The effect of route of infection on acquired resistance to Fasciola hepatica in the rat and sheep.

Rats and sheep were infected with Fasciola hepatica by subcutaneous, intramuscular or oral (intraruminal--sheep) inoculation with encysted metacercariae and the development of flukes from these primary infections assessed. Additional rats and sheep similarly infected were challenged with encysted metacercariae orally (rats), or intraruminally (sheep) to assess the level of acquired resistance generated by previous infection by each of the three routes of administration. In both rats and sheep 0--5 per cent, 0--5 per cent and 20--25 per cent of metacercariae given by the subcutaneous, intramuscular or oral (intraruminal--sheep) routes were recovered as flukes in the liver four and 12 weeks after infection of rats, or 17 weeks after infection of sheep. Primary infection of rats with F hepatica by each of the three routes generated strong protection against oral challenge whereas no protection was generated in sheep, irrespective of route of infection.