[Toxoplasmosis in pregnancy: new diagnostic techniques]

The diagnosis of primoinfection by Toxoplasma gondii in immunocompetent patients is not always easy because detectable levels of IgM are found in serum for months or even years.

We studied the prevalence of T. gondii antibodies in pregnant women and the usefulness of several commercial IgM and IgA detection systems as well as IgG avidity for the diagnosis of primoinfection by T. gondii. We also developed an IgA detection system in our laboratory and studied antigenic determiners recognized by various immunoglobulins by means of Western blot patterns.

The prevalence of antibodies in our environment is 56.70% and the incidence of primoinfection in pregnant women is 0.056%. In cases of primoinfection by T. gondii demonstrated by antibody seroconversion, we obtain positive results with all the systems tested. However, when seroconversion does not occur, we continue to get positive results in many cases with some of the technique tested. Nevertheless, there is a higher degree of correlation between the study of IgG avidity and IgA detection and seroconversion. With the Western blot technique, we can see that each type of immunoglobulin recognizes a different antigenic pattern, with antigen 31 kD being recognized by three types of immunoglobulins.

In spite of the high incidence of antibodies for Toxoplasma gondii in our medium, the incidence of primoinfection during pregnancy is low. As regards the evaluation of the different serological tests, except for seroconversion, none of the serological methods that we tested can independently diagnose primoinfection by T. gondii, even though IgG avidity studies and IgA produce the best results.