Comparative studies on animal models for Opisthorchis viverrini infection: host interaction through susceptibility and pathology.

Syrian hamsters and gerbils are animal models for Opisthorchis viverrini infection. In both models, the parasites develop into adults with different pathologies of the hepatobiliary system. However, no comparative pathological studies have yet been completed. We therefore investigated host interaction through the susceptibility and pathological changes of Syrian hamsters and gerbils infected with 50 O. viverrini metacercariae for 30, 60, and 90 days post-infection. Animals were sacrificed at each time point for comparative study. Susceptibility and infectivity were investigated through worm burden. Parasite morphology and reproductive organs were stained with carmine and observed under light microscopy. Reproductive organs and eggs per worm were counted to confirm worm maturity. Bile acid components of both animal groups were analyzed by thin-layer chromatography. The results showed that infection in gerbils was of greater severity than in Syrian hamsters by observation of bile obstruction, enlargement of the gallbladder and common bile duct, and generation of fibrosis and cirrhosis. The worm burden of infected gerbils was lower than that observed in Syrian hamsters. Infectivity in both Syrian hamsters and gerbils was 100% with infection by 50 metacercariae; whereas with 10 metacercariae, the infectivity in gerbils was zero to very low, but still 100% in Syrian hamsters. The largest body size of worms, and the largest ovary and testes areas, was correlated with eggs per gram of feces and eggs per worm. The bile acid components cholic acid and chenodeoxycholic acid were undetectable in gerbils. The present study suggests that although Syrian hamsters, usually the host selection for an animal model, are susceptible to O. viverrini infection, infected gerbils produce worms that mature more rapidly, have larger body sizes, and more fully developed reproductive organs; this may be caused by the difference in bile acid components.

Opisthorchis viverrini infection causes liver and biliary cirrhosis in gerbils.

Opisthorchis viverrini infection causes many hepatobiliary diseases, including cholangiocarcinoma. Hence, the study of O. viverrini infection in humans is subject to ethical limitations, so an animal model, the Syrian hamster, is often used. O. viverrini can develop into the adult stage not only in Syrian hamsters but also in other animals, including gerbils, but until now, there has been no report on pathology and susceptibility in gerbils. The present study revealed the pathology of O. viverrini infection in gerbils through gross appearance, histopathology, and worm recovery at various time points. Gerbils were infected with 50 O. viverrini metacercariae and then sacrificed at the time of observation. The gross appearance of the liver showed micronodules at the liver surface, suggesting liver and biliary cirrhosis. Light microscopic observation was correlated to the gross appearance with cholecystitis, fatty liver changes, fibrous septa, and generalized cirrhosis. The range of worm burden fluctuated from 1 to 25 worms with large body size, which was correlated with pathology. These novel findings indicate that O. viverrini infection can cause liver and biliary cirrhosis in gerbils, depending on the worm burden, worm size, and habitat.