RESUMO
A monoclonal antibody (MoAb) 1C12 that reacts with a 66 kDa surface tegumental (ST) antigen of adult worms of Fasciola gigantica was used to detect circulating antigen in sera of experimentally and naturally infected cattle. A combination of rabbit anti ST-antigens and MoAb 1C12 were used to capture and detect the circulating antigen in sandwich ELISA. The dilutions of 1:1,000 of rabbit anti ST-antigens and 1:100 for MoAb 1C12 were used to reduce cross-reactivity with other trematodes' antigens. The circulating antigen of F. gigantica was demonstrated in sera of all experimentally infected animals as early as the first week after the infection, and it remained detectable until the experiment was terminated at week 32 after the infection. Of the 97 serum samples from naturally infected cattle, the sensitivity of 86.6% was observed when the cut-off point was calculated from 32 serum specimens from uninfected control calves. The sensitivity increased to 100% when the commercial fetal calf and trematode-free baby calves sera were used for calculation of the control cut-off point. Based on these results, the combination of rabbit anti ST-antigens and MoAb 1C12 sandwich ELISA appeared to be sensitive, specific, and applicable in the immunodiagnosis of fasciolosis in cattle for epidemiological study and monitoring of chemotherapeutic efficacy.