Loss of ability to kill Fasciola hepatica in sensitised rats

Abstract

RATS infected orally with metacercariae of the liver fluke Fasciola hepatica develop a partial resistance to oral challenge. This resistance occurs when the sensitising flukes have reached and are living in the bile ducts; resistance also develops if the sensitising infection is terminated by anthelmintics whilst the flukes are migrating through the liver parenchyma^1–3. Living adult flukes can be successfully transplanted into the peritoneal cavity of rats^4,5, but if the rats have been infected with F. hepatica metacercariae approximately 10 weeks previously, the flukes transferred into the peritoneal cavity will be killed^2,6. We report here that although a marked resistance to intraperitoneal challenge with adult flukes develops as early as 2 weeks after oral infection with normal metacercariae, rats which have been infected 12 months previously, and which still have living adult flukes present in their bile ducts have lost this immunity. If rats with long-standing fluke infections in their bile ducts are reinfected with metacercariae, however, the ability of the rats to kill the challenge flukes is restored.