Heterologous resistance to Fasciola hepatica conferred upon rats by passive transfer of serum from different breeds of sheep.

Two experiments compared the protection against oral challenge with 20 metacercariae of Fasciola hepatica conferred on rats by intraperitoneal injection of serum from three breeds of sheep infected with F. hepatica (Barbados Blackbelly, St. Croix, Florida Native). Experiment 1 used serum from sheep 5-6 months of age following two infections of 250 metacercariae each, while Experiment 2 utilized serum collected from the same sheep at 10-11 months of age following either a primary (first exposure) or challenge (after two previous exposures of 250 metacercariae each) infection with 500 metacercariae. Similar numbers of flukes were recovered from rats given either immune or nonimmune (control) serum from each breed of sheep in Experiment 1. In Experiment 2, rats given serum from infected St. Croix sheep had significantly fewer flukes than rats given either control or immune serum from Barbados Blackbelly or Florida Native sheep. There was no significant correlation of fluke counts between individual serum donors (sheep) and serum recipients (rats).