- Infection with Giardia is through ingestion of the environmentally-resistant cyst form of the organism. Once inside the small intestine the cysts release the motile trophozoite form which is kite-shaped, bi-nucleated, and flagellated. The trophozoites feed and asexually reproduce within the small intestine and some reform into cysts as they pass through the remaining alimentary tract and are shed in the feces. Consequently, spread of giardia is through fecal-oral transmission and usually occurs through ingestion of contaminated water.
- Giardia trophozoites are not invasive but do adhere and can coat the small intestine epithelium. In doing so, they can significantly interfere with GI lipid absorption.
- Infection with Giardia is often subclinical but can result in an intense infectious diarrhea. Because lipid absorption is disrupted, a lipid-rich malodorous and frothy steatorrhea often manifests. Importantly, these organisms are not invasive; therefore, blood and inflammatory cells are never present in the feces.