IMMUNODIAGNOSTIC AND PATHOLOGICAL STUDIES ON EXPERIMENTAL FASCIOLIASIS IN RATS

The aim of this study was to establish an experimental model for fascioliasis in rats and to investigate the relationship between immunochemical changes in the blood and histopathological changes in the liver. Experimental infection with Fasciola sp. was established in Wistar rats of 5～9 weeks old. Direct evidence of infection was obtained from ovum positive stools, which appeared at 8 weeks after infection. The findings suggested that the parasite had matured to the adult stage in the liver. Additional evidence included an increase in the levels of GOT and GPT at 3 to 8 weeks and similar increases in LAP activity at 4 to 8 weeks after infection. The raised levels of GOT and GPT reflected liver parenchyma damage caused by fluke infestation and elavated LAP provided evidence of fluke migration into the bile ducts. Marked increases in specific antibody levels were detected by ELISA as early as 1 week after infection, and specific immunoprecipitation bands were detected 2 weeks after infection. Antibody levels reached maximum at 8～10 weeks after infection. These results suggest that the ELISA method could be especially useful in the early diagnosis of experimental fascioliasis in rats. Direct histopathological analysis of livers at intervals after infection demonstrated that : 1) metacercariae of Fasciola sp. mature to the adult stage in rats ; 2) invasion into the liver by the parasite occurred between 2 and 4 weeks ; 3) migration to the main bile duct occurred between 6 and 8 weeks ; 4) pathological changes in the liver caused by Fasciola sp. in this model were similar to those described for human fascioliasis. In conclusion, the present studies have established a useful model for experimental infection with Fasciola sp. in 5～9-week-old rats. In addition a specific micro ELISA for antibody to Fasciola sp. has been developed for the early diagnosis of fascioliasis. The process of invasion into the liver and migration into the biliary tract was monitored by the measurement of serum enzyme activities release from hepato-biliary foci