Detection of excretory-secretory circulating antigens in sheep infected with Fasciola hepatica and with Schistosoma mansoni and F. hepatica.

Two groups of sheep were exposed to Fasciola hepatica and Schistosoma mansoni/F. hepatica infections, respectively, to determine the time of appearance of F. hepatica circulating excretory-secretory (FhES) antigens. Five sheep were infected orally with 400 F. hepatica metacercariae. Five additional sheep were infected first percutaneously with 5000 S. mansoni cercariae, and 10 weeks later orally with 400 F. hepatica metacercariae. Antigen detection was performed in the two groups by a double antibody microELISA. In the group infected with F. hepatica, circulating FhES antigens were detected in all five animals. In the group infected first with S. mansoni none of the sera had positive optical density values for FhES antigens throughout the 10 week period following infection. After F. hepatica challenge, FhES antigens were detected in all animals. Thus, sheep infected with S. mansoni did not develop detectable F. hepatica circulating antigens during the 10 week period following Schistosoma infection. Anti-FhES antibodies were detected by FAST-ELISA, and all animals infected with F. hepatica were positive. In the group infected with S. mansoni, cross-reactive antibodies to F. hepatica were detected by 4-6 weeks post infection. All sheep with double infections showed high antibody levels by 2 weeks after infection with F. hepatica.