Resistance in cattle to Fasciola hepatica induced by gamma-ray attenuated larvae: results from a controlled field trial.

A significant resistance to natural infection in the field was obtained in calves inoculated with metacercariae of Fasciola hepatica attenuated at a gamma-irradiation level of 3 Krad. The mean fluke burden of vaccinated calves was 29 per cent of that of the controls. The resistance was reflected not only in reduced parasite burdens and low faecal egg counts, but also in the stability of gamma-glutamyltranspeptidase levels of the vaccinated calves compared with non-vaccinated controls. The gamma-ray dose of 3 Krad did not prevent a small proportion of the irradiated larvae reaching and maturing in the bile ducts.