A laboratory and clinical study of the mechanism of mother-to-child infection of Toxoplasma

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ObjectivesCongenital Toxoplasma infection in the fetus frequently results in debilitating disease in the newborn. To better evaluate the period of maternal infection, we examined avidity of maternal anti-Toxoplasma IgG.Study MethodsOne hundred and forty-four anti-Toxoplasma IgM-positive pregnant women were prospectively tested for IgG avidity for Toxoplasma to determine the period of Toxoplasma infection. We adapted this serologic technique to a commercial ELISA kit "Toxo IgG EIA Seiken" (Denka Seiken, Japan) using 8 M urea as a dissociating agent.Results・The mean specific IgM of the pregnant women was 2.65 +/-1.36.・Of the 144 pregnant women 123 (85.4%) had high avidity results (indicative of previous infection), 9(6.3%) had low avidity results (indicative of recent infection), and 12 (8.3%) had borderline results.・All of 72 neonates had no physical and neurological abnormality. Three were LFD, 8 were HFD, and 55 were AFD.・neonates ; 72 cases without anomaly・positive anti-Toxoplasma IgM ; 0/66・anti-Toxoplasma IgM : 0.24±0.12 (m±SD)・abnormal pathological findings of placenta : 0/29・positive PCR in placenta and cord bloods : 0/16・Abnormal funduscopic findings : 0/36・Abnormal CT scan findings : 0/29・Half-life of anti-Toxoplasma IgG : 31.4±4.5 days (23 non-infected offspring)ConclusionsAs a high IgG avidity can differentiate previously inflected women from IgM-positive pregnant women, measurement of the avidity will avoid unnecessary amniocentesis, medication, and artificial abortion.