Tissue responses in experimental Schistosomiasis japonica in the pig: A histopathologic study of different stages of single low- or high-dose infections

The tissue responses of pigs exposed to either 100 or 2,000 Schistosoma jap onicum cercariae were examined at 4, 11, 17, and 24 weeks postinfection (PI ) to explore the pig as an animal model for pathologic aspects of human sch istosomiasis japonica. Egg granulomas were present in the liver, intestine, and occasionally in the lungs from 11 weeks PI. There were also many free eggs and early exudative reactions to eggs in the intestine. At 11 weeks PI , pigs in the higher dose group showed marked periportal and septal fibrosi s with minimal parenchymal destruction. Thereafter lesions regressed sponta neously as the pigs underwent a self-cure. The lower dose group showed only mild lesions throughout the study. The degree of hepatic fibrosis was corr elated with the density of eggs and granulomas in liver tissue. The results indicate that the pig would be particularly useful for studies of the deve lopment and resolution of schistosomal hepatic fibrosis, and also for inves tigations of the mechanisms behind the self-cure phenomenon.