Responses of Fasciola hepatica infected sheep to various infection levels

The response to Fasciola hepatica was studied in sheep infected with 5, 30, 150 metacercariae. The animals were necropsied 12 weeks post-infection (p- i) for counting and measuring flukes. Cellular and humoral responses were d etected by peripheral eosinophil count, peripheral blood lymphocyte prolife ration with excretory-secretory products (FhESP) and ELISA. All sheep were infected at necropsy except one sheep which was infected with 5 metacercari ae. Mean parasitic intensities were 40%, 44% and 27% of the infection dose in sheep infected with 5, 30, 150 metacercariae respectively. FhESP-specifi c lymphocyte responses of the 3 infected groups were significantly enhanced in weeks 3 and 4 p-i (p < 0.05). The kinetics of the specific humoral resp onse were similar for the 3 infected groups but the antibody level was sign ificantly lower in animals infected with 5 metacercariae than in the 2 othe r infected groups from week 5 p-i to week 12 p-i (p < 0.05). Peripheral eos inophil count was significantly enhanced (p < 0.05) in infected groups. The numbers of peripheral eosinophils were significantly different between the 3 infected groups in week 3, 4 and 6 p-i and were related to infection lev el. These results confirm that sheep are highly susceptible to F. hepatica infection, even when infection pressure is very low. Peripheral eosinophili a was dependent of the infection level. The immune response was similar in sheep infected with various numbers of flukes.