Hexamitiasis in a laboratory mouse colony

An acute fatal disease occurred in a mouse colony at the authors' institution. The disease caused 50% mortality among weanling mice, and was characterized clinically by depression, rough hair coat, and distention of the abdomen. The most prominent gross lesions were watery fluid and gas in the small intestine. Numerous organisms identified as Hexamita muris were seen in direct smears of the intestinal fluid. Microscopic and electron microscopic examination revealed the same organisms in the intestinal crypts, within the mucosal epithelium, and in the lamina propria. Treatment with dimetridazole controlled the clinical disease but did not eliminate the infection.