Humoral immune response and antigenemia in sheep experimentally infected with Schistosoma bovis. Cross-reactivity with Fasciola hepatica antigens

Circulating antigen level, IgG antibody response to worm antigens and to ex cretory/secretory products (ES), and specificity to Fasciola hepatica antig ens were determined in 6 Schistosoma bovis-infected sheep at weekly interva ls for 15 wk. A noninfected control group was included. An enzyme-linked im munosorbent assay (ELISA) sandwich and a double-antibody ELISA test was use d for antibody and antigen detection, respectively The infection induced an early and relatively low IgG response to adult worm extract. This response was significantly elevated by 3 wk postinfection (PI), reached its maximum level at 9 wk PI, and was followed by a subsequent decrease. The response to ES antigens was slightly higher than that to adult worms, although the r esponse started later, at 8 wk PI, and remained at its maximum level until 15 wk. A remarkable level of cross-reactivity was observed when adult F, he patica extract was used. However, a low degree of cross-reactivity was foun d with ES antigen. The ELISA for circulating antigens was performed at week ly intervals for 8 wk. Antigens were detected as early as the first week of infection, although differences were statistically significant from week 5 onward. The highest values were observed at 7 week PI.