm birth, and congenital infection. In vitro evidence shows that iron availability influences the severity and chronicity of infections that cause these negative outcomes of pregnancy. In vivo evidence is lacking, as relevant studies of maternal iron supplementation have not assessed the effect of iron status on the risk of maternal and/or neonatal infection. Reducing iron-deficiency anemia among women is beneficial and should improve the iron stores of babies; moreover, there is evidence that iron status in young children predicts the risk of malaria and, possibly, the risk of invasive bacterial diseases. Caution with maternal iron supplementation is indicated in iron-replete women who may be at high risk of exposure to infection, although distinguishing between iron-replete and iron-deficient women is currently difficult in developing countries, where a point-of-care test is needed. Further research is indicated to investigate the risk of infection relative to iron status in mothers and babies in order to avoid iron intervention strategies that may result in detrimental birth outcomes in some groups of women.