In three experiments the character of the feces and the condition of the colon and cecum were observed in 34 young adult dogs that had been placed on either a normal or salmon diet and, after 2 weeks, either inoculated orally with cysts of Entamoeba histolytica or not inoculated.
During the 34 to 96 days of observation, most of the dogs lost weight, those on the salmon diet to a greater extent than the others. No signs of vitamin deficiencies were observed. Twelve dogs on normal diet passed normal stools and displayed no intestinal lesions not attributable to worms; one of nine inoculated with E. histolytica acquired infection.
After 5 to 29 days, among 22 dogs on salmon diet, 12 regularly passed blood and mucus in fluid, often dysenteric, stools. Five of these dogs had been inoculated with E. histolytica, seven had not. In two of the salmon-fed dogs the stools were consistently normal and the intestinal mucosa also appeared to be normal; in the others, the mucosa was in some degree hemorrhagic and friable, with masses of sloughed epithelial cells in the covering mucus. E. histolytica infection was demonstrated in 5 of 9 inoculated dogs, but pathological changes seen in the colon and cecum were essentially the same irrespective of amebic infection. Bloody stools and bowel lesions in some cases apparently were in part due to hookworms, and amebae might have contributed to some of the changes seen; in most instances, however, the salmon diet appeared to have provided the chief causative factor. Thus, the results from earlier studies of amebic colitis in salmon-fed dogs may require reinterpretation.
Present address: Department of Parasitology, University of Chile, Santiago.