Congenital toxoplasmosis: the importance of the western blot method to avoid unnecessary therapy in potentially infected newborns

Diagnostic methods and protocols used in investigating Toxoplasma gondii in humans: A review

Toxoplasmosis, a zoonotic disease, is a parasitic infection caused by a coccidian protozoan Toxoplasma gondii. In immunocompetent people, the infection is asymptomatic, while it can produce serious signs in immunocompromised people and in developing fetuses. Accurate diagnosis is dependent, mainly, on the clinical features. However, in immunocompromised patients, the diagnosis is very difficult and may lead to misdiagnosis and improper treatment. Today, molecular diagnosis and serotyping are widely used for the diagnosis of T. gondii in many countries. The aim of the present short review is to highlight the current diagnostic methods and protocols that are used for the diagnosis of T. gondii in humans.

Performance of Zika Assays in the Context of Toxoplasma gondii, Parvovirus B19, Rubella Virus, and Cytomegalovirus (TORCH) Diagnostic Assays

Infections during pregnancy that may cause congenital abnormalities have been recognized for decades, but their diagnosis is challenging. This was again illustrated with the emergence of Zika virus (ZIKV), highlighting the inherent difficulties in estimating the extent of pre- and postnatal ZIKV complications because of the difficulties in establishing definitive diagnoses. We reviewed the epidemiology, infection kinetics, and diagnostic methods used for Toxoplasma gondii, parvovirus B19, rubella virus, and cytomegalovirus (TORCH) infections and compared the results with current knowledge of ZIKV diagnostic assays to provide a basis for the inclusion of ZIKV in the TORCH complex evaluations. Similarities between TORCH pathogens and ZIKV support inclusion of ZIKV as an emerging TORCH infection. Our review evaluates the diagnostic performance of various TORCH diagnostic assays for maternal screening, fetal screening, and neonatal screening. We show that the sensitivity, specificity, and positive and negative predictive value of TORCH complex pathogens are widely variable, stressing the importance of confirmatory testing and the need for novel techniques for earlier and accurate diagnosis of maternal and congenital infections. In this context it is also important to acknowledge different needs and access to care for different geographic and resource settings.

Contribution of a Comparative Western Blot Method to Early Postnatal Diagnosis of Congenital Syphilis

Serology has a pivotal role in the diagnosis of congenital syphilis (CS), but problems arise because of the passive transfer of IgG antibodies across the placenta. The aim of this study was to assess the diagnostic value of a comparative Western blot (WB) method finalized to match the IgG immunological profiles of mothers and their own babies at birth in order to differentiate between passively transmitted maternal antibodies and antibodies synthesized by the infants against Treponema pallidum Thirty infants born to mothers with unknown or inadequate treatment for syphilis were entered in a retrospective study, conducted at St. Orsola-Malpighi Hospital, Bologna, Italy. All of the infants underwent clinical, instrumental, and laboratory examinations, including IgM WB testing. For the retrospective study, an IgG WB assay was performed by blotting T. pallidum antigens onto nitrocellulose sheets and incubating the strips with serum specimens from mother-child pairs. CS was diagnosed in 11 out of the 30 enrolled infants; 9/11 cases received the definitive diagnosis within the first week of life, whereas the remaining two were diagnosed later because of increasing serological test titers. The use of the comparative IgG WB testing performed with serum samples from mother-child pairs allowed a correct CS diagnosis in 10/11 cases. The CS diagnosis was improved by a strategy combining comparative IgG WB results with IgM WB results, leading to a sensitivity of 100%. The comparative IgG WB test is thus a welcome addition to the conventional laboratory methods used for CS diagnosis, allowing identification and adequate treatment of infected infants and avoiding unnecessary therapy of uninfected newborns.

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.

Toxoplasmosis in pregnancy in an area with low seroprevalence: is prenatal screening still worthwhile?

BACKGROUND

The effectiveness of Toxoplasma gondii (Tg) screening during pregnancy in areas with a low prevalence of the infection is debated. We investigate the Tg serological status, the rate of primary infection in a cohort of pregnant women and the rate of congenital toxoplasmosis among their infants during a 3-year period in an urban area with low Tg prevalence.

METHODS

Demographic and Tg serological data for all pregnant women delivering from January 2009 to December 2011 were collected. All pregnant women with primary Tg infection during pregnancy and their infants were included in the study.

RESULTS

In early pregnancy, 10,347 women underwent prenatal screening and 2308 (22.3%) had anti-Tg. The seroprevalence among non-native women was significantly higher than that among native women [32.8% vs. 19.1%, relative risk: 1.71, P < 0.001]. The incidence rate of primary Tg infection during pregnancy was 0.77%. Immigrant women were more likely to be infected during pregnancy than Italian women (relative risk: 4.88, P < 0.001). Tg infection was more frequent in women coming from Africa, Asia, Eastern Europe and South America. The CT incidence rate was 0.06%. All congenitally infected infants were born to immigrant mothers.

CONCLUSIONS

Tg infection during pregnancy and congenital disease are more frequent in non-native mothers and their infants. Measures to prevent Tg exposition must be carefully explained to pregnant women, with a focus on specific habits in non-native women. Prenatal screening is still effective to select women for prenatal therapy aiming to decrease vertical transmission and to identify foetuses/newborns with congenital disease that could benefit from pre/postnatal antiparasitic therapy.

Investigation and management of Toxoplasma gondii infection in pregnancy and infancy: a prospective study

AIM

Toxoplasma gondii infection during pregnancy poses a serious risk to the fetus, therefore timely and accurate diagnosis is essential. The aim of this study was to estimate the frequency of congenital infection via evaluating mother's immunological status and the possibility to improving the diagnostic and therapeutic approaches.

METHODS

Eighty five mothers with Toxoplasma seroconversion and their offspring were enrolled (among them, 2 spontaneous abortions were documented in the first trimester). Prenatal PCR diagnosis was carried out on 50 patients (60%), with 7 positive cases (14%). Morphological ultrasound scanning revealed anomalies in one fetus. Long-term follow-up included general physical examinations, serological status tested using Western blot, neuro-radiological, ophthalmologic and neurologic examinations, psychological and developmental tests, visual evoked potential tests and audiology tests, as well as anti-Toxoplasma treatment regimes.

RESULTS

Fourteen (17%) of the infants were infected at one-year serological follow-up. Chi-square for linear trend of vertical transmission from the first to the third trimester was significant (P=0.009). Western blot analysis showed IgM and IgA in half of the infected infants. In 69 uninfected infants, anti-Toxoplasma IgG immunoblot analysis excluded infection within the 3 months in 18 infants (26%) and in the others within 6 months of life. The most relevant instrumental findings are described.

CONCLUSION

Western blot analysis may help to evaluate infection within the 6 months of life. The accuracy of ultrasound imaging to determine the brain damage in the fetus and newborns is doubtful, and should be combined with MR imaging. Multistep approaches can improve the timing of postnatal follow-up.