Stock Photo - GIARDIA LAMBLIA Giardia lamblia trophozoite, colorized SEM. Giardia lamblia also named Giardia intestinalis is a flagellate protozoa, strict anaerobe, parasite of the intestine in mankind and numerous mammals. It transmits giardiasis. Giardia lamblia Giardia Hexamitidae Diplomonadida Mastigophora Sarcomastigophora Protozoan Protista. This scanning electron micrograph SEM revealed some of the external ultrastructural details displayed by a flagellated Giardia lamblia protozoan parasite. G. lamblia is the organism responsible for causing the diarrheal disease giardiasis. Once an animal or person has been infected with this protozoan, the parasite lives in the intestine, and is passed in the stool. Because the parasite is protected by an outer shell, it can survive outside the body, and in the environment for long periods of time. Cysts are resistant forms and are responsible for transmission of giardiasis. Both cysts and trophozoites can be found in the feces diagnostic stages. The cysts are hardy and can survive several months in cold water. Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal_oral route hands or fomites. In the small intestine, excystation releases trophozoites each cyst produces two trophozoites. Trophozoites multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel where they can be free or attached to the mucosa by a ventral sucking disk. Encystation occurs as the parasites transit toward the colon. The cyst is the stage found most commonly in non_diarrheal feces. Because the cysts are infectious when passed in the stool or shortly afterward, person_to_person transmission is possible. While animals are infected with Giardia, their importance as a reservoir is unclear.