Iso-electricfocusing of Bithynia snail antigens for IgG- and IgG(1-4)-ELISA detection of human opisthorchiasis

Diagnosis of opisthorchiasis is confirmed by the presence of characteristic eggs and worms. However, misdiagnosis may occur in light infections, and also due to the morphological similarity of opisthorchid eggs to other species. A finding of specific immune mediators can help confirm infection. This study used indirect ELISA to detect total IgG and IgG(1-4) with selected antigens of Bithynia siamensis goniomphalos extract, which were derived by liquid-phase iso-electricfocusing (IFE). Antigens (Iso-AgF) from 20 IEF fractionated fractions were selected based on a high ELISA-OD ratio between pooled-positive and pooled-negative sera. Iso-AgF 7, 7, 6, 2, and 10 resulted in high OD-ratio to total IgG, IgG1, 2, 3, and 4, respectively. A full-scale ELISA was conducted with sera from 50 opisthorchiasis cases, 196 from other parasitic-disease cases, and 35 healthy controls. Iso-AgF7 to IgG1 showed the best result, with sensitivity, specificity, positive and negative predictive value of 100, 96, 86, and 100%, respectively, at a cut-off 0.221. Low cross-reactivity to IgG1 was found in one case each of gnathostomiasis, trichinellosis, toxocariasis, angiostrongyliasis, bancroftian filariasis, enterobiasis, neurocysticercosis, and taeniasis. Thus, Iso-AgF7 to IgG1 was a good candidate antigen to be developed for detection of antibodies against Opisthorchis viverrini.