The effect of orally administered Entamoeba histolytica on Wistar and athymic (rnu rnu) rats observed during a 12-month period.

Groups of LacP (Wistar) and rnu rnu athymic rats were dosed orally with cultured trophozoites of 2 strains of Entamoeba histolytica, zymodeme II, and observed for up to 12 months. One group of Wistar rats remained infected but with no apparent disease for 6 months; faecal samples from another became negative after one week. All the athymic rats were still infected at 12 months and amoebae could be cultured from their stools. The effect of even long-term infection was usually only mild erosion of the caecal wall and only 2 rats developed typical chronic lesions and ulcers. Amoebae were isolated in culture from the apparently unaffected livers of 2 rats 12 months after infection.