Effect of Single Inocula of Endamoeba histolytica Trophozoites on Guinea Pigs. ∗ †

Abstract

Summary

Guinea pigs were inoculated intracecally with graded single doses of from 100 to 5,000,000 amebae. None of the animals that were given less than 1,000 amebae developed infection. The 50% infective dose under the experimental conditions was 10,000 amebae. The mean weight of the guinea pigs that later became infected was significantly smaller than that of those which resisted infection. Thirty-one out of 50 guinea pigs that received single inocula of from 5,000 to 5,000,000 amebae died as a result of the infection. The LD₅₀ under the experimental conditions was 63,000 amebae. Death occurred in all cases between 5 and 17 days after inoculation, on the average 9.3 days after inoculation, and the greatest number of guinea pigs died on the eighth day. In general, the size of the inoculum was found to have an inverse relationship to the average time between inoculation and death. Histopathologic studies confirmed necropsy examination. All animals found to be positive by gross examination and by direct smears of the cecal content were found to have typical amebic lesions, while in none of the controls and of those reported as negative were ulcers of any kind observed by histologic sections.