Abstract

The present study attempted to demonstrate an acquired immunity against Clonorchis sinensis in albino rat. Three separate experiments were carried out to determine acquired resistance developed by stimulating procedure followed by challenging infection with metacercariae. Acquired resistance was evaluated by the rate of recovery or the average number of flukes recovered from the liver of challenged albino rats, compared with the controls. In drder to demonstrate the rate of recovery of the fluke, three experimental groups of rats were challenged with 50 metacercariae per rat- 7,15 and 30 days after single injection of worm extract. The recovery rate was ranged from 33.2% to 38.0% in experimental group and their control group harbored from 37.8% to 42.6%. No significant difference was found on statistical analysis. In experimental groups received two immunizing injections with worm extract followed by challenging infection of metacercariae. Statistically significant difference was recovered between experimentals and controls. It was noted that reduction of the recovery rate was prominent in Group 5 and 6, which were challenged 15 and 30 days after two stimulating injections. From the third experiment which was consisted of single immunizing infection with 20 metacercariae followed by challenging infection with 30 metacercariae, no significant reduction was found between experimental rats and their controls. The number of recovered worms ranged from 16.2 to 18.5 worms in experimental group, while that of control group ranged from 18.9 to 19.8 worms. The evidence of delayed hypersensitivity reaction was observed in the groups with acquired immunity developed rats, by histopathological study of host hepatic tissue.