Typhlitis due to Balantidium coli in captive lowland gorillas. Typhlitis caused by Balantidium coli and requiring surgical resection occurred in three captive lowland gorillas over a 30-month period. Not one of the other gorillas in the colony or their keepers was ill. B. coli is distributed widely geographically and widely among mammals. Asymptomatic commensalism predominates, but invasion of the colonic mucosa can produce diarrhea and dysentery and set the stage for local or systemic spread. 