Validity of igG avidity enzyme linked immunosorbent assay and polymerase chain reaction for the determinatipn of toxoplasma infections during pregnancy

ABSTRACT

Accurate diagnosis of maternal toxoplasmosis can enhance the success of medical treatment and prevent congenital transmission. The current diagnostic methods have significant limits and they poorly differentiate between acute and chronic infections. The present study was conducted to diagnose acquired Toxoplasma infection in pregnant women by detecting both the low avidity-IgG using enzyme linked immunosorbent assay [ELISA] and the specific DNA by polymerase chain reaction technique [PCR]. The study was performed on 104 pregnant women at different gestational ages. The serum sample from each case was primarily screened for IgG by ELISA, and then positive samples were examined for IgM and estimation of IgG avidity ELISA. The PCR technique was performed on blood samples from twenty selected cases, ten of whom were positive for both IgG and IgM antibodies and the other ten were positive for IgG only. Out of 104 pregnant females screened by IgG ELISA 48 cases were positive. Twenty seven of these cases were positive for IgG only and 21 had both IgG and IgM antibodies. Of the 27 IgG positive cases 24 showed high IgG avidity while the remaining three showed inconclusive avidity. Of the 21 cases positive for both IgG and IgM antibodies 16 patients showed low avidity while five cases only showed high avidity. PCR was done for ten cases positive for both IgG and IgM antibodies and ten positive for IgG only. It proved positive in only four often cases who were positive for both IgG and IgM and had low IgG avidity. This study highlights the value of IgG avidity ELISA as a single serum sample test indicating the presence of infection and differentiating between acute and chronic infections. It is recommended as a routine test for every pregnant woman. A positive PCR can act as an excellent indicator of recent infection, but its disadvantage lies in the fact that negative results cannot exclude acute infection. In addition it is an expensive technique. Thus IgG avidity ELISA can be considered as a more appropriate technique