What is known about the prevention of congenital toxoplasmosis?

Toxoplasmosis: Overview from a One Health perspective

Toxoplasmosis is paradigmatic of the One Health approach, as the causative parasite Toxoplasma gondii infects virtually all warm-blooded animals, including humans. This makes T. gondii one of the most successful parasites on earth, infecting up to a third of the global human population. Moreover, the T. gondii disease burden has been ranked among the highest of all parasitic diseases. To reduce the disease burden of toxoplasmosis in humans, interventions are needed in the animal reservoirs, necessitating close collaboration between both the human and veterinary medical sectors. In the present special issue of FAWPAR, several of the most pertinent topics related to the impact and control of toxoplasmosis are addressed by leading experts in the field. This collection of papers highlights state-of-the-art knowledge, gaps in knowledge and future perspectives, as well as the benefits of current and proposed future activities to tackle toxoplasmosis within the One Health context.

Towards Universal Screening for Toxoplasmosis: Rapid, Cost-Effective, and Simultaneous Detection of Anti-Toxoplasma IgG, IgM, and IgA Antibodies by Use of Very Small Serum Volumes

Rapid, cost-effective, and early determination of the serological status of potentially infected individuals, particularly pregnant women, can be critical in preventing life-threatening infections and subsequent fetal congenital abnormalities. An article in this issue of the Journal of Clinical Microbiology (X. Li, C. Pomares, G. Gonfrier, B. Koh, S. Zhu, M. Gong, J. G. Montoya, and H. Dai, J Clin Microbiol 54:1726-1733, 2016, http://dx.doi.org/10.1128/JCM.03371-15) describes an innovative multiplexed immunoassay that offers a path toward universal screening.

Screening cytomegalovirus, rubella and toxoplasma infections in pregnant women with unknown pre-pregnancy serological status

PURPOSE

To determine the prevalence of acute cytomegalovirus (CMV), rubella and T. gondii infections among pregnant women who had no serological status tested for these microorganisms prior to pregnancy in a metropolitan area.

METHODS

A cross-sectional study was undertaken between January 2009 and January 2013 in 1,258 women presenting for their first antenatal visit (between 6 and 11 weeks of gestation). All women were tested for IgG and IgM antibodies. Subsequently, avidity test was utilized for inconclusive results. They were followed until delivery and all newborns were examined by a pediatrician.

RESULTS

Presence of IgM antibody positivity alone was not detected in any women. Avidity test excluded primary infection in 15 out of 16 (93.7 %) women who were positive for both IgG and IgM antibodies. Amniocentesis was performed in one case with borderline IgG avidity for T. gondii. No primary infections were detected in any newborn for the infections screened. The prevalences of IgG antibodies were 95 % for rubella, 84.1 % for CMV and 23.1 % for T. gondii.

CONCLUSIONS

Assessment of IgG and IgM antibodies followed by IgG avidity testing for inconclusive results may be an acceptable approach in pregnant women with unknown serological status prior to pregnancy. Utilization of IgG avidity as a supplemental test prevented unnecessary intervention in IgG and IgM antibodies positive patients. No primary infection was detected for CMV, rubella and T. gondii infections in the urban population screened.

Effectiveness of health education on Toxoplasma-related knowledge, behaviour, and risk of seroconversion in pregnancy

We conducted a bibliographic literature search using MEDLINE to review the effectiveness of health education on Toxoplasma-related knowledge, behaviour, and risk of seroconversion in pregnant women. We pre-selected studies that used comparative study designs (randomized clinical trial, quasi-experimental design or historical control), that were conducted among pregnant women, and which employed specific, Toxoplasma-related outcome measures: knowledge, behaviour, or Toxoplasma infection rate. Four studies met the inclusion criteria. All had serious methodological flaws. A Belgian study reported a significant decrease in the incidence of Toxoplasma seroconversion after the introduction of intensive counselling for pregnant women about toxoplasmosis. In Poland, a significant increase in knowledge was observed after a multi-pronged, public health educational program was launched. In Canada, an increase in knowledge and prevention behaviours was reported in the intervention group receiving counselling by trained facilitators compared with the control group. In France, no significant changes in risk behaviour were observed following a physician-delivered intervention. This review highlights the weakness of the literature in the area and the lack of studies measuring actual seroconversion. There is suggestive evidence that health education approaches may help reduce risk of congenital toxoplasmosis but this problem requires further study using more rigorous research design and methodology.

Congenital toxoplasmosis: priorities for further health promotion action

Toxoplasmosis is a disease of considerable public health impact. As the transmission, occurrence and phenotype of this disease are influenced in a complex way by host genetics, immunity, behaviour and by the agent characteristics, prevention will not be simple. This article aimed to review studies defining seroprevalence of and characteristic sociodemographic, biological and lifestyle risk factors for Toxoplasma gondii infection in pregnant women, to evaluate screening and educational programmes, and to assemble recommendations for combating toxoplasmosis in populations at risk. Electronic databases were searched, using a specific search strategy, from 1975 to 2007. There is a high prevalence of T. gondii antibodies in pregnant women worldwide, with some geographic discrepancies attributed to climatic conditions, local food customs, hygiene, lifestyle and cultural differences. The main risk factors for toxoplasmosis in pregnant women are unsanitary feeding habits, poor immune system, contact with cats, contact with soil, pregnancy, number of births, older age, race, travelling outside the country, drinking beverages prepared with unboiled water, consumption of municipal or uncontrolled (well/spring) water and T. gondii strain virulence. Knowledge of these risk factors helps to identify priorities for further epidemiological work and defines effective preventive measures along five main themes of action: information and health education; screening of pregnant women and infants; limiting harm from risk behaviour; treatment of cases found to be at risk; and vaccination.

Biases in observational studies of the effect of prenatal treatment for congenital toxoplasmosis

The paper reviews methodological difficulties that arise when using observational studies to evaluate the effect of prenatal screening and treatment. The principle of each difficulty is described and then illustrated by a clinical example of toxoplasmosis in pregnancy and its consequences. Methods to deal with these difficulties are described. Given the limitations of existing observational studies and lack of randomised controlled trials, a systematic review of cohort studies offers the best approach for exploring potential biases.

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

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.

Effect of prenatal treatment on mother to child transmission of Toxoplasma gondii: retrospective cohort study of 554 mother-child pairs in Lyon, France

BACKGROUND

The aim of prenatal serological screening for toxoplasmosis is to identify and treat maternal infection as soon as possible in order to prevent transmission of the parasite to the fetus. However, despite widespread provision of prenatal toxoplasma screening across Europe, the effectiveness of prenatal treatment is uncertain. The study aimed to determine the effect of the timing and type of prenatal treatment on mother to child transmission of Toxoplasma gondii.

METHOD

A cohort of 554 infected pregnant women were identified in Lyon, France between 1987 and 1995 and their children were followed to determine congenital infection status. We determined the effect of prenatal treatment on transmission by examining the effect of the delay between maternal seroconversion and start of treatment. We also compared the effect of the type of treatment and no treatment on the risk of mother to child transmission. Analyses were adjusted for gestation at maternal seroconversion.

RESULTS

Compared to treatment within 4 weeks from seroconversion, the adjusted odds ratios (OR) for mother to child transmission after a treatment delay of 4-7 weeks was 1.29 (95% CI : 0.61, 2.73) and after more than 8 weeks, 1.44 (95% CI : 0.60, 3.31). The adjusted OR associated with spiramycin alone compared with pyrimethamine-sulfadiazine treatment was 0.91 (95% CI : 0.45, 1.84) and the OR for no treatment compared with pyrimethamine-sulfadiazine treatment was 1.06 (95% CI : 0.37, 3.03).

CONCLUSIONS

The authors hypothesize that the absence of an effect of prenatal treatment is due to transmission before the start of treatment.

Congenital toxoplasmosis: a review

Toxoplasmosis is caused by infection with the protozoan parasite Toxoplasma gondii. In the United States, approximately 85% of women of childbearing age are susceptible to acute infection with T. gondii. Acute infections in pregnant women may cause serious health problems when the organism is transmitted to the fetus (congenital toxoplasmosis), including mental retardation, seizures, blindness, and death. An estimated 400 to 4000 cases of congenital toxoplasmosis occur in the U.S. each year. Manifestations of congenital toxoplasmosis may not become apparent until the second or third decade of life. Serologic tests are used to diagnose acute infection in pregnant women, but false-positive tests occur frequently, therefore, serologic diagnosis must be confirmed at a reference laboratory before treatment with potentially toxic drugs should be considered. Much of congenital toxoplasmosis can be prevented by educating women of childbearing age and pregnant women to avoid eating raw or undercooked meat, to avoid cross-contamination of other foods with raw or undercooked meat, and to use proper cat-litter and soil-related hygiene.

Evaluation of solid-phase chemiluminescent enzyme immunoassay, enzyme-linked immunosorbent assay, and latex agglutination tests for screening toxoplasma IgG in samples obtained from cats and pigs

Serum samples from cats and pigs were analyzed by the solid-phase chemiluminescent enzyme immunoassay (SPCEI), enzyme-linked immunosorbent assay (ELISA), and indirect latex agglutination (ILA) methods. The SPCEI and ILA methods accurately analyzed Toxoplasma IgG (T-IgG) in both clinical and spiked samples from pigs and cats. The ELISA method accurately analyzed T-IgG in spiked samples from cats and pigs or clinical samples from pigs, but it did not accurately analyze T-IgG in clinical samples from cats. The antibody used in the ELISA kit did not cross-react with cat T-IgG. The SPCEI method that uses a stand-alone automated analyzer provided quantitative analysis, whereas the ELISA and ILA methods provided qualitative or, at best, semiquantitative analysis of T-IgG. The SPCEI and ELISA methods were rapid (60-90 minutes for 30 samples), whereas the ILA method required 13-15 hours for 30 samples. Although the three methods accurately distinguished positive from negative samples, the ILA method yielded many weakly positive results that were not confirmed by either the ELISA or SPCEI method. Thus, the indirect agglutination tests may give nonspecific responses at lower T-IgG concentrations.

Treatments for toxoplasmosis in pregnancy

BACKGROUND

Toxoplasmosis is a widespread parasitic disease and usually causes no symptoms. However, infection of pregnant women may cause congenital infection, resulting potentially in mental retardation and blindness in the infant.

OBJECTIVES

The objective of this review was to assess whether or not treating toxoplasmosis in pregnancy reduces the risk of congenital toxoplasma infection and improves infant outcomes.

SEARCH STRATEGY

The Cochrane Pregnancy and Childbirth Group trials register was searched. An electronic search was performed using the key words 'congenital and toxoplasmosis' on the following databases: MEDLINE (1966-07/1997), Embase (1993-07/1997), Pascal (French) (1990-1997), Biological Abstracts (1993-1995) and the Cochrane Controlled Trials Register. There was also contact with experts in the field, including those in the European Research Network on Congenital Toxoplasmosis.

SELECTION CRITERIA

Randomised controlled trials of antibiotic treatment versus no treatment of pregnant women with proven or likely acute Toxoplasma infection, with outcomes in the children reported. We also inspected relevant reports of less robust experimental studies in which there were (non randomly allocated) control groups, although it was not planned to include such data in the primary analysis.

DATA COLLECTION AND ANALYSIS

Reports of possibly eligible studies were scrutinised by two investigators.

MAIN RESULTS

Out of the 2591 papers identified, none met the inclusion criteria.

REVIEWER'S CONCLUSIONS

Despite the large number of studies performed over the last three decades we still do not know whether antenatal treatment in women with presumed toxoplasmosis reduces the congenital transmission of Toxoplasma gondii. Screening is expensive, so we need to evaluate the effects of treatment, and the impact of screening programmes. In countries where screening or treatment is not routine, these technologies should not be introduced outside the context of a carefully controlled trial.

Control of congenital infection with Toxoplasma gondii by neonatal screening based on detection of specific immunoglobulin M antibodies eluted from phenylketonuria filter-paper blood-spot samples

Two ongoing neonatal screening programmes for congenital infection with Toxoplasma gondii are presented. The New England Newborn Screening Programme has included congenital toxoplasmosis since 1986. The test is based on detection of Toxoplasma-specific immunoglobulin M (IgM) antibodies eluted from the phenylketonuria (PKU) card. The seroprevalence of Toxoplasma IgG antibodies is at present about 13% and the birth prevalence of congenital toxoplasmosis approximately 1 per 10000 liveborn children. The Danish national neonatal screening programme was expanded to include congenital toxoplasmosis from 1 January 1999. The test is also based on detection of Toxoplasma-specific IgM antibodies eluted from PKU cards. The seroprevalence of Toxoplasma IgG antibodies in pregnant women is around 25% and the birth prevalence about 1 per 3000 liveborn children. The birth prevalence of congenital Toxoplasma infection is within the range of other congenital disorders included in different screening programmes. Neonatal screening is feasible in areas with a low risk of congenital infection where prenatal screening will not be applicable.

Congenital toxoplasmosis: systematic review of evidence of efficacy of treatment in pregnancy

OBJECTIVE

To summarise the evidence that treating toxoplasmosis in pregnancy reduces the risk of congenital toxoplasma infection and improves infant outcomes.

DESIGN

Systematic review of studies comparing at least two concurrent groups of pregnant women with proved or likely acute toxoplasma infection in which treatments were compared with no treatment and outcomes in the children were reported.

SUBJECTS

Studies were identified from Medline (1966-97), Pascal (1990-7), Embase (1993-7), and Biological abstracts (1993-5) plus contact with experts in the field, including the European Research Network on Congenital Toxoplasmosis.

MAIN OUTCOME MEASURE

Proportion of infected children at 1 year born to infected pregnant women who were or were not treated.

RESULTS

Out of 2591 papers identified, nine met the inclusion criteria. There were no randomised comparisons, and control groups were generally not directly comparable with the treatment groups. Congenital infection was common in treated groups. five studies showed that treatment was effective and four that it was not.

CONCLUSION

It is unclear whether antenatal treatment in women with presumed toxoplasmosis reduces congenital transmission of Toxoplasma gondii. Screening is expensive, so the effects of treatment and impact of screening programmes need to be evaluated. In countries where screening or treatment is not routine, these technologies should not be introduced outside carefully controlled trials.

Mother-to-child transmission of toxoplasmosis: risk estimates for clinical counselling

BACKGROUND

Women who acquire toxoplasmosis infection during pregnancy (in most cases detected through serological screening) require counselling about the risk of congenital infection and its clinical sequelae. Reliable estimates of risk are not currently available. We undertook an analysis of data from women referred to the toxoplasmosis reference laboratory, Lyon, France, between 1987 and 1995.

METHODS

Information was collected from clinical notes kept at the laboratory and, where necessary, from the relevant obstetrician or paediatrician via telephone. Methods were developed to derive estimates of the risk of congenital toxoplasmosis by exact duration of gestation at maternal seroconversion.

FINDINGS

We analysed obstetric and paediatric data on 603 confirmed maternal toxoplasmosis infections. At least 564 women received antiparasitic drugs according to a standard protocol. Congenital infection status was ascertained in 554 cases, and infected children were followed-up for a median of 54 months. The overall maternal-fetal transmission rate was 29% (95% CI 25-33), which masked a sharp increase in risk with duration of gestation from 6% at 13 weeks to 72% at 36 weeks. However, fetuses infected in early pregnancy were much more likely to show clinical signs of infection. These effects counterbalance, and women who seroconverted at 24-30 weeks of gestation carried the highest risk (10%) of having a congenitally infected child with early clinical signs who was thus at risk of long-term complications.

INTERPRETATION

This information will assist the clinical counselling of pregnant women diagnosed with acute toxoplasmosis and may guide individual decisions on investigative and therapeutic options. Further studies are required to determine the long-term risks of clinical symptoms and disability due to congenital toxoplasmosis.

Feasibility of neonatal screening for toxoplasma infection in the absence of prenatal treatment. Danish Congenital Toxoplasmosis Study Group

BACKGROUND

The best method for prevention and control of congenital toxoplasma infection is uncertain. Prenatal screening is done in Austria and France, but the effect of treatment during pregnancy is not well documented. The aim of our study was to find out the maternofetal transmission rate and outcome in infants born to mothers who were not treated during pregnancy.

METHODS

We analysed 89873 eluates from phenylketonuria (PKU) cards from neonates and paired first-trimester serum samples from the mothers for specific IgG antibodies to Toxoplasma gondii. Children born to mothers who seroconverted during pregnancy were followed-up clinically and serologically to 12 months of age. In addition, 21144 PKU cards were analysed for toxoplasma-specific IgM antibodies during the last 12 months of the study.

FINDINGS

In 24989 (27.8%) cases both the PKU eluate and the first-trimester samples were IgG positive, which indicates previous maternal infection. 139 of the 64884 seronegative women acquired toxoplasma infection during pregnancy and gave birth to 141 infants (two sets of twins). 27 of these children were diagnosed with congenital toxoplasma infection. The transmission rate was 19.4% (95% CI 13.2-27.0). Clinical signs and symptoms were found in four (15%) of the 27 children. The additional analysis for toxoplasma-specific IgM antibodies from the PKU card identified seven of nine children with congenital toxoplasma infection. The false-positive rate for the IgM test was 0.19 per 1000, and no false-negatives were found.

INTERPRETATION

The risks of transmission of infection and of disease in the infant are low in an area with a low risk of toxoplasma infection. A neonatal screening programme based on detection of toxoplasma-specific IgM antibodies alone will identify between 70% and 80% of cases of congenital toxoplasmosis.

Epidemiological study of latent and recent infection by Toxoplasma gondii in pregnant women from a regional population in the U.K

AIMS

To determine the prevalence of IgG and IgM to Toxoplasma gondii (TG) and predict the incidence of infection during pregnancy and in foetuses.

METHODS

Thirteen thousand pregnant women from eastern England were tested at the time of booking for antenatal screening. Screening was carried out for the presence of IgG and IgM anti-TG, followed by confirmation with commercially available assays.

RESULTS

Latent infection to TG was found in 7.7% of women and increased with age from 6.8 to 17.8%. Recent infection accounted for an additional 0.4% equally distributed across age groups. No difference was found between urban and rural place of residence. A 1-2% incidence of TG infection every 5 years of age was found. IgM-only cases were mostly false positives and were unsuitable for statistical analysis. On the basis of both IgM and IgG imputed data, TG infection was found significantly higher during the first trimester of pregnancy. Three to sixteen TG-infected foetuses per 10000 pregnancies were predicted.

CONCLUSIONS

The east of England has a low prevalence of TG infection and therefore a high, at-risk population of pregnant women. Repeated screening during pregnancy would be expensive, but would detect and possibly prevent infection in approximately 10 neonates per 10000 women.

Toxoplasmosis and parvovirus B19

Pregnant women might well improve their chances for a successful pregnancy outcome by following the advice of W. C. Fields: avoid contact with small children and animals whenever possible. Failing widespread acceptance of this philosophy, management of T. gondii and parvovirus B19 infections continues to be a challenge for the foreseeable future.

Low incidence of congenital toxoplasmosis in children born to women infected with human immunodeficiency virus. European Collaborative Study and Research Network on Congenital Toxoplasmosis

In children born to immunocompetent women, congenital toxoplasmosis almost always results from primary infection during pregnancy. However, reactivation of latent toxoplasmosis during pregnancy could occur in HIV-infected pregnant women, particularly in those who are severely immunocompromised, and result in maternal-fetal transmission of the parasite. This mode of infection has been described in case reports but the risk of transmission is unknown. Findings on toxoplasmosis are presented from the European Collaborative Study, a prospective study of children born to women known to be HIV-infected at the time of delivery. In 1058 children followed for a mean duration of 35 months, only one child developed clinical toxoplasmosis. This child was HIV-infected, severely immunocompromised, and acquired toxoplasmosis postnatally. Congenital infection was excluded serologically in a subgroup of 167 children, of whom an estimated 71 had been at risk of infection. These clinical and serological findings indicate a low general risk of maternal-fetal transmission of Toxoplasma infection in HIV-infected women. It is not possible to draw conclusions about the risk of transmission for severely immunocompromised HIV-infected women because most women in the study were asymptomatic.

A cost-benefit analysis of prenatal screening for toxoplasmosis

The objective of this study was to examine critically the validity of a toxoplasma prenatal screening program, in the context of a cost-benefit analysis, as it relates to the Canadian experience. Recently, studies have suggested that early treatment of infected infants with a combination of pyrimethamine and sulfadiazine is effective in reducing the sequelae of toxoplasmosis. It was concluded that a carefully planned screening program for detecting and treating infants infected with Toxoplasma gondii during pregnancy is cost beneficial. The cost of delivering a screening and treatment program is less than half of what it would cost to provide comprehensive long term medical, educational and other social services for the estimated 1000 children born each year with congenital toxoplasmosis. Even if an incidence as low as two infected infants per 1000 pregnancies is assumed and only 400 children were affected, the screening and preventive therapy program would be justified.

La toxoplasmose chez la femme enceinte en France : séroprévalence, taux de séroconversion et niveau de connaissance des mesures préventives. Tendances 1965–1995

The main trends and the significant points concerning the evolution of seroprevalence, seroconversion's rate and knowledge's level of preventive measures against toxoplasmosis in pregnant women in France are : a progressive decrease of immunisation's ratio with regional variation (national mean is estimated at 54 % in 1995); diversity of factors having a potential influence on the contamination, the trends of most of them tend to decrease the contamination but the exact impact is difficult to appreciate; stability of seroconversion's rate since 15 years 4 to 5 p.1000 of the whole pregnancy for nine months exposition period; ways of contamination are still the same; few informations about knowledge's level concerning preventives measures and performances of educative action.

Screening for toxoplasmosis in pregnancy: what is the evidence of reducing a health problem?

OBJECTIVES

Toxoplasma gondii is a parasite which may give rise to congenital infection. Screening pregnant women for antibodies against toxoplasmosis is being debated in many countries. The preventive impact of toxoplasmosis screening of pregnant women depends on the magnitude of disease caused by congenital toxoplasmosis (incidence x transmission rate to fetus x diseased proportion of infected children), on the one hand, and the preventable proportion of disease (sensitivity of the screening test x efficacy of the treatment x compliance), on the other. In this study the preventive impact of screening pregnant women for toxoplasmosis antibodies is assessed by letting the value for these variables change within reasonable limits.

METHODS

To obtain information on these variables, relevant publications were reviewed in the Medline database from 1983 to February 1996 and the Cochrane Pregnancy and Childbirth Database. References in review articles on congenital toxoplasmosis were also studied.

RESULTS

The literature review showed that no population based prospective studies of the natural history of toxoplasmosis infection during pregnancy, nor any randomised controlled trials of the efficacy of antiparasitic treatment, had been carried out. In the empirical studies which have been performed the values of most variables show considerable differences. According to these values, the estimates in this study of the impact of toxoplasmosis screening in pregnancy may range from 0 to 40 children in whom disease is preventable per 100,000 pregnant women susceptible to toxoplasmosis infection.

CONCLUSION

Sufficient scientific evidence is not yet available to propose screening for toxoplasmosis in pregnant women, and efforts should be made to provide such knowledge. Also, the magnitude of the negative impact of screening, such as induced abortion of healthy fetuses, anxiety in women with false positive screening tests, and side effects of treatment, has not been sufficiently examined.

Congenital toxoplasmosis: prevention, screening and treatment

Congenital toxoplasmosis is an established cause of abortion, neonatal disease and ocular defects presenting in later life. Preventative options include health education, immunization and screening of pregnant women and infants with appropriate management of cases found to be at risk. Screening requires a knowledge of the disease, the test, the treatment and the administration of the proposed programme. Treatment can be directed towards the acutely infected mother, the infected fetus or infant and the patient with an acute exacerbation of ocular toxoplasmosis following congenital infection. Harm-benefit assessment of screening programmes designed to prevent congenital toxoplasmosis has produced conflicting results. Further research is required into the incidence of acute toxoplasmosis in pregnancy and subsequent congenital infection, the frequency of neonatal handicap, precise tests for the diagnosis of recent maternal infection and the presence of congenital toxoplasmosis and improved treatment of the infection.

Prenatal diagnosis of congenital toxoplasmosis with a polymerase-chain-reaction test on amniotic fluid

BACKGROUND

Congenital infection with Toxoplasma gondii can produce serious sequelae. However, there is little consensus about screening during pregnancy, and the tests used to establish a prenatal diagnosis of toxoplasmosis are complex and slow. We evaluated a simpler approach that is based on a polymerase-chain-reaction (PCR) test.

METHODS

Prenatal diagnostic tests, including ultrasonography, amniocentesis, and fetal-blood sampling, were performed in 2632 women with T. gondii infection acquired during pregnancy. In 339 consecutive women, a competitive PCR test for T. gondii was performed on amniotic fluid, and its results were compared with those of conventional diagnostic tests. The PCR test targets the B1 gene of T. gondii, uses an internal control, and can be completed in a day. Positive tests were confirmed by serologic testing of newborns or by autopsy in terminated pregnancies.

RESULTS

Overall, the risk of fetal infection was 7.4 percent, but it increased sharply with gestational age. Congenital infection was demonstrated in 34 of 339 fetuses by conventional methods, and the PCR test was positive in all 34. In three other fetuses, only the PCR test gave positive results, and follow-up testing confirmed the presence of congenital toxoplasmosis. The PCR test gave one false negative result but no false positive results. The PCR test performed better than conventional parasitologic methods (sensitivity, 97.4 vs. 89.5 percent; negative predictive value, 99.7 vs. 98.7 percent).

CONCLUSIONS

For the prenatal diagnosis of congenital T. gondii infection, an approach based on a PCR test performed on amniotic fluid is rapid, safe, and accurate.

Management of toxoplasmosis

Toxoplasma gondii, an intracellular coccidian protozoan, is the causative agent of toxoplasmosis, a widespread infection affecting various birds and mammals including humans. In immunocompetent hosts, the infection is usually asymptomatic and benign. Toxoplasmosis is either congenital or acquired. In general, prenatal therapy of congenital toxoplasmosis is beneficial in reducing the frequency of infant infection. Therapies are based primarily on spiramycin because of the relative lack of toxicity and high concentrations achieved in the placenta. Clindamycin is the standard drug for chemoprophylaxis in newborn infants, and is directed at preventing the occurrence of retinochoroiditis as a late sequel to congenital infection. The standard treatment for acquired toxoplasmosis in both immunocompetent and immunodeficient patients is the synergistic combination of pyrimethamine and sulphonamides. Toxoplasmic encephalitis is the most common manifestation of acquired toxoplasmosis in immunocompromised patients and if not treated is fatal. However, because of toxicity, the therapeutic efficacy of pyrimethamine-sulphonamide combinations may be seriously limited in immunodeficient patients. A number of novel and less toxic agents are being currently studied in clinical settings, including macrolide antibiotics (clindamycin, clarithromycin and azithromycin) and atovaquone, as well as some older anti-infective drugs such as cotrimoxazole (trimethoprim/sulfamethoxazole). Maintenance or prophylactic therapy is essential in many patients with acquired immunodeficiency syndrome (AIDS) where toxoplasmosis is most often the result of a pre-existent latent infection.

Ocular involvement in toxoplasmosis

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Toxoplasmosis in pregnancy

Primary infection with Toxoplasma gondii in pregnant women occurs all over the world with frequencies between 0.1-1%. In approximately 40% of the cases, the unborn child is infected. The risk of fetal infection increases during pregnancy, while at the same time the risk of severe disease decreases. As a result, infants with congenital toxoplasmosis are mostly asymptomatic at birth, but long-term studies indicate that up to 85% of them will develop sequelae including chorioretinitis (leading to severe impairment of vision), hearing loss or mental retardation. Early recognition of maternal infection and treatment with spiramycin or pyrimethamine-sulphadiazine will reduce the parasitic colonization of the placenta by more than 60% and prevent infection in the fetus. If fetal infection has already occurred, maternal treatment modifies the fetal disease. Therapy during the first year of life improves the prognosis. It is possible today to identify infected fetuses by prenatal diagnosis based on detection of the parasite in cord blood, amniotic fluid and placental tissue. Specific antibodies and non-specific signs of infection in fetal blood give additional information. Advances in laboratory techniques have made it feasible to consider serological surveillance of pregnant women. The present recommendation is that each country should provide data on the incidence of toxoplasma infection in pregnancy and thereby decide whether it represents a problem and what measures should be adopted. This paper summarizes the present knowledge of the parasite and its implication for the mother and unborn child. The effect and problems of primary and secondary prevention in pregnancy are discussed as well as the efficacy of treatment. The need for future research including long-term follow-up studies are emphasized.

Diagnostic and therapeutic dilemmas in ocular toxoplasmosis

Ocular toxoplasmosis, a leading cause of visual handicaps in young people, represents a late manifestation of congenital infection in the majority of cases. Ocular involvement in acquired toxoplasmosis has been repeatedly reported and shows that toxoplasmic retinitis may develop in the wake of acquired infection. The diagnosis of ocular toxoplasmosis is mainly clinical since serologic tests are positive for a considerable percentage of the general population and are not indicative for ocular involvement. The demonstration of local synthesis of toxoplasma antibodies in the eye by intraocular fluid analysis is a valuable diagnostic tool. The application of the polymerase chain reaction, in which the parasite's DNA is detected, may be expected to change the diagnostic repertoire drastically in the future. The need for appropriate therapy for patients with ocular toxoplasmosis is a matter of continued debate: the majority of the medications used for treatment have potentially serious side effects and the efficacy of treatments has not been clarified in previous studies. Recently, a prospective multicenter study to evaluate the efficacy of current therapeutic strategies for ocular toxoplasmosis was performed in The Netherlands and included 106 patients with active ocular toxoplasmosis. The principal conclusion of this study is that only drug therapy with pyrimethamine had any perceptible influence on any aspect of ocular toxoplasmosis, but this effect may not be worth the risk of side effects except in fovea threatening lesions.

Congenital toxoplasmosis

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Prevalence of infections affecting the child among pregnant women in Yaounde, Cameroon

The prevalence of infections which have deleterious effects to either the mother or the fetus during pregnancy are unknown in Cameroon. To formulate appropriate antenatal screening policies for the Central Mother and Child Clinic in Yaounde, we tested random sera obtained from 1,014 stored samples previously obtained from pregnant women. One hundred and fifty sera were tested for the presence of the hepatitis B surface antigen (HBsAg), 544 for syphilis antibodies, 192 for antibodies to rubella and 192 for antibodies to Toxoplasma gondii. We found the HBsAg in 25.3% (38/150) of the subjects, antibodies against syphilis in 15.9% (87/544), antibodies to the rubella virus in 83.9% (161/192) and evidence of toxoplasma infection in 77.1% (148/192). Of the 38 HBsAg-positive subjects, 5.2% and 55.3% were positive for the HBe antigen and HBe antibody, respectively. We found a high prevalence for these infections in the antenatal clinical attendants. The data will be used to develop an appropriate control strategy for them.

Incidence of primary toxoplasma infections during pregnancy in southern Finland: a prospective cohort study

Congenital toxoplasmosis may develop after maternal primary infection during pregnancy. Since toxoplasmosis in adults is usually asymptomatic, the only way to find the pregnancies at risk of acute toxoplasmosis (i.e. seronegative mothers) is to perform serological screening of all pregnant women. We studied toxoplasma-specific antibodies in 16,733 pregnant women in the first, second, and third trimesters over an 18-month period in the Helsinki area, with a population of 820,700. The participation rate in our study was 90.2% of all pregnancies in the area. The overall prevalence of toxoplasma seropositivity was 20.3%. The incidence of primary infection was 2.4/1000 pregnancies at risk. Our data on incidence suggest an annual occurrence of 131 cases of primary toxoplasma infections during pregnancy in Finland. Primary toxoplasma infection appears to be a significant risk to the fetus even in countries where the prevalence of toxoplasma seropositivity is low. The feasibility of mass screening for toxoplasma infections during pregnancy should be considered in order to reduce the morbidity and mortality due to congenital toxoplasmosis.

Incidence of congenital toxoplasmosis in the Republic of Slovenia

Over a 12-month period, 3959 pregnant women were systematically tested with the Sabin-Feldman dye test in order to assess the incidence of congenital toxoplasmosis in Slovenia. The results suggest that this is approximately 3/1000 live births. This relatively high incidence of congenital toxoplasmosis in Slovenia may make the costing of preventive screening programmes justifiable.

Congenital toxoplasmosis: a large survey in western Australia

OBJECTIVE

To determine the birth prevalence of congenital toxoplasmosis in Western Australia.

DESIGN

A prospective serological study of randomly selected pregnant women and their newborn infants. Paired sera collected from the mothers at their first antenatal visit and cord blood specimens taken from their infants were tested for toxoplasmosis by the direct agglutination test and Toxoplasma IgM-capture enzyme-linked immunosorbent assay.

SETTING

A major Perth metropolitan obstetric teaching hospital where approximately one-quarter of infants born in Western Australia during January 1986 to December 1989 inclusive were delivered.

PARTICIPANTS

Sera were obtained from 10,207 pregnant women presenting for routine clinical evaluation at their first antenatal visit. Cord blood specimens were taken from 18,908 infants; 7523 of these could be paired to maternal specimens.

MAIN OUTCOME MEASURES

Maternal infection was indicated in cases where Toxoplasma specific IgM antibody was present or where an initial maternal specimen gave negative results for Toxoplasma antibody but the paired cord blood specimen gave positive results. Toxoplasma specific IgM antibody in a cord blood specimen indicated fetal infection.

RESULTS

Of the 10,207 women 3544 (35%) were Toxoplasma immune at their first antenatal visit; in 11 Toxoplasma specific IgM antibody was detected. There was no serological or clinical evidence of congenital toxoplasmosis in any of the offspring of these 11 mothers. The rate of maternal infection in susceptible pregnancies was 1.6 per 1000; the maternal-fetal transmission rate was estimated to be no greater than 24%. Three of the 18,908 cord blood specimens tested gave positive results for Toxoplasma specific IgM antibody giving a birth prevalence of congenital infection of 0.23 per 1000 births to non-immune mothers. There were no clinical features of congenital infection in these three infants but they will require long-term follow-up. Thirteen of the 14 mothers infected during pregnancy were interviewed retrospectively and in only three was a known risk factor for infection present.

CONCLUSIONS

a toxoplasmosis screening programme for pregnant mothers is not justifiable in Western Australia. A public education programme is also likely to have limitations.