Pathogenesis

The cyst form is responsible for infection because, unlike the trophozoite, it is resistant to stomach acid. Two trophozoites emerge from each cyst when it reaches the small intestine. Some of these trophozoites attach to the epithelium by their adhesive disc, while others move freely in the intestinal mucus using their

24.7 Protozoan Diseases of the Lower Alimentary System

Figure 24.22 Scanning Electron Micrograph of Giardia lamblia Trophozoites in Human Intestine

flagella. Some may even migrate up the bile duct to the gallbladder and cause crampy pain or jaundice. The protozoa do not destroy the host epithelium, but in severe infestations they may entirely cover the epithelial surface. They interfere with the ability of the intestine to absorb nutrients and secrete digestive enzymes. The result is malnutrition, bulky feces containing fat, and excessive intestinal gas from bacterial digestion of unabsorbed food material. Some of the intestinal impairment is probably a side effect of the host immune system attacking the parasites.

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