Evaluation of specific immunoglobulin G avidity enzyme linked immunosorbent assay (IgG avidity ELISA) in diagnosis of early and chronic Schistosomiasis mansoni.

This work was performed to study variations of Schistosoma specific immunoglobulins between early and chronic schistosomiasis mansoni in both children and adults. A modified enzyme linked immunosorbent assay (ELISA), based on dissociation of antigen antibody complexes with 8 mol/L urea (8 M urea) solution, was used to measure levels of low avidity immunoglobulin G antibodies (IgG Abs) against Schistosoma mansoni soluble egg antigen (SEA). The study included eighty (80) patients with active mansonian schistosomiasis. They were classified according to age, history, clinical symptomatology and examination and direct parasitological methods of diagnosis into early and chronically infected children and adults. Sera of all patients were subjected to: ELISA measuring Schistosoma specific IgM and IgG., immunoglobulin G (IgG) avidity ELISA and indirect haemagglutination test (IHA). Schistosoma specific IgG avidity ELISA detected higher levels of both urea IgG inhibition percentage and low avidity IgG Abs in early cases of schistosomiasis than chronic ones in both children and adults. Levels of urea IgG inhibition percentage were higher in children than adults. Schistosoma specific IgM/IgG ratio was more than one (> 1) in early cases in both children and adults and less than one (< 1) in chronic cases in children and 70% of adults. IHA titres were statistically higher in chronic cases than early ones in children only. So, it can be concluded that IgG avidity ELISA is a valuable method that helps to differentiate early from chronic schistosomiasis mansoni infection in both children and adults.