Serodiagnosis of human opisthorchiasis using cocktail and electroeluted Bithynia snail antigens

Cocktail and electroeluted antigens from Bithynia goniomphalos, the snail intermediate host of Opisthorchis viverrini, were extracted and purified. The performance of these two antigens in the antibody detection of human opisthorchiasis was evaluated by indirect ELISA. Serum samples from people whose stool was either: (i). positive for Opisthorchis eggs (n=61); or (ii). positive for at least one of 19 other species of parasite (n=125); or (iii). clear of parasites (n=30) were tested. The sensitivity, specificity, positive predictive value and negative predictive value of ELISA using cocktail antigen were 88.5, 88, 78.2 and 94%, respectively; those of ELISA using eluted antigen (53 kDa) were 91.8, 98.4, 96.5 and 96.1%, respectively. Cross-reaction with the eluted antigen was seen in only one of four cases of hymenolepiasis and only one of 10 cases of strongyloidiasis. The kappa coefficients for ELISA in relation to stool examination were 0.84 (cocktail antigen) and 0.87 (eluted antigen). This study showed that Bithynia snail antigen could be used to replace worm antigen in the antibody detection of human O. viverrini infection.