Diagnosis of opisthorchiasis by enzyme-linked immunosorbent assay using partially purified antigens.

Opisthorchis viverrini antigens were partially purified from adult worms collected from liver and extrahepatic biliary system of infected hamsters. Tegument fraction was obtained by chemical extraction, whereas other fractions were purified by Sephadex G-200 gel filtration chromatography. Five fractions of O. viverrini antigens were obtained, namely tegument extract, somatic extract, fraction 1 (P1), fraction 2 (P2) and fraction 3 (P3), respectively. The enzyme-linked immunosorbent assay technique was used to compare the reactivity of the five partially purified antigens. The sensitivity and specificity of all five antigens were compared by testing against the sera of 78 O. viverrini-infected individuals from O. viverrini endemic areas and 70 individuals from non-endemic areas infected with hookworm, Trichuris and Ascaris including 49 individuals with negative stool examination. The assays performed with tegument extract, somatic extract and P1 fraction were found to have 100% sensitivity, whereas the sensitivities of those with P2 and P3 were 96.1% and 83.3%, respectively. The tegument extract had the highest specificity as demonstrated by the lowest cross-reactivity with other parasites. Our results indicated that surface tegument is the most suitable antigen for use in immunological diagnosis of opisthorchiasis.