Effect of prenatal treatment on the risk of intracranial and ocular lesions in children with congenital toxoplasmosis

L Gras, RE Gilbert, AE Ades and DT Dunn

Centre for Paediatric Epidemiology and Biostatistics, Institute of Child Health, London, UK.

Abstract

Background Hydrocephalus, intracranial calcification and retinochoroiditis are the most common manifestations of tissue damage due to congenital toxoplasmosis, but the effect of prenatal treatment on these outcomes is unclear. We aimed to determine the effect of prenatal treatment for toxoplasmosis on the risk of intracranial and ocular lesions in congenitally infected children at 3 years of age.

Methods A cohort of mothers identified during pregnancy with toxoplasma infection and their 181 liveborn children with confirmed congenital toxoplasmosis was retrospectively analysed to determine the presence of intracranial and ocular lesions. As few women are not treated, we compared the effects of the treatment potency (pyrimethamine-sulfadiazine versus spiramycin or no treatment), and the timing of treatment, on the risks of intracranial lesions, time to detection of ocular lesions, and detection of any lesions (intracranial or ocular) by 3 years of age. Analyses took account of the gestation at maternal seroconversion.

Results There was no evidence for an effect of pyrimethamine-sulfadiazine on intracranial, ocular or any lesions by 3 years: odds ratio (OR) for any lesions 0.89 (95% CI : 0.41, 1.88). There was no evidence of an effect of delayed treatment on ocular lesions (hazard ratio = 0.69, 95% CI : 0.28, 1.68) or any lesions by 3 years of age (OR = 0.44, 95% CI : 0.16, 1.19).

Conclusions Our study failed to detect a beneficial effect of early or more potent anti toxoplasma treatment on the risks of intracranial or ocular lesions in children with congenital toxoplasmosis. However, larger, prospective studies, which determine the effect of prenatal treatment on long-term developmental outcomes are required to justify changes in clinical practice.

Keywords Congenital toxoplasmosis, prenatal treatment, intracranial calcification, retinochoroiditis

Accepted 24 May 2001

The aim of prenatal treatment for infection with Toxoplasma gondii is to prevent neurological or visual impairment in infected children either by preventing mother to child transmission of infection, or, once fetal infection has occurred, by limiting cell damage caused by the parasite.1,2,pp.173–75 In this report, we present results on the effect of prenatal treatment on lesions attributable to parasite-induced cell damage in children with confirmed congenital toxoplasmosis. The lesions most commonly associated with congenital toxoplasmosis are intracranial calcification or hydrocephalus, which are usually detected during infancy, and retinochoroiditis, which may appear at any age.2 Intracranial and/or ocular lesions were detected before school age in 33% (28/85) of congenitally infected children followed in three population-based cohort studies.3–5 Of the 28 with lesions, 3 (4%) had severe neurological impairment. Retinochoroidal lesions have been reported in 16% (14/85) children at 1–6 years old,3–5 of whom up to half may have permanent visual impairment, due to the size of the lesion and involvement of the macular area.3–6 Information is lacking on the risk of developmental impairment in children with intracranial or ocular lesions. However, many appear to develop normally6,7 and a small study comparing 17 congenitally infected children and their siblings raises the possibility that impairment may be worse in those with ocular than intracranial lesions (R Eaton, New England Neonatal Screening Program, personal communication).

The effect of prenatal treatment for toxoplasmosis on intracranial or ocular lesions is uncertain. In a study of 144 consecutive women referred to five fetal medicine centres, including 64 with infected children, Foulon et al.8 found a reduction in the risk of lesions at 1 year of age in children born to women given any prenatal treatment compared with those not treated (odds ratio [OR] = 0.3; 95% CI : 0.10, 0.86). However, this study and a case-control study of 103 infected children,9 found no evidence for an effect of the more potent regimen of pyrimethamine-sulfadiazine compared with spiramycin alone. Both studies endeavoured to account for the effect of gestation at maternal infection10 but failure to exclude women referred due to fetal abnormalities may have overestimated the risk of lesions in untreated women.

We investigated the effect of prenatal treatment on the risk of signs in a cohort of children with congenital toxoplasmosis born to infected women identified in Lyon, France. As few women received no treatment, we examined whether the risk of lesions was related to the potency of treatment used or to the interval between maternal seroconversion and the start of treatment.

Methods

Patients
The study is based on liveborn children with congenital toxoplasmosis of women who were prospectively identified with toxoplasma infection by the toxoplasma reference laboratory in Lyon, France, between 1987 and 1995. The study methods have been described elsewhere.10,11 Diagnosis of maternal infection was based on: (a) detection of seroconversion (change from negative to positive specific IgG antibodies); or (b) detection of IgM specific antibodies and, low IgG avidity (<35%), and/or rising specific IgG titre in women who were IgG positive at the first prenatal test. We excluded women referred for suspected fetal infection or abnormality based on scrutiny of referral letters or non-sequential dates for detection of maternal infection, fetal infection or fetal abnormalities. Spontaneous fetal losses or terminations were excluded from the analysis as fetal investigations for lesions (ultrasound or autopsy) were not routinely performed.

Prenatal treatment
After confirmation of infection, women were prescribed spiramycin (9 x 106 units/day) until delivery. If fetal diagnosis was positive, or maternal infection was acquired after 32 weeks, treatment consisted of pyrimethamine (50 mg/day) and sulfadiazine (3 g/day) alternating 3-weekly with spiramycin until delivery (subsequently referred to as pyrimethamine-sulfadiazine). Women with confirmed fetal infection and evidence of intracranial calcification or hydrocephalus on fetal ultrasound were offered termination.

Follow-up
Paediatric examinations were scheduled during the neonatal period, at 2, 5, 8, and 12 months of age, and annually thereafter, or until congenital infection had been excluded. At each visit, the child was examined for retinochoroidal lesions by direct ophthalmoscopy, usually after dilation of the iris, and a blood sample was taken for serology testing. Infants underwent cranial ultrasonography or radiography or both. The dates at which intracranial calcification, hydrocephalus or the first ocular lesion was first detected or the date of the last negative examination was recorded for analysis. We did not analyse the effect of treatment on recurrence of lesions or on the size or site of lesions.

Congenital toxoplasmosis was diagnosed if there was persistence of specific IgG antibodies beyond 12 months of age. Absence of congenital toxoplasmosis was based on a decline in IgG specific antibody beyond detectable levels after discontinuation of treatment. All mother-child pairs in which infection status was unknown were excluded from the analysis.

Postnatal treatment
Neonates with suspected infection were prescribed pyrimethamine (3 mg/kg/3 days) and sulfadiazine (75 mg/kg/day) for 3 weeks, followed by spiramycin (0.375 x 106 units/kg/day) for 2–5 weeks, followed by pyrimethamine (6 mg/kg/10 days) and sulphadoxine (125 mg/kg/10 days) with folinic acid for at least 12 months. All other infants received spiramycin alone pending further evidence of congenital infection status.

Analysis
We investigated the effect of prenatal treatment in two ways. First, we compared the risk of lesions in children born to women treated with spiramycin with those treated with pyrimethamine-sulfadiazine or not treated. We hypothesized that pyrimethamine-sulfadiazine would be more effective in reducing the risk of lesions because it reaches higher levels in fetal blood and, in contrast to spiramycin, is able to penetrate the blood brain barrier.12 We conducted separate analyses of the effect of treatment on the risks of intracranial and ocular lesions and on any lesions (intracranial or ocular) detected by 3 years of age (follow-up was complete for 95% of the person years of follow-up to 3 years of age). Second, we compared the risk of intracranial, ocular or any lesions in children born to women prescribed any treatment within 4 weeks of estimated seroconversion with those treated 4 or more weeks after seroconversion or not treated.

We used a statistical model, previously described10,11 to take account of the effect of gestation at seroconversion and the interval between seroconversion and treatment (defined as treatment delay) on the risk of lesions. For women who were IgG positive at the first prenatal test, we assumed that seroconversion occurred between conception and the first positive test.

In the analyses of the risk of intracranial lesions and of any lesion by age 3, we assumed that the effects of treatment and gestational age at seroconversion were additive on a logistic scale. We used a Weibull model to analyse the effect of treatment on the time to first detection of the first ocular lesion and assumed that the hazard was proportional according to treatment categories and gestation at seroconversion. Kaplan-Meier estimates were used to determine the proportion of children without ocular signs according to year of age. The association between the presence of ocular and intracranial lesions was assessed using Fisher's exact test.

Results

Mother to child transmission of infection occurred in 194 of the 704 infected pregnancies with complete data (Figure 1Go, preceding paper11), of which 181 resulted in a live birth. Of the 13 non-live births, 8 fetuses were terminated after 22 weeks, 5 due to hydrocephalus or ventricular dilatation on ultrasound scan: one also had retinochoroidal lesions detected at autopsy. Five fetuses spontaneously aborted or were stillborn, one immediately after cordocentesis at 30 weeks gestation. All analyses presented are based on the 181 congenitally infected liveborn children.



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Figure 1 Time till detection of first retinochoroidal lesion in 181 children with congenital toxoplasmosis

Vertical lines represent 95% confidence intervals.

 
Prenatal treatment consisted of pyrimethamine-sulfadiazine in 70/181 women (39%), spiramycin alone in 89/181 women (49%), and 22/181 (12%) were not treated. The estimated median interval between seroconversion and the start of treatment with pyrimethamine-sulfadiazine was 7 weeks (interquartile range [IQR] 4–10 weeks), and for spiramycin, 4 weeks (IQR 2–7 weeks).

All 181 infected children were treated postnatally. In 177 children, treatment was started within 2 months of birth. All but four children were prescribed pyrimethamine-sulfadiazine and/or pyrimethamine-sulphadoxine. The median age when treatment was stopped was 22 months (IQR 17 months– 28 months).

Intracranial and ocular lesions
Hydrocephalus was detected after birth in two children: one also had intracranial calcification; the other died at 8 days of age with hepatitis and disseminated intravascular coagulation after delivery at 34 weeks gestation, following maternal seroconversion between 15 and 22 weeks and prenatal treatment with spiramycin. Intracranial calcification was reported in a total of 17/181 (9%) children. None of the lesions in liveborn children were detected prenatally. In 14 children, the first skull X-ray or cranial ultrasound after birth revealed intracranial calcifications. In one child, intracranial calcification was suspected at birth but not confirmed until the next radiological examination at 3 years old. Two children had normal skull X-rays and ultrasound examinations after birth but intracranial calcification was detected on CT scan when they were re-examined, due to epilepsy, at 2 and 3 years of age.

Retinochoroidal lesions were detected in 37 children after a median follow-up of 6 years 5 months. Figure 1Go shows that 7/181 (4%) children had lesions detected during the first month of life, 16 (9%) by 6 months, 19 (11%) by 12 months, 29 (16%) by 3 years, 32 (19%) by 5 years and 36 (23%) by 7 years. Overall, 21/181 children were not completely followed up to 3 years. Follow-up was complete for 95% (516/543) of the total person years up to age 3.

Hydrocephalus, intracranial calcification, and/or ocular lesions were detected by 3 years of age in 38/181 (21%) liveborn children. Ocular lesions were more common in children with intracranial calcification (9/17, 53%) than in children without intracranial calcification (21/164, 13%; P = 0.0015).

Effect of type of treatment
There was no evidence that the risk of intracranial lesions (hydrocephalus or intracranial calcification) was reduced in children born to mothers prescribed pyrimethamine-sulfadiazine compared with those prescribed spiramycin alone (adjusted OR = 0.90, 95% CI : 0.29, 2.64) and similarly for untreated mothers compared with those prescribed spiramycin (adjusted OR = 1.04, 95% CI : 0.05, 8.13) (Table 1Go). Second, there was no evidence that women prescribed pyrimethamine-sulfadiazine were less likely to have children who developed ocular lesions at any age compared with women prescribed spiramycin alone (adjusted hazard ratio = 1.13, 95% CI : 0.56, 2.47). We estimated that if the mother seroconverted at 24 weeks gestation and gave birth to an infected child, the risk of ocular lesions by age 3 years was 15.9% given spiramycin alone, and 17.7% given pyrimethamine-sulfadiazine treatment prenatally: estimated difference—1.8%, (95% CI : -12.7, 8.7%). Finally, we found no evidence that the type of prenatal treatment had an effect on the risk of any lesions by age 3 years (adjusted OR associated with pyrimethamine-sulfadiazine compared with spiramycin = 0.93, 95% CI : 0.42, 2.04).


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Table 1 Effect of prenatal treatment on intracranial and ocular lesions in children with congenital toxoplasmosis
 
Effect of treatment delay on clinical signs
The distribution of mother-child pairs, according to type of lesions, estimated treatment delay and gestation at seroconversion is shown in Figure 2Go. An estimated 40% (72/181) of women were treated within 4 weeks after seroconversion, 34% (58/181) were treated between 4 and 8 weeks, and 16% (29/181) after 8 weeks or more. Of the 22 women who were not treated, postnatal treatment was started within the first three weeks of life in 19 children, after 11/2 months in two and after 3 months in one.



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Figure 2 Estimated gestational age at seroconversion and treatment delay according to type of lesion

Dark grey dots = both ocular and intracranial lesions, black dots = ocular lesions by age 3, light grey dots = intracranial lesions and transparent dots = no lesions detected. Treatment delay is plotted against gestation at seroconversion. We assumed that for untreated women, treatment of the child started at delivery. Both measures are based on the estimated date for seroconversion, which was a weighted mean of all possible dates for each woman (weighted by the probability of seroconversion).

 
Mothers who gave birth to children with intracranial lesions were significantly more likely to have seroconverted earlier in pregnancy (OR per week of gestation = 0.90, 95% CI : 0.84, 0.97), whereas we did not detect a significant effect of gestation at seroconversion on the risk of ocular lesions (OR = 0.97, 95% CI : 0.93, 1.02).

There was no evidence that delayed treatment had a significant effect on the time to detection of ocular lesions (adjusted hazard ratio for treatment after 4 weeks/no treatment compared with treatment within 4 weeks of seroconversion = 0.69, 95% CI : 0.28, 1.68) or on the risk of any lesions by 3 years of age (adjusted OR = 0.44, 95% CI : 0.16, 1.19).

As treatment may have an effect on mother to child transmission, we determined the overall effect of early (within 4 weeks of seroconversion) compared with delayed or no treatment on the risk of lesions by 3 years of age in infected and uninfected children born to seroconverting women (see preceding paper11). The adjusted OR for any lesion at 3 years associated with delayed or no treatment compared with early treatment was 0.63 (95% CI : 0.24, 1.58).

Discussion

We have analysed the largest reported cohort of children with congenital toxoplasmosis, taking care to minimize selection bias due to women with affected fetuses, and taking account of the effect of gestation at maternal seroconversion on the risk of lesions.10 We found no evidence that prenatal treatment with pyrimethamine-sulfadiazine compared with spiramycin reduced the risk of intracranial or ocular lesions although the 95% CI included both beneficial and harmful effects. There was also no evidence that spiramycin compared with no treatment reduced the risk of intracranial or ocular lesions but due to the small sample size of the untreated group, the power to detect a significant difference between spiramycin and untreated women is low. We also found no evidence that delayed treatment (after 4 or more weeks after seroconversion) or no treatment, reduced the risk of clinical signs by 3 years of age, compared with early treatment (within 4 weeks of seroconversion).

Unexpectedly, the risk of intracranial lesions was significantly reduced in children born to women treated after a delay or not treated at all. Children born to women treated after 4 or more weeks or not treated had a significantly lower risk of intracranial lesions, than for women treated within 4 weeks of seroconversion (adjusted OR = 0.08, 95% CI : 0.01, 0.45). This result may have occurred by chance and is not confirmed by preliminary findings from a larger, prospective European Multicentre Study on Congenital Toxoplasmosis (EMSCOT, unpublished data, R Gilbert). We also considered alternative explanations. First, abnormal fetal ultrasound findings may have led to prompt treatment. After re-checking all patient files, we found no cases of suspected fetal ultrasound abnormalities prior to diagnosis of maternal infection. Second, we investigated whether maternal symptoms of infection could be associated with early treatment and an increased risk of clinical signs but found no evidence of an association: 5% (11/181) of women reported symptoms, of whom one gave birth to a child with signs. A third possible explanation for the reduced risk of intracranial lesions with delayed or no treatment is that early treatment with pyrimethamine-sulfadiazine suppresses the bone marrow2,p.227 and compromises the maternal and/or fetal immune responses that limit parasite-induced cell damage.13–15 Our results need to be investigated in more powerful studies that can analyse the effect of early versus delayed treatment according to treatment type.

The lack of evidence for an effect of the more potent regimen of pyrimethamine-sulfadiazine compared with spiramycin alone or no treatment, may be due to treatment after encystment of the parasite has occurred. Once T. gondii tachyzoites have crossed the placenta, transformation to the bradyzoite form can occur within days,16 probably due to stresses caused by the humoral and cell mediated immune responses.17 Neither spiramycin nor pyrimethamine-sulfadiazine is effective against the encysted, bradyzoite form of the parasite, although experimental studies show that both are effective against the free tachyzoite form.12 As treatment is always given some time, often weeks, after maternal antibodies develop, it may be given after encystment of the parasite. Due to limitations of sample size and the fact that few women receive pyrimethamine/sulfadiazine immediately after detection of maternal seroconversion, we could not investigate the effects of timing of different types or dosages of treatment.

We found a significant effect of gestation at maternal seroconversion on the risk of intracranial lesions, but a less marked effect on the risk of ocular lesions. These findings may reflect differing immune responses at the two sites resulting in different patterns of lesion development.17,18

Conclusions

Our study failed to detect a beneficial effect of prenatal treatment on the risk of clinical signs in infected children. Although ours is the largest study to date to address this question, the confidence intervals for the effects of different types of treatment are wide. Consequently, we cannot exclude potentially beneficial or harmful effects. The significant finding of a beneficial effect of delayed treatment on intracranial lesions may be due to chance and requires confirmation by further studies. A further concern is the lack of information on the association between intracranial lesions and subsequent developmental impairment. Larger, prospective studies, which determine the effect of prenatal treatment on long-term developmental outcomes are therefore required to justify changes in clinical practice.

Acknowledgments

The study was funded by The Wellcome Trust and by the European Commission BIOMED programme (BMH4-CT98–3927). We thank the staff of Laboratoire de Parasitologie et de Pathologie Exotique, Hôpital de la Croix Rousse, Lyon, for help with data collection and Eskild Petersen for helpful comments on drafts of the report and facilitating the collaboration. We thank Martine Wallon and Francois Peyron for providing the data and for contributing to the design, execution and interpretation of the study. The conclusions in this paper do not reflect the opinions of the clinicians in the department which provided the data.

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