Habitat of Giardia in the Intestine.

Abstract

Authorities on intestinal protozoa (Hegner, 1 Wenyon, 2 Lynch 3 ) state that Giardia lives in the upper part of the small intestine, mainly in the duodenum rather than in the cecum which is a common habitat for Trichomonas and Chilomastix. Hegner 4 has described Giardia canis as the species present in the dog, but has not recorded the level of the intestine in which this organism has been found. In connection with our Tulane Strain A of Endamoeba histolytica in dogs we have encountered Giardia canis as a contamination. In maintaining the ameba in vivo by continuously subinoculating one dog from another per rectum (Faust), we have had an opportunity to study in life and at autopsy dogs which have received the Giardia as an experimental infection. These observations we have compared with data obtained from naturally infected dogs.

In the majority of our cases harboring a natural Giardia infection the primary seat of the organism is in the cecum and appendix; frequently it is also in the colon and the rectum; occasionally it is found in the distal 10 cm. of the ileum; it has never been seen by us in the higher levels of the small intestine. In experimental infections of our dogs, previously found by repeated fecal examination to be negative for intestinal protozoa, we have encountered a somewhat different situation. The active Giardia trophozoites were introduced by rectal tube into the upper levels of the large bowel and usually expelled there. In some cases the tube passed the ileo-cecal valve and the inoculum was discharged anterior to the valve. In nearly 50 cases available for analysis an infection of 100% has been obtained. In most of the animals the active Giardias were consistently present in the feces from the second day; in 4 instances they were recorded as early as 24 hours after inoculation.