Effects of anticoagulants on the dye test for toxoplasmosis

Requirement for calcium ions in antibody-dependent complement-mediated cytolysis of Toxoplasma gondii

The mechanism of antibody-dependent complement-mediated cytolysis of Toxoplasma organisms was studied by using a selective chelating agent for Ca++, ethyleneglycol-bis (beta-aminoethyl ether)-N,N-tetraacetic acid (EGTA). Toxoplasma organisms were lysed by treatment with human serum containing anti-Toxoplasma antibodies and with fresh human-plasma at 37 degrees C for 1 h. The reaction was prevented by heat treatment of the fresh plasma at 56 degrees C for 30 min, confirming that the cytolysis of Toxoplasma organisms had been mediated by an activation of complement. The lytic reaction was completely inhibited by an addition of EGTA at final concentrations of more than 2.5 mM. Addition of Ca++ cleared the inhibitory effect of EGTA on the reaction. These results demonstrate that the antibody-dependent complement-mediated cytolysis of Toxoplasma organisms requires the presence of Ca++, indicating that the reaction is mediated by an activation of the classical complement pathway.

Estimations of the incidences of toxoplasma infections among pregnant women from different areas in Norway

2342 male military recruits from different parts of Norway were selected for serological screening with the dye test or the IgG-indirect fluorescent antibody test. The highest frequency of toxoplasma antibodies was observed in the south-western areas (27%), whereas the prevalence was found to be as low as 2% in the northermost areas of the country. On the basis of the prevalence values obtained in the different counties, the incidence rates for acquired infections in the pregnant population have been calculated. The annual incidence in Norway was estimated to be 4 0/00 and the incidence of congenital toxoplasmosis would be maximally 2 0/00 (or about 110 cases/year).