The role of Avidity Test in the Diagnosis of Acute and Chronic Infection with Toxoplasma Gondii

Abstract

Background: Toxoplasma gondii has a worldwide distribution and is one of the most prevalent infectious agents in humans. However, primary infection during pregnancy

constitutes a great diagnostic challenge, by predisposing the offspring to the risk of  congenital toxoplasmosis.

Objective: To detect the Toxoplasma IgG antibodies developed at the early stage of infection in pregnant women. Methods: 80  pregnant women, who were in the 2nd to 4th month of their pregnancy, enrolled in this study. Anti-toxoplasma IgG, IgM and IgG avidity were evaluated by ELISA method. Results:The patients were categorized into three groups as follows: Group A, 2 cases; IgG+,IgM+, 2.5%; group B, 3 cases; IgM+, IgG-, 3.75%; and group C, 75 cases; IgM -, IgG +,75(93.75%). 2.5% of the pregnant women had positive IgG and IgM among which 6.25% had low avidity which revealed an active infection in the pregnant women. In the current study, 75(93.75) of pregnant women had positive IgG and negative IgM, all of which had high avidity, which is an indication that in our population the level of toxoplasmosis infection is high and most women have had contacts with this parasite before pregnancy. Conclusion: In this study, the low avidity test was 6.25% showing that the occurrence of toxoplasmosis infection is still a serious issue. Observation of 75(93.75%) high avidity among group B suggests that either IgM has a high half-life or there is a false positive IgM as a result of rheumatologic disorders. Therefore, avidity test is important to differentiate between past and acute infection and because the titer of IgG remain high for long time.

Keywords: Toxoplasmosis, Avidity test, acute and chronic infection.