Performance of IgG avidity in an area endemic for schistosomiasis in Egypt.

We assessed the performance of IgG avidity in the diagnosis of acute, chronic and recent (reinfection) on top of chronic schistosomal infections in patients treated with praziquantel. Immunoglobulin levels were studied in 111 patients with Schistosoma mansoni infection and 28 partially cured patients (not responding to the first dose of praziquantel treatment and almost cured after a second one). Before treatment all patients with schistosomiasis had elevated IgG levels, 75% of them also had increased IgM levels. Avidity index was high among all age groups. The increased IgM/IgG ratio and avidity index among children with schistosomiasis before treatment support the idea of reinfection. Treatment had no significant effect on the studied parameters. We conclude that unlike IgM and IgG antibody levels, IgG avidity test cannot be used to distinguish between recent and chronic infections.