Real-time PCR as a prognostic tool for human congenital toxoplasmosis

Real-time PCR in the diagnosis of congenital toxoplasmosis

The diagnosis of congenital toxoplasmosis presents limitations and therefore new options are necessary. The analysis of amniotic fluid by real-time PCR has already proved effective for confirmation of fetal infection. However, its performance in other biological samples is not clear yet. The aim of this study is to better understand the role of real-time PCR in the blood of the mother and newborn as well as in the amniotic fluid and placenta in the diagnosis of congenital toxoplasmosis. This is a descriptive cohort study of pregnant women with toxoplasmosis followed up in Rio de Janeiro, Brazil. Real-time PCR was performed in samples of maternal blood, amniotic fluid, placenta, and blood of newborns. In addition, histopathological examination of placentas was performed, and data collected from babies were collected. 116 pregnant women were followed up and 298 samples were analyzed. One (0.9%) pregnant woman presented positive PCR in the blood, 3 (3.5%) in the amniotic fluid, 1 (2.3%) in the placenta and no newborn had positive PCR in the blood. Histopathological study was suggestive of toxoplasmosis infection in 24 (49%) placentas. Six (5.2%) newborns were diagnosed with congenital toxoplasmosis, and only cases with positive PCR in the amniotic fluid had correlation of the PCR result with the diagnosis of congenital infection. Both maternal and blood samples of newborns and placenta did not prove to be promising in the diagnosis of congenital toxoplasmosis. Further studies are needed to evaluate the real role of molecular diagnosis in other biological materials rather than the amniotic fluid.

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.

Congenital toxoplasmosis: Should we still care about screening?

Prenatal systematic screening for congenital toxoplasmosis has been performed in Austria and France since 1975 and neonatal screening for congenital toxoplasmosis has been part of the New England Newborn screening program since 1986. In this narrative review we review the data leading up to the systematic screening programs in Austria and France, highlighting the main finding of the European Union funded research in the 1990s and early 2000s. Different descriptive studies of the effect of pre- or postnatal treatment are discussed. Toxoplasma gondii has different genetic lineages with different pathogenicity in humans. This means that results in areas with a low pathogenic lineage cannot be extrapolated to an area with highly pathogenic lineages. The importance of meat as a source of infection is discussed in the light of an increased prevalence of T.gondii in organic livestock production .

Strain-specific pre-existing immunity: A key to understanding the role of chronic Toxoplasma infection in cognition and Alzheimer's diseases?

Toxoplasma exposure can elicit cellular and humoral immune responses. In the case of chronic Toxoplasma infection, these immune responses are long-lasting. Some studies suggest that pre-existing immunity from Toxoplasma infection can shape immune responses and resistance to other pathogens and brain insults later in life. Much evidence has been generated suggesting Toxoplasma infection may contribute to cognitive impairment in the elderly. However, there have also been studies that disagree with the conclusion. Toxoplasma has many strain types, with virulence being the most notable difference. There is also considerable variation in the outcomes following Toxoplasma exposure ranging from resolved to persistent infection. Therefore, the brain microenvironment, particularly cellular constituents, differs based on the infecting strain (virulent versus hypovirulent) and infection stage (resolved versus persistent). Such difference might play a critical role in determining the outcome of the host on subsequent challengings to the brain. The ability of Toxoplasma strains to set up distinct stages for neurodegenerative pathology through varying degrees of virulence provides unique experimental tools for characterizing these pathways.

Ocular Findings in Infants with Congenital Toxoplasmosis after a Toxoplasmosis Outbreak

PURPOSE

We investigated the prevalence of ocular abnormalities in infants vertically exposed to Toxoplasma gondii infection during an outbreak in Santa Maria City, Brazil.

DESIGN

Consecutive case series.

PARTICIPANTS

A total of 187 infants were included.

METHODS

The infants were recruited from January 2018 to November 2019. All mothers were screened for syphilis and human immunodeficiency virus before delivery. Toxoplasmosis infection was confirmed in all mothers and infants based on the presence of serum anti-T. gondii immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies. All infants underwent an ophthalmologic examination; ocular abnormalities were documented using a wide-field digital imaging system. Neonatal cranial sonography or head computed tomography was performed in 181 infants, and the cerebrospinal fluid (CSF) was screened for anti-T. gondii IgG and IgM antibodies in 159 infants. Peripheral blood samples from 9 infants and their mothers were analyzed for the presence of T. gondii DNA by real-time polymerase chain reaction.

MAIN OUTCOME MEASURES

Ocular abnormalities associated with congenital toxoplasmosis.

RESULTS

A total of 187 infants were examined. Twenty-nine infants (15.5%) had congenital toxoplasmosis, of whom 19 (10.2%) had ocular abnormalities, including retinochoroiditis in 29 of 38 eyes (76.3%), optic nerve abnormalities in 5 eyes (13.2%), microphthalmia in 1 eye (2.6%), and cataract in 2 eyes (5.3%). Bilateral retinal choroidal lesions were found in 10 of 19 infants (52.6%). Nine eyes of 6 infants had active lesions, with retinal choroidal cellular infiltrates at the first examination. Thirteen (7.2%) of 181 infants screened presented with cerebral calcifications. Eighty-three percent of the screened infants were positive for anti-T. gondii IgG and negative for IgM antibodies in the CSF. Congenital toxoplasmosis was higher in mothers infected during the third pregnancy trimester, and maternal treatment during pregnancy was not associated with a lower rate of congenital toxoplasmosis.

CONCLUSIONS

High prevalence rates of clinical manifestations were observed in infants with congenital toxoplasmosis after a waterborne toxoplasmosis outbreak, the largest yet described. Cerebral calcifications were higher in infants with ocular abnormalities, and maternal infection during the third pregnancy trimester was associated with a higher rate of congenital toxoplasmosis independent of maternal treatment.

PCR-based diagnosis is not always useful in the acute acquired toxoplasmosis in immunocompetent individuals

Toxoplasmosis is the most prevalent zoonosis in the world and is associated with a large spectrum of diseases. Acute acquired toxoplasmosis (AAT) is considered a benign and self-limiting disease but severe postnatal infections have been reported, particularly in South America. Laboratory diagnosis is based on the detection of anti-Toxoplasma gondii IgM, IgG, and presence of low IgG avidity. However, these assays present limitations, and therefore, PCR has been suggested as an alternative diagnostic tool. In this study, we performed real-time and nested PCR in DNA blood samples from 59 individuals with AAT lasting less than 80 days. None of the patients had parasitic DNA detected by PCR, even in the more severe cases or when blood was collected early after disease onset. These negative results indicate that the parasitemia kinetics needs investigation to determine the best time for blood sampling, especially in immunocompetent individuals. Thus, we emphasize that a negative PCR result does not exclude recent T. gondii infection, and serological criteria are still decisive for the laboratory diagnosis of AAT.

Use of polymerase chain reaction (PCR) in the diagnosis of congenital toxoplasmosis

Congenital toxoplasmosis (CT) is a parasitic disease that causes serious fetal and neonatal harm or death. In countries that do not have antenatal screening programs, the initiation of CT treatment relies on a postnatal diagnosis. Until recently, diagnosis was based on clinical signs and immunoglobulin seropositivity, which is fraught with difficulty. In these cases, diagnosis was often delayed or treatment, which carries risk, started empirically. We highlight the use of polymerase chain reaction to diagnose a case of congenital toxoplasmosis, allowing early treatment and justifying the treatment burden.

Advances in serological, imaging techniques and molecular diagnosis of Toxoplasma gondii infection

BACKGROUND

Toxoplasmosis is worldwide distributed zoonotic infection disease with medical importance in immunocompromised patients, pregnant women and congenitally infected newborns. Having basic information on the traditional and new developed methods is essential for general physicians and infectious disease specialists for choosing a suitable diagnostic approach for rapid and accurate diagnosis of the disease and, consequently, timely and effective treatment.

METHODS

We conducted English literature searches in PubMed from 1989 to 2016 using relevant keywords and summarized the recent advances in diagnosis of toxoplasmosis.

RESULTS

Enzyme-linked immunosorbent assay (ELISA) was most used method in past century. Recently advanced ELISA-based methods including chemiluminescence assays (CLIA), enzyme-linked fluorescence assay (ELFA), immunochromatographic test (ICT), serum IgG avidity test and immunosorbent agglutination assays (ISAGA) have shown high sensitivity and specificity. Recent studies using recombinant or chimeric antigens and multiepitope peptides method demonstrated very promising results to development of new strategies capable of discriminating recently acquired infections from chronic infection. Real-time PCR and loop-mediated isothermal amplification (LAMP) are two recently developed PCR-based methods with high sensitivity and specificity and could be useful to early diagnosis of infection. Computed tomography, magnetic resonance imaging, nuclear imaging and ultrasonography could be useful, although their results might be not specific alone.

CONCLUSION

This review provides a summary of recent developed methods and also attempts to improve their sensitivity for diagnosis of toxoplasmosis. Serology, molecular and imaging technologies each has their own advantages and limitations which can certainly achieve definitive diagnosis of toxoplasmosis by combining these diagnostic techniques.

Molecular diagnosis of symptomatic toxoplasmosis: a 9-year retrospective and prospective study in a referral laboratory in São Paulo, Brazil

Symptomatic forms of toxoplasmosis are a serious public health problem and occur in around 10–20% of the infected people. Aiming to improve the molecular diagnosis of symptomatic toxoplasmosis in Brazilian patients, this study evaluated the performance of real time PCR testing two primer sets (B1 and REP-529) in detecting Toxoplasma gondii DNA. The methodology was assayed in 807 clinical samples with known clinical diagnosis, ELISA, and conventional PCR results in a 9-year period. All samples were from patients with clinical suspicion of several features of toxoplasmosis. According to the minimum detection limit curve (in C_T), REP-529 had greater sensitivity to detect T. gondii DNA than B1. Both primer sets were retrospectively evaluated using 515 DNA from different clinical samples. The 122 patients without toxoplasmosis provided high specificity (REP-529, 99.2% and B1, 100%). From the 393 samples with positive ELISA, 146 had clinical diagnosis of toxoplasmosis and positive conventional PCR. REP-529 and B1 sensitivities were 95.9% and 83.6%, respectively. Comparison of REP-529 and B1 performances was further analyzed prospectively in 292 samples. Thus, from a total of 807 DNA analyzed, 217 (26.89%) had positive PCR with, at least one primer set and symptomatic toxoplasmosis confirmed by clinical diagnosis. REP-529 was positive in 97.23%, whereas B1 amplified only 78.80%. After comparing several samples in a Brazilian referral laboratory, this study concluded that REP-529 primer set had better performance than B1 one. These observations were based after using cases with defined clinical diagnosis, ELISA, and conventional PCR.

Association of Parasite Load Levels in Amniotic Fluid With Clinical Outcome in Congenital Toxoplasmosis

OBJECTIVE

To correlate neonatal and infant clinical outcome with parasite load in amniotic fluid (AF).

METHODS

We conducted a retrospective cohort study of 122 children whose mothers had toxoplasmosis during pregnancy. The children were monitored from birth to 12 months old. Stored AF samples were obtained at maternal diagnosis and tested by quantitative polymerase chain reaction. Gestational age at maternal infection, quantitative polymerase chain reaction results, neonatal anti-Toxoplasma gondii immunoglobulin (Ig) M, and clinical outcome at 12 months were correlated.

RESULTS

Maternal infection occurred in 18 of 122 (14.7%) and 104 of 122 (85.2%) women in the first and second trimesters, respectively. At birth, IgM was present in 107 of 122 (87.7%) neonates and 36 (29.5%) were symptomatic. Of these, half occurred in the first and the other half in the second trimester and 6 of 36 had severe infections (16.7% of symptomatic, 4.9% of total), all infected in the first trimester. Parasite load levels were highly variable (median 35 parasites/mL, range 2-30,473). Logistic regression correlated symptomatic infection with gestational age (odds ratio [OR] 0.47, CI 0.31-0.73) and parasite load (OR 2.04, CI 1.23-3.37), but not with positive IgM (OR 6.81, CI 0.86-53.9). Negative correlations were found between gestational age and parasite load (rs -0.780, CI -0.843 to -0.696), gestational age and symptoms (rs -0.664, CI -0.755 to -0.547), but not gestational age and IgM (rs -0.136, CI -0.311 to 0.048). Parasite load levels distributed by percentile showed that all symptomatic patients appeared from the 75th percentile and all severe infections from the 95th percentile. Load rankings showed doubled the OR for each 20 parasite/mL increment. Parasite load was associated with symptomatic infections (area under the curve 0.959, CI 0.908-0.987) as well as gestational age (area under the curve 0.918, CI 0.855-0.960) and both parameters combined (area under the curve 0.969, CI 0.920-0.992).

CONCLUSION

Parasite load in AF is associated with the clinical outcome in congenital toxoplasmosis, irrespective of gestational age at maternal infection.

Behavioral Abnormalities in a Mouse Model of Chronic Toxoplasmosis Are Associated with MAG1 Antibody Levels and Cyst Burden

There is marked variation in the human response to Toxoplasma gondii infection. Epidemiological studies indicate associations between strain virulence and severity of toxoplasmosis. Animal studies on the pathogenic effect of chronic infection focused on relatively avirulent strains (e.g. type II) because they can easily establish latent infections in mice, defined by the presence of bradyzoite-containing cysts. To provide insight into virulent strain-related severity of human toxoplasmosis, we established a chronic model of the virulent type I strain using outbred mice. We found that type I-exposed mice displayed variable outcomes ranging from aborted to severe infections. According to antibody profiles, we found that most of mice generated antibodies against T. gondii organism but varied greatly in the production of antibodies against matrix antigen MAG1. There was a strong correlation between MAG1 antibody level and brain cyst burden in chronically infected mice (r = 0.82, p = 0.0021). We found that mice with high MAG1 antibody level displayed lower weight, behavioral changes, altered levels of gene expression and immune activation. The most striking change in behavior we discovered was a blunted response to amphetamine-trigged locomotor activity. The extent of most changes was directly correlated with levels of MAG1 antibody. These changes were not found in mice with less cyst burden or mice that were acutely but not chronically infected. Our finding highlights the critical role of cyst burden in a range of disease severity during chronic infection, the predictive value of MAG1 antibody level to brain cyst burden and to changes in behavior or other pathology in chronically infected mice. Our finding may have important implications for understanding the heterogeneous effects of T. gondii infections in human.

Chronic infection with Toxoplasma gondii, a common neurotropic pathogen, affects approximately 1 billion people worldwide. There is marked variation in the human response to infection. Epidemiological studies indicate that virulent strains of T. gondii are associated with increased frequency and severity of human toxoplasmosis. However, animal studies on the pathogenic effect of chronic infection have focused on relatively avirulent strains because they can easily establish latent infections in mice. Employing a murine model of chronic infection with virulent strain, we found that mice displayed variable outcomes ranging from aborted to severe infections. Parasite burden, as measured serologically, was found to be the critical determinant of behavioral and pathogenic changes in chronically infected mice. This study demonstrated the predictive value of serologically determined parasite burden to the levels of chronic infection. Our finding highlights the critical role of parasite burden in a range of disease severity during chronic infection. Our finding may have important implications for understanding the heterogeneous effects of T. gondii infections in human.

A Brazilian report using serological and molecular diagnosis to monitoring acute ocular toxoplasmosis

Background

Toxoplasmosis was recently included as a neglected disease by the Center for Disease Control. Ocular toxoplasmosis is one clinical presentation of congenital or acquired infection. The laboratory diagnosis is being used worldwide to support the clinical diagnosis and imaging. The aim of this study was to evaluate the use of serology and molecular methods to monitor acute OT in immunocompetent patients during treatment.

Methods

Five immunocompetent patients were clinically diagnosed with acute OT. The clinical evaluation was performed by ophthalmologic examination using the Early Treatment Diabetic Retinopathy Study, best-corrected visual acuity, slit lamp biomicroscopy, fundoscopic examination with indirect binocular ophthalmoscopy color fundus photography, fluorescein angiography and spectral optical coherence tomography (OCT). Serology were performed by ELISA (IgA, IgM, IgG) and confirmed by ELFA (IgG, IgM). Molecular diagnoses were performed in peripheral blood by cPCR using the Toxoplasma gondiiB1 gene as the marker. Follow-up exams were performed on day +15 and day +45.

Results

Only five non-immunocompromised male patients completed the follow up and their data were used for analysis. The mean age was 41.2 ± 11.3 years (median: 35; range 31–54 years). All of them were positive for IgG antibodies but with different profiles for IgM and IgA, as well as PCR. For all patients the OCT exam showed active lesions with the inner retinal layers being abnormally hyper-reflective with full-thickness disorganization of the retinal reflective layers, which assumed a blurred reflective appearance and the retina was thickened.

Conclusions

The presence of IgA and IgM confirmed the acute infection and thus was in agreement with the clinical evaluation. Our results show the adopted treatment modified the serological profile of IgM antibodies and the PCR results, but not the IgG and IgA antibodies and that imaging is a good tool to follow-up patients.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1650-6) contains supplementary material, which is available to authorized users.

Genotyping of Toxoplasma gondii Directly from Human and Animal Biological Samples: From Partial Genotypes to a New Genotype

Genotyping of Toxoplasma gondii is traditionally performed using DNA obtained from tachyzoites after isolation by bioassay in mice. In this study, genotyping of T. gondii was performed by multiplex nested polymerase chain reaction restriction fragment length polymorphism (Mn-PCR-RFLP) in DNA obtained from the lungs of experimentally infected mice, the hearts of naturally infected free-range chickens, and human blood samples of newborns with congenital toxoplasmosis. The efficiency of Mn-PCR varied according to the marker. We obtained complete genotypes of all of the mice lung samples. In chickens, total or partial genotyping was performed on all of the 15 samples. Two complete genotypes were obtained, including one identified for the first time, and another previously described in different hosts including dogs, cats, and humans. In blood from infants, partial genotypes were obtained in 8 of the 12 samples. Mouse bioassay is the most efficient method to obtain DNA from T. gondii , but direct tissue genotyping enhances the likelihood of obtaining molecular information on T. gondii and is an effective tool as a complement to isolation in mice. In this study, we genotyped Toxoplasma gondii directly from human (blood samples of newborns with congenital toxoplasmosis) and free-range chickens (hearts) by Mn-PCR-RFLP. We present partial and complete genotypes and provide technical and scientific information about T. gondii genotyping methods.

Strain hypothesis of Toxoplasma gondii infection on the outcome of human diseases

The intracellular protozoan Toxoplasma gondii is an exceptionally successful food and waterborne parasite that infects approximately 1 billion people worldwide. Genotyping of T. gondii isolates from all continents revealed a complex population structure. Recent research supports the notion that T. gondii genotype may be associated with disease severity. Here, we (1) discuss molecular and serological approaches for designation of T. gondii strain type, (2) overview the literatures on the association of T. gondii strain type and the outcome of human disease and (3) explore possible mechanisms underlying these strain-specific pathology and severity of human toxoplasmosis. Although no final conclusions can be drawn, it is clear that virulent strains (e.g. strains containing type I or atypical alleles) are significantly more often associated with increased frequency and severity of human toxoplasmosis. The significance of highly virulent strains can cause severe diseases in immunocompetent patients and might implicated in brain disorders such as schizophrenia should led to reconsideration of toxoplasmosis. Further studies that combine parasite strain typing and human factor analysis (e.g. immune status and genetic background) are required for better understanding of human susceptibility or resistance to toxoplasmosis.

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.

Evaluation of a new protocol for retrospective diagnosis of congenital toxoplasmosis by use of Guthrie cards

The aim of this study was to assess the diagnostic value of IgM Western blotting (WB), IgA enzyme immunoassay (EIA), and DNA amplification by real-time PCR on Guthrie cards to retrospectively establish the diagnosis of congenital toxoplasmosis (CT). To this purpose, Guthrie cards were collected from 18 infants born to mothers with primary Toxoplasma gondii infection during pregnancy. Moreover, the analytical sensitivity of T. gondii PCR was assessed by testing mock dried blood specimens set up with several known DNA dilutions. IgM WB was demonstrated to be the most sensitive method. When the results of T. gondii DNA detection and specific IgM recovery were combined, retrospective CT diagnosis by using Guthrie cards was established in 3 out of 6 infected infants (sensitivity, 50%; 95% confidence interval, 26.8% to 73.2%). No positive PCR or serologic results were found in the group of 12 uninfected infants, demonstrating the excellent specificity of the three methods (95% confidence interval, 78.1% to 99.5%). The findings of the present study suggest that, in cases of missed diagnosis of CT at birth, analysis of Guthrie cards for children with compatible clinical findings after the perinatal period, in particular the combination of recovery of specific IgM antibodies and T. gondii DNA amplification, could be helpful. Nevertheless, since suboptimal conditions of storage of dried blood specimens can seriously affect sensitivity, negative results cannot rule out CT diagnosis. In contrast, because of the excellent specificity shown by IgM serologic testing and T. gondii DNA amplification on Guthrie cards, positive results obtained by either of the two methods should be considered diagnostic.