Sequential histopathology of cavitary liver abscess. Formation induced by axenically grown Entamoeba histolytica.

Multiple hamster liver passage of Entamoeba histolytica trophozoites with intervening recovery into axenic culture caused increased virulence as measured by increase in the size of the lesion produced. Lesions produced by amebae that had not been liver-passaged did not persist; however, multiply liver-passaged substrains produced large, fluid-filled abscesses one month to six weeks after inoculation. Six days after inoculation, lesions consisted of multiple granulomas, lymphocytes, and E histolytica trophozoites. Large, fluid-filled abscesses produced by liver-passaged substrains lacked the granulomatous appearance of the earlier lesions. The abscesses had a fibrous wall, with E histolytica trophozoites at the inner aspect. To our knowledge, the evolution of early granulomatous lesions into a cavitary abscess with features closely resembling those of human amebic abscess has not been reported previously in the experimental disease in the hamster.