Lucy V. Reardon

The Presence of Endamoeba histolytica in the Liver of Guinea Pigs with Experimental Intestinal Amebiasis.

Within the last 4 years, the guinea pig has been found to be a satisfactory experimental host for Endamoeba histolytica (Carrera and Faust, 1949; Taylor, Greenberg, Highman, and Coatney, 1950). This finding has greatly facilitated studies on the pathogenicity and chemotherapy of amebiasis (Taylor, Greenberg, and Josephson, 1952; Taylor and Greenberg, 1952). The lesions produced by E. histolytica in the cecum and colon of the guinea pig are often very severe. However, incidental examination of the liver has shown no macroscopic lesions, and microscopic study of smears of fresh liver tissue has failed to reveal the presence of amebas even in guinea pigs that were killed in the agonal stages of amebic dysentery. Because of the great importance of the question of whether E. histolytica may be frequently transported to the liver from intestinal lesions, it was decided to obtain more precise information on this point. Slices of liver, approximately 1 by 1 by 0.5 cm. in size, from intracecally infected animals were inoculated into culture medium in order to detect the parasite. The cultures were seeded with organism t, incubated at 37? C. and examined for as much as 144 hours for growth of amebas. In addition, through the courtesy of Dr. Benjamin Highman (Laboratory of Pathology, National Institute of Arthritis and Metabolic Diseases), sections of the liver from some of the animals were examined histopathologically for evidence of damage. This preliminary report presents the data thus far obtained. The data summarized in Table 1 show that the livers of 15 of the 20 guinea pigs of this experimental series were found infected with Endamoeba histolytica.2 Seventy cultures, or 18.6 percent of 377 tubes inoculated, were found positive for amebas. In many cases the amebas were found only after incubation for 96 or 144 hours, and in some cases only in transfers from the original cultures. Cultures were reported negative only after examination several times between 72 and 144 hours. The time elapsed between the experimental inoculation and post-mortem examination of the guinea pigs is shown in Table 1. The earliest examination was performed 7 days after injection; in this case the liver was found infected, by culture, and the intestinal lesions were graded as most severe. As yet, however, the data are too meager to indicate a relationship between the severity of the intestinal lesions and the occurrence of the parasite in the liver. In a series of cases not tabulated here, there was no parasitism of the liver when the intestinal infection was detectable only by finding parasites within the lumen without demonstrable lesions in the wall. Data from the table show that the left lobe of the liver was found in-