The importance of detecting circulating Toxoplasma antigens in human cases

This work was performed on 100 suspected toxoplasmosis cases including 75 females with complicated obstetric histories, 15 children presented with hydrocephalus, retino-chorditis and lymphadenitis and 10 children suffering from leukaemia. Also 40 age-matched controls were included in this study. Serum samples from all patients and controls were examined to detect anti-Toxoplasma IgG and IgM using indirect ELISA. Antiserum against Toxoplasma avirulent strain was prepared in New-Zealand white rabbit, then it was used after purification for detecting circulating Toxoplasma antigens in the sera of these studied groups using a double antibody sanwich ELISA technique. Positive anti-Toxoplasms IgG was detected in 45% of the female group while 19% were IgM positive. According to IgM/IgG ratio, 9 cases were considered as acutely infected-females and 25 as chronically infected ones. The mean optical density of both IgG and IgM among acutely and chronically infected females were found significantly higher than of the control groups. Ten non-leukaemic children were IgG and IgM positive cases and were considered as acutely infected patients. On the other hand, all children with leukaemia were negative for anti-Toxoplasma IgG and IgM. Eleven out of 19 acutely infected cases (58%) had positive Toxoplasma antigens, whereas, only one case (4%) with chronic infection had positive antigen level. The mean optical density of circulating antigen level was significantly higher among acutely infected females and children than chronically infected and control groups. No antigen level difference was found between chronically infected patients and control groups. Six children from leukaemic group (60%) had positive circulating Toxoplasma antigen levels with significantly higher mean optical density than control groups (P < 0.001). As a conclusion the results demonstrate that the detection of circulating antigens can aid in the diagnosis of infection by T. gondii in humans, specially in immuno-compromised patients whose serologic response can be impaired.