Entamoeba histolytica: liver invasion and abscess production by intraperitoneal inoculation of trophozoites in hamsters, Mesocricetus auratus.

Intraperitoneal inoculation of axenically cultured Entamoeba histolytica trophozoites constitutes an easy to perform, highly reproducible procedure for inducing amebic liver abscesses in hamsters. Efficiency in abscess production (95% of infected animals after 1 week) was similar to data reported using direct intrahepatic or intraportal inoculation. The morphological sequence of infection shows that amebas in the peritoneal cavity initially produce a large exudate constituted mainly of acute inflammatory cells. These cells form a rim of polymorphonuclear leukocytes surrounding the amebas, which adhere to the trophozoite and can sometimes be observed polarized to one end of the parasite, suggesting capping of surface receptors. Early stages are also characterized by the production of distant inflammatory reactions in the hepatic portal spaces. At 6 h postintraperitoneal inoculation, larger foci of inflammatory reactions surrounding amebas are developed in the peritoneum, extending to and damaging the liver surface membranes as well as the serosa of other internal organs. Thereafter, tissue damage progresses deeper into the liver parenchyma, and a few days later, coalescing granulomas and large necrotic areas are observed in the liver tissue. Based on the present morphological time-sequence study, we suggest that inflammatory cells associated with E. histolytica trophozoites play an important role in commencing the damage of liver sheaths and producing the subsequent parenchymal lesions. The simplicity and reliability of this model are important factors to consider when large numbers of experimentally induced amebic liver abscesses are needed.