Detection of Toxoplasma gondii B1 gene in placenta does not prove congenital toxoplasmosis

BACKGROUND: Congenital toxoplasmosis is an important disease that occurs when pregnant women become infected with Toxoplasma gondii during pregnancy. The aim of this study was to investigate the presence of T. gondii B1 gene in placental tissues of IgM seronegative women. MATERIALS AND METHODS: In this research, chronic toxoplasmosis was identified through examination of blood samples in a group of pregnant women by anti-Toxoplasma IgG and IgM ELISA and nested-PCR techniques. IgG avidity test was used to estimate the onset of infection in some pregnant women with chronic infection. After delivery, some umbilical cord and neonatal blood were tested by anti-Toxoplasma IgM ELISA, and also the B1 gene of T. gondii was investigated in their placental tissue by nested-PCR. Some factors such as blood sampling time and some clinical symptoms experienced during pregnancy were recorded. RESULTS: One hundred and sixty seven out of 653 (25.6%) pregnant women were positive for anti-Toxoplasma IgG. Of them, 165 (98.8%) were negative for anti-T. gondii IgM. Six out of 10 (60%) placental tissues from IgG seropositive, IgM seronegative women were positive for T. gondii B1 gene, while anti-Toxoplasma IgM was negative in the umbilical cord and neonatal blood samples. The results of IgG avidity test showed low avidity in one and high avidity in two women's samples. The B1 gene was not found in the blood samples of any of the six mothers. The most symptoms experienced during pregnancy were headache and nausea. CONCLUSION: The detection of B1 gene in placental tissues of the healthy newborn infants reiterates that presence of T. gondii in the placenta does not always result in congenital toxoplasmosis.