Congenital toxoplasmosis

Maternal Toxoplasma gondii infection affects proliferation, differentiation and cell cycle regulation of retinal neural progenitor cells in mouse embryo

Background

Toxoplasmosis affects one third of the world population and has the protozoan Toxoplasma gondii as etiological agent. Congenital toxoplasmosis (CT) can cause severe damage to the fetus, including miscarriages, intracranial calcification, hydrocephalus and retinochoroiditis. Severity of CT depends on the gestational period in which infection occurs, and alterations at the cellular level during retinal development have been reported. In this study, we proposed a mouse CT model to investigate the impact of infection on retinal development.

Methods

Pregnant females of pigmented C57BL/6 strain mice were infected intragastrically with two T. gondii cysts (ME49 strain) at embryonic day 10 (E10), and the offspring were analyzed at E18.

Results

Infected embryos had significantly smaller body sizes and weights than the PBS-treated controls, indicating that embryonic development was affected. In the retina, a significant increase in the number of Ki-67-positive cells (marker of proliferating cells) was found in the apical region of the NBL of infected mice compared to the control. Supporting this, cell cycle proteins Cyclin D3, Cdk6 and pChK2 were significantly altered in infected retinas. Interestingly, the immunohistochemical analysis showed a significant increase in the population of β-III-tubulin-positive cells, one of the earliest markers of neuronal differentiation.

Conclusions

Our data suggests that CT affects cell cycle progression in retinal progenitor cells, possibly inducing the arrest of these cells at G2/M phase. Such alterations could influence the differentiation, anticipating/increasing neuronal maturation, and therefore leading to abnormal retinal formation. Our model mimics important events observed in ocular CT.

Infection of Mouse Neural Progenitor Cells by Toxoplasma gondii Reduces Proliferation, Migration, and Neuronal Differentiation in Vitro

Congenital toxoplasmosis constitutes a major cause of pre- and postnatal complications. Fetal infection with Toxoplasma gondii influences development and can lead to microcephaly, encephalitis, and neurologic abnormalities. Systematic studies concerning the effects of neural progenitor cell infection with T. gondii are unavailable. Cortical intermediate progenitor cells cultivated as neurospheres obtained from E16.5 Swiss Webster mice were infected with T. gondii (ME49 strain) tachyzoites to mimic the developing mouse cerebral cortex in vitro. Infection was associated with decreased cell proliferation, detected by Ki-67 staining at 48 and 72 hours after infection in floating neurospheres, and reduced cellularity at 96 hours. Transient decreases in the expression of the neurogenesis-related transcription factors T-box brain protein 1, mouse atonal homolog protein 1, and hairy and enhancer of split protein 1 were found in infected cultures, while the level of transcription factor SOX-2 remained unaltered. Neurogenic potential, assessed in plated neurospheres, was impaired in infected cultures, as indicated by decreased late neuronal marker neurofilament heavy chain immunoreactivity. Infected cultures exhibited decreased overall migration rates at 48 and 120 hours. These findings indicate that T. gondii infection of neural progenitor cells may lead to reduced neurogenesis due to an imbalance in cell proliferation alongside an altered migratory profile. If translated to the in vivo situation, these data could explain, in part, cortical malformations in congenitally infected individuals.

Anti-Toxoplasma gondii IgM Long Persistence: What Are the Underlying Mechanisms?

Diagnosis of Toxoplasma gondii acute infection was first attempted by detection of specific IgM antibodies, as for other infectious diseases. However, it was noted that this immunoglobulin declines slowly and may last for months or even years. Apart from the diagnostic problem imposed on clinical management, this phenomenon called our attention due to the underlying phenomena that may be causing it. We performed a systematic comparison of reports studying IgM antibody kinetics, and the data from the papers were used to construct comparative plots and other graph types. It became clear that this phenomenon is quite generalized, and it may also occur in animals. Moreover, this is not a technical issue, although some tests make more evident the prolonged IgM decay than others. We further investigated biological reasons for its occurrence, i.e., infection dynamics (micro-reactivation–encystment, reinfection and reactivation), parasite strain relevance, as well as host innate, natural B cell responses and Ig class-switch problems inflicted by the parasite. The outcomes of these inquiries are presented and discussed herein.

Implications of TORCH Diseases in Retinal Development-Special Focus on Congenital Toxoplasmosis

There are certain critical periods during pregnancy when the fetus is at high risk for exposure to teratogens. Some microorganisms, including Toxoplasma gondii, are known to exhibit teratogenic effects, interfering with fetal development and causing irreversible disturbances. T. gondii is an obligate intracellular parasite and the etiological agent of Toxoplasmosis, a zoonosis that affects one third of the world's population. Although congenital infection can cause severe fetal damage, the injury extension depends on the gestational period of infection, among other factors, like parasite genotype and host immunity. This parasite invades the Central Nervous System (CNS), forming tissue cysts, and can interfere with neurodevelopment, leading to frequent neurological abnormalities associated with T. gondii infection. Therefore, T. gondii is included in the TORCH complex of infectious diseases that may lead to neurological malformations (Toxoplasmosis, Others, Rubella, Cytomegalovirus, and Herpes). The retina is part of CNS, as it is derived from the diencephalon. Except for astrocytes and microglia, retinal cells originate from multipotent neural progenitors. After cell cycle exit, cells migrate to specific layers, undergo morphological and neurochemical differentiation, form synapses and establish their circuits. The retina is organized in nuclear layers intercalated by plexus, responsible for translating and preprocessing light stimuli and for sending this information to the brain visual nuclei for image perception. Ocular toxoplasmosis (OT) is a very debilitating condition and may present high severity in areas in which virulent strains are found. However, little is known about the effect of congenital infection on the biology of retinal progenitors/ immature cells and how this infection may affect the development of this tissue. In this context, this study reviews the effects that congenital infections may cause to the developing retina and the cellular and molecular aspects of these diseases, with special focus on congenital OT.

Antenatal screening for Toxoplasma gondii infection at a tertiary care hospital in Riyadh, Saudi Arabia

BACKGROUND AND OBJECTIVES

Congenital toxoplasmosis is associated with significant morbidity and mortality. This study investigates the prevalence of toxoplasmosis among pregnant women.

DESIGN AND SETTING

A retrospective study at King Khalid University Hospital, Riyadh from September 2009 to August 2010.

PATIENTS AND METHODS

0 Laboratory data of 2176 pregnant women screened for Toxoplasma gondii in the antenatal care unit were assessed during the study period. The mean (SD) age of the women and the duration of pregnancy were 25 (7.3) years and 18 (7.7) weeks, respectively. Data were extracted for the presence or absence of anti-T gondii immunoglobulin G (IgG) and IgM antibodies.

RESULTS

Of 2176 sera tested, 1351 (62%) did not show any evidence of exposure to T gondii. The remaining 825 (38%) samples tested positive for anti-T gondii IgG antibodies, and none was found to have anti-T gondii IgM antibodies in the serum. These data reveal that a significantly high number of women in the antenatal care unit at King Khalid University Hospital in Riyadh had been exposed to T gondii.

CONCLUSION

A high prevalence of toxoplasmosis among pregnant women warrants multicenter community-based investigations for assessment of T gondii infection and identification of risk factors for transmission of toxoplasmosis in general, and particularly during pregnancy.

Symptomatic toxoplasma infection due to congenital and postnatally acquired infection

AIMS

To determine the incidence and severity of symptomatic toxoplasma infection presenting during childhood due to congenital or postnatally acquired infection.

METHODS

Between 2002 and 2004, newly diagnosed children (<16 years) with signs or symptoms of congenital or ocular toxoplasmosis were reported by clinicians to the British Paediatric and Ophthalmic Surveillance Units or by toxoplasma referral laboratories. Confirmed cases were estimated to have a greater than 50% probability of congenital and/or ocular toxoplasmosis, based on clinical and serological findings.

RESULTS

Thirty eight children had confirmed toxoplasma infection. Twenty two (58%) were classified with congenital infection (cumulative incidence for England and Wales 1.62[corrected]/100,000 live births; 95% CI 0.85[corrected] to 2.83[corrected]), of whom 2 (9%) were stillborn, 7 (32%) live births had intracranial abnormalities and/or developmental delay (5 of whom had retinochoroiditis), and 10 (45%) had retinochoroiditis with no other abnormalities reported. A further 16 (42%) children were classified as infected after birth; all had retinochoroiditis.

CONCLUSIONS

The low burden of symptomatic congenital toxoplasmosis combined with the lack of evidence of an effective treatment support current policy not to offer prenatal or neonatal screening for toxoplasma infection. Primary prevention strategies need to address acquisition of infection in childhood which accounts for half the ocular disease due to toxoplasma infection in children in the UK and Ireland.

TORCH test for fetal medicine indications: only CMV is necessary in the United Kingdom

OBJECTIVES

To review the indications and value of TORCH testing (toxoplasma, rubella, cytomegalovirus, herpes) for fetal medicine reasons.

METHODS

Analysis of all maternal and fetal TORCH tests requested from a busy Fetal Medicine Unit during nearly a 10-year period. The main ultrasound findings considered as possibly caused by congenital fetal infections were analysed. Pregnancy outcomes for cases with confirmed maternal or fetal infections were studied.

RESULTS

Four hundred and sixty-two maternal TORCH tests were performed. Of those, TORCH tests were also performed on fetal samples (amniotic fluid or fetal blood) in 67 cases. Fourteen fetal tests without maternal testing were identified, making the total number of patients tested 476. There were 11 cases of maternal CMV infection (2.3%), 10 cases of fetal CMV infection, and none of the other viruses. Indications for testing included fetal hyperechogenic bowel, hydrops, cerebral ventriculomegaly, echogenic foci, oligohydramnios, polyhydramnios, and IUGR. The most common findings to be actually associated with fetal infections were hyperechogenic bowel, ascites, cardiomegaly, and oligohydramnios. No cases were associated with polyhydramnious, while both IUGR and ventriculomegaly were always associated with other more relevant features.

CONCLUSION

In the United Kingdom, complete maternal TORCH testing because of fetal findings on detailed scans is often not necessary. Testing can be limited only to CMV, particularly since other infectious agents, including toxoplasmosis, are uncommon in the United Kingdom. More understanding of the relevance of the different ultrasound features to congenital infections is also important.

[Seroprevalence of toxoplasmosis in women of childbearing age, 1992-1999]

To determine the need of prenatal screening for toxoplasmosis in our hospital from a seroepidemiological point of view.

PATIENTS AND METHODS

The prevalence of IgG anti-T. gondii was retrospectively analyzed in 7.090 women of childbearing age attended in the Hospital Clínic of Barcelona from February 1992 to April 1999. The association among the seroprevalence and the variables year, age, birthplace (province of Barcelona/other provinces) and place of residence (urban/rural) was analyzed. A decreasing trend was observed in the prevalence (p < 0.001), currently being < 40% in the average women between 15 and 45 years. Infection was also directly related to age of women (p < 0.001) and birthplace out of the province of Barcelona (p = 0.001). Habitat (rural or urban) was not associated with seroprevalence. Prenatal screening for toxoplasmosis is necessary due to the high rate of seronegative women exposed to infection and the evidence of a high number of primoinfections in the childbearing period.

Sources of toxoplasma infection in pregnant women: European multicentre case-control study. European Research Network on Congenital Toxoplasmosis

OBJECTIVE

To determine the odds ratio and population attributable fraction associated with food and environmental risk factors for acute toxoplasmosis in pregnancy.

DESIGN

Case-control study.

SETTING

Six large European cities.

PARTICIPANTS

Pregnant women with acute infection (cases) detected by seroconversion or positive for anti-Toxoplasma gondii IgM were compared with pregnant women seronegative for toxoplasma (controls).

MAIN OUTCOME MEASURES

Odds ratios for acute infection adjusted for confounding variables; the population attributable fraction for risk factors.

RESULTS

Risk factors most strongly predictive of acute infection in pregnant women were eating undercooked lamb, beef, or game, contact with soil, and travel outside Europe and the United States and Canada. Contact with cats was not a risk factor. Between 30% and 63% of infections in different centres were attributed to consumption of undercooked or cured meat products and 6% to 17% to soil contact.

CONCLUSIONS

Inadequately cooked or cured meat is the main risk factor for infection with toxoplasma in all centres. Preventive strategies should aim to reduce prevalence of infection in meat, improve labelling of meat according to farming and processing methods, and improve the quality and consistency of health information given to pregnant women.

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.

Status of toxoplasma antibodies in recurrent fetal loss in U.A.E. women

A retrospective analysis to determine the status of toxoplasma (IgG & IgM) antibodies in UAE women with recurrent fetal loss was done using immunofluorescence assay. Two thousand three hundred and fourty three patients with one or more fetal loss were studied over a period of five years. In patients with fetal loss, the range of toxoplasma IgG seropositivity varied from 24.2-30.6%. There were 3 patients with IgM positive. Only in a single patient one of her two abortions could be attributed to acute toxoplasmosis. Habitual fetal loss cannot be attributed to chronic toxoplasmosis. Also, 67.2% of the women of child bearing age group in U.A.E were found to be seronegative, highlighting the need for routine antenatal screening to detect primary acute toxoplasmosis.

Antenatal screening for Down's syndrome

BACKGROUND

In 1968 the first antenatal diagnosis of Down's syndrome was made and screening on the basis of selecting women of advanced maternal age for amniocentesis was gradually introduced into medical practice. In 1983 it was shown that low maternal serum alpha fetoprotein (AFP) was associated with Down's syndrome. Later, raised maternal serum human chorionic gonadotrophin (hCG), and low unconjugated oestriol (uE3) were found to be markers of Down's syndrome. In 1988 the three biochemical markers were used together with maternal age as a method of screening, and this has been widely adopted. PRINCIPLES OF ANTENATAL SCREENING FOR DOWN'S SYNDROME: Methods of screening need to be fully evaluated before being introduced into routine clinical practice. This included choosing markers for which there is sufficient scientific evidence of efficacy, quantifying performance in terms of detection and false positive rates, and establishing methods of monitoring performance. Screening needs to be provided as an integrated service, coordinating and managing the separate aspects of the screening process. SERUM MARKERS AT 15-22 WEEKS OF PREGNANCY: A large number of serum markers have been found to be associated with Down's syndrome between 15 and 22 weeks of pregnancy. The principal markers are AFP, hCG or its individual subunits (free alpha- and free beta-hCG), uE3, and inhibin A. Screening performance varies according to the choice of markers used and whether ultrasound is used to estimate gestational age (table 1). When an ultrasound scan is used to estimate gestational age the detection rate for a 5% false positive rate is estimated to be 59% using the double test (AFP and hCG), 69% using the triple test (AFP, hCG, uE3), and 76% using the quadruple test (AFP, hCG, uE3, inhibin A), all in combination with maternal age. Other factors that can usefully be taken into account in screening are maternal weight, the presence of insulin dependent diabetes mellitus, multiple pregnancy, ethnic origin, previous Down's syndrome pregnancy, and whether the test is the first one in a pregnancy or a repeat. Factors such as parity and smoking are associated with one or more of the serum markers, but the effect is too small to justify adjusting for these factors in interpreting a screening test.

URINARY MARKERS AND FETAL CELLS IN MATERNAL BLOOD

Urinary beta-core hCG has been investigated in a number of studies and shown to be raised in pregnancies with Down's syndrome. This area is currently the subject of active research and the use of urine in future screening programmes may be a practical possibility. Other urinary markers, such as total oestriol and free beta-hCG may also be of value. Fetal cells can be identified in the maternal circulation and techniques such as fluorescent in situ hybridisation can be used to identify aneuploidies, including Down's syndrome and trisomy 18. This approach may, in the future, be of value in screening or diagnosis. Currently, the techniques available do not have the performance, simplicity, or economy needed to replace existing methods.

DEMONSTRATION PROJECTS

Demonstration projects are valuable in determining the feasibility of screening and in refining the practical application of screening. They are of less value in determining the performance of different screening methods. Several demonstration projects have been conducted using the triple and double tests. In general, the uptake of screening was about 80%. The screen positive rates were about 5-6%. About 80% of women with positive screening results had an invasive diagnostic test, and of those found to have a pregnancy with Down's syndrome, about 90% chose to have a termination of pregnancy. ULTRASOUND MARKERS AT 15-22 WEEKS OF PREGNANCY: There are a number of ultrasound markers of Down's syndrome at 15-22 weeks, including nuchal fold thickness, cardiac abnormalities, duodenal atresia, femur length, humerus length, pyelectasis, and hyperechogenic bowel. (ABSTRA

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.

The investigation of toxoplasma infection associated with pregnancy

An audit was undertaken to determine case compliance with prenatal testing and investigation of infants for toxoplasma infection. Subsequently, the effect of enhanced reference unit Intervention was studied. The proportion of cases of toxoplasma infection associated with pregnancy completing an investigation programme was calculated. The effect of continued and short-term additional intervention was assessed and reasons for failure to comply were sought. The status of the child was established in 30% of cases when acute maternal toxoplasma infection was detected. Continuous reference unit intervention significantly improved case compliance to 45% over a 3-year period, but the effect was lost when the additional measures were withdrawn. Failure to complete the investigation procedure was associated with loss of patient-clinician contact and clinician/laboratory error. Enhanced intervention did not result in a significant improvement in compliance with the investigation programme for babies with clinical abnormality. The benefits of testing for toxoplasma infection associated with pregnancy are limited by failure to complete necessary investigations.

Urine sample used for congenital toxoplasmosis diagnosis by PCR

The diagnosis of toxoplasmosis in congenitally infected infants can be difficult; serology is unreliable, and diagnosis must be based on the combination of symptomatology and direct demonstration of the parasite. Four infants suspected of having Toxoplasma gondii infection were studied by serological analysis, tissue culture, and PCR determination. T. gondii was isolated from the urine of one patient. The parasite was detected by PCR in the blood and cerebrospinal fluid of three infants and in the urine in all patients. Because nested PCR proved to be a sensitive, relatively rapid, and specific method and because it can be applied to a variety of different clinical samples, PCR can be a valuable technique for the identification of T. gondii infections in children. The present study indicates that PCR examination of urine, a fluid never before used for diagnosis in this age group, may be valuable in diagnosing cases of congenital toxoplasmosis.

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.

Diagnostic implications of kinetics of immunoglobulin M and A antibody responses to Toxoplasma gondii

We evaluated immunoglobulin M (IgM) and IgA assays that could improve the predictive value for recently acquired toxoplasma infection for patients with positive screening test results. Follow-up sera were collected from 82 patients whose initial serum specimen had a reactive anti-Toxoplasma gondii IgM result. According to the evolution of the immune response, patients were divided retrospectively into two groups: one in which a recent infection was unlikely and the other one with an evolving immune response suggestive of recent toxoplasma infection. All IgM and one of three IgA assays used in the study are suitable for screening pregnant patients, with a negative predictive value of 100%. The predictive value of positive results is much lower because of the low prevalence of acute toxoplasmosis in pregnant women and the long persistence of IgM after acute infection. In the present study, all except one IgM enzyme immunoassay remained positive well beyond 6 months after the initial sample was tested. The IgM immunofluorescence test had the shortest persistence of positivity in most cases. IgA tests were either too insensitive or remained reactive too long to be useful for screening pregnant patients. Interpreting enzyme immunoassays with modified cutoff values and the combination of two tests could improve the predictive value of positive results to about 80% in terms of recent infection.

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.

Incidence of acute symptomatic toxoplasma retinochoroiditis in south London according to country of birth

OBJECTIVE

To determine the incidence of acute symptomatic toxoplasma retinochoroiditis presenting to ophthalmologists for patients born in Britain and elsewhere.

DESIGN

Population based, cross sectional study.

SETTING

11 districts in south Greater London.

SUBJECTS

All patients presenting to NHS ophthalmologists with symptoms due to acute toxoplasma retinochoroiditis in 1992-3.

MAIN OUTCOME MEASURE

Intraocular inflammation in association with a retinochoroidal scar, active adjoining retinitis, and IgG serum antibodies to toxoplasma.

RESULTS

The estimated incidence of acute symptomatic retinochoroiditis for all people born in Britain was 0.4/100,000/year. If a mean of two symptomatic episodes per lifetime is assumed, 100 people born in Britain may be affected each year, about a fifth of the estimated 500-600 congenitally infected people born each year.

CONCLUSIONS

A substantial proportion of people with acute symptomatic toxoplasma retinochoroiditis were born outside the country, and the number born in Britain was smaller than the number previously estimated to develop retinochoroidal lesions due to congenital toxoplasmosis. These findings suggest that prenatal screening for toxoplasmosis in Britain may be of limited benefit.

Host-parasite relationship between congenital Toxoplasma infection and mouse brain: role of small vessels

Small vessels showing inflammatory cell infiltrates were invariably observed in the vicinity of intact Toxoplasma tissue cysts within the brains of mice congenitally infected with the protozoan. Lymphocytes were observed in intimate contact with the luminal aspect of the endothelium, penetrating into the thickened basal lamina and in the perivascular area, which also contained macrophages and neutrophilic granulocytes. Rarely, lymphocytes were observed attached to the outer membrane of the host neurone which contained a Toxoplasma tissue cyst and within the inflammatory infiltrate associated with a disintegrating cyst. An hypothesis is presented which combines these morphological observations to explain the events associated with tissue cyst associated recrudescence of latent Toxoplasma infection in mouse brain.

Cost-benefit analysis of screening for toxoplasmosis during pregnancy

Congenital toxoplasmosis is a risk for fetus both in 'low' and 'high risk' areas. A cost-benefit analysis based on data from a Finnish prospective study (20.3% seropositivity of pregnant mothers and incidence of 2.4/1,000 seronegative pregnancies) and on Finnish cost data was performed to compare the no-screening and screening alternatives for primary toxoplasma infections during pregnancy. A maternal-feto transmission risk of 40%, effectiveness of treatment of 50%, and discount rate of 4% were used as other baseline probabilities. The calculations were carried out by decision analysis combined with sensitivity analysis. The total annual costs of congenital toxoplasmosis without screening amount to US$ 128/pregnancy/year, and with systematic serological screening, US$ 95/pregnancy. Thus screening reduces the costs by 25%. The present value of net savings in Finland would be US$ 2.1 million every year. A one-way sensitivity analysis showed that screening together with health education is preferable to health education without screening if the incidence of maternal primary infections exceeds 1.1/1,000 and effectiveness of treatment is better than 22.1%. Screening for toxoplasma infections during pregnancy is economically worthwhile even in a country with a low incidence. A scheme of systematic screening for maternal primary toxoplasma infections combined with health education should be considered.

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.