Screening for toxoplasmosis in pregnancy

Identification of potential serodiagnostic and subunit vaccine antigens by antibody profiling of toxoplasmosis cases in Turkey

Toxoplasmosis, caused by infection of the protozoan parasite Toxoplasma gondii, is associated with mild disease in healthy individuals, whereas individuals with depressed immunity may develop encephalitis, neurologic disorders, and other organ diseases. Women who develop acute toxoplasmosis during pregnancy are at risk of transmitting the infection to the fetus, which may lead to fetal damage. A diagnosis is usually confirmed by measuring IgG, or IgM where it is important to determine the onset of infection. A negative IgM result essentially excludes acute infection, whereas a positive IgM test is largely uninterpretable because IgM can persist for up to 18 months after infection. To identify antigens for improved diagnosis of acute infection, we probed protein microarrays displaying the polypeptide products of 1357 Toxoplasma exons with well-characterized sera from Turkey. The sera were classified according to conventional assays into (1) seronegative individuals with no history of T. gondii infection; (2) acute infections defined by clinical symptoms, high IgM titers, and low avidity IgG; (3) chronic/convalescent cases with high avidity IgG but persisting IgM; (iv) true chronic infections, defined by high avidity IgG and no IgM. We have identified 38 IgG target antigens and 108 IgM target antigens that can discriminate infected patients from healthy controls, one or more of which could form the basis of a 'tier-1' test to determine current or previous exposure. Of these, three IgG antigens and five IgM antigens have the potential to discriminate chronic/IgM persisting or true chronics from recent acutely infected patients (a 'tier-2' test). Our analysis of the antigens revealed several enriched features relative to the whole proteome, which include transmembrane domains, signal peptides, or predicted localization at the outer membrane. This is the first protein microarray survey of the antibody response to T. gondii, and will help in the development of improved serodiagnostics and vaccines.

SEROLOGICAL DIAGNOSIS OF TOXOPLASMA GONDII INFECTION IN VARIOUS PATIENT POPULATION IN THE ARMED FORCES

The study included 200 healthy age and sex matched controls (120 healthy volunteers and 80 healthy antenatal cases without any bad obstetric history) and 300 cases comprising patients with bad obstetric history (BOH) 80 cases, seizure or encephalitis 50 cases, cervical lymphadenopathy 30 cases, congenital deformity 30 cases, HIV infected 80 cases and patients on long term immunosuppression 30 cases. Anti-toxoplasma IgG & IgM were measured by ELISA and individuals found positive for anti Toxoplasma gondii IgM or with high titre of IgG were subjected to repeat testing after 3 weeks for rise in titre. True sero-prevalence of T gondii infection was found to be 19% and it increased with increasing age in the population. 2.33% patients were found to have acute toxoplasma infection. Statistical significance was seen only in patients with BOH and children born with congenital abnormality.

Gestational and neonatal toxoplasmosis: regional seroprevalence in the United Arab Emirates

Paired maternal/cord blood samples were tested for anti-Toxoplasma IgG or IgM antibodies using Biomerieux Micro-EIA2 IgG and IgM test kits. Of the 1503 women tested at the time of delivery, 344 (22.9%) were IgG seropositive. Three hundred and one maternal sera, including 265 that were IgG positive, were tested for IgM antibodies: 47 were found positive, indicating a gestational toxoplasmosis incidence of 31 per 1000 pregnancies over one year. All but one of the IgM positive maternal sera had tested IgG positive. Cord blood IgG seropositivity was similar to the maternal rate but 18 of the 301 babies had significant levels of anti-Toxoplasma IgM antibodies. As these 18 babies were all born to mothers also positive for IgM antibodies, the calculated rate of transplacental transmission was 38.3% with the estimated prevalence of congenital toxoplasmosis of 12 per 1000 live births. There was no statistically significant positive correlation between maternal seroprevalence and such well-known risk factors as consumption of raw meat and milk, or proximity of cats and other animals. One baby was born with the classical stigmata of congenital toxoplasmosis.

Screening for toxoplasmosis in pregnancy

Randomly collected sera from 386 pregnant women attending obstetric and gynecology clinics at Kind Khalid University Hospital, Riyadh, Saudi Arabia, were examined for toxoplasma antibodies by five serological methods, i.e. latex agglutination test (LAT), two indirect hemagglutination tests (IHAT) (Carter-Wallace, USA and Ismunit, Italy), enzyme immunoassay (EIA) and indirect fluorescent antibody test (IFAT). The percentage of sensitivity, specificity and coincidence value of these tests were compared with IFAT which was used as a reference test. For routine screening of toxoplasmosis, LAT has proved in this study to be the most suitable test. The LAT is cost effective and easy to perform. In this study of the three tests (IFAT, EIA, immunosorbent agglutination assay) to demonstrate specific IgM for toxoplasmosis, the EIA test proved to be the most satisfactory because of its 99% specificity. If EIA equipment is available, it can be used for routine screening (IgG) as well as IgM determination. The incidence of toxoplasmosis in pregnant women varied between 25.4% and 36.3% depending on the method used.

Congenital toxoplasmosis: epidemiologic features and control

Toxoplasmosis is caused by the parasite Toxoplasma gondii. It is acquired from undercooked meat or from food or fomites contaminated by cat feces. The disease can be transmitted to the fetus only during maternal parasitemia, which is associated with primary infection. Extrapolation from current data suggests that there are 140 to 1400 cases of congenital toxoplasmosis per year in Canada and that 70 to 280 of the infants are severely affected at birth; many of the others suffer sequelae later in life. Serologic diagnosis of primary infection in the mother is quite sensitive and specific. Diagnosis in the infant is more difficult and may take several months. Prenatal treatment of the woman and postnatal treatment of the infant are hampered by the lack of proven efficacy as well as ethical and compliance problems. Preventive serologic screening and prophylaxis have the same drawbacks. Educating young women to avoid infection is an inexpensive, low-risk intervention that would be the preferred preventive strategy if it could be shown to be effective. Immunization may prove to be the most cost-effective method of preventing congenital toxoplasmosis if a safe and effective vaccine is developed.

Congenital toxoplasmosis in England, Wales, and Northern Ireland: some epidemiological problems

It has been suggested that congenital toxoplasmosis could be prevented by antenatal serological screening, followed by treatment or by termination of pregnancy if infection occurs. The only study of the incidence of congenital toxoplasmosis in England, Wales, and Northern Ireland took place more than 10 years ago. To obtain more recent figures laboratory reports of cases occurring from 1975 to 1980 were analysed. A total of 91 cases were reported over the six years. By criteria established to classify these infections only 34 were congenital, 20 were acquired postnatally, and 37 were unclassifiable. The mean annual number of cases of congenital toxoplasmosis was considerably smaller than that found in other recent studies. The condition could be underdiagnosed or rates of placental transmission could be lower in Britain than in other countries. Variation in reporting criteria of the laboratories made the data difficult to interpret. Improved diagnosis of congenital toxoplasmosis would not only clarify the epidemiology but would also help clinicians in management of suspected cases. Further antenatal surveys are necessary to assess the role of screening in the prevention of congenital toxoplasmosis.