The Mongolian gerbil (Meriones unguiculatus) as an experimental host for Entamoeba histolytica

Experimentally induced cecal and hepatic amebiasis was studied in the Mongolian gerbil (Meriones unguiculatus). Axenically cultivated Entamoeba histolytica trophozoites were inoculated into the cecum or the liver after laparotomy. Cecal infections were characterized by intense inflammation and distortion of the tissue. The intensity of the infection, measured by a standard method of scoring, was consistently high from 10 to 30 days postinoculation (p.i.). In tissue sections, disruption of the interglandular epithelium and presence of amebic ulcers and of large numbers of trophozoites were most noticeable 10 days p.i. In older infections there was cecal hypertrophy and crypt hyperplasia but only few amebae were seen. Amebic liver abscesses were well tolerated by gerbils and no mortality occurred. Growth of liver abscesses increased exponentially as the duration of the infection progressed from 5 to 30 days p.i. Liver abscesses were always confined to the inoculated liver lobe, and metastases did not occur. Early liver granulomas were discrete with well-defined walls. The abscesses had a fibrous wall and amebae were seen at their inner aspect. Older liver granulomas were coalesced, forming a single cavitary abscess with intense cellular infiltrate. Gerbils of all ages tested were equally susceptible to liver infections although larger abscesses were obtained in younger adult animals (60-80 days old). The Mongolian gerbil is proposed as a suitable animal model for experimental amebiasis because both the intestinal and hepatic aspects of the disease can be studied in it.