Giardia lamblia

Giardia lamblia is a parasite which exists in 2 forms, a trophozoite and cyst, trophozoites live in the small intestine of the host and cysts are passed in the faeces of an infected host. The next host is infected when it ingests cysts in food or water contaminated with faeces.

Giardiasis is diagnosed by finding cysts or trophozoites in the faeces, both life cycle stages have a characteristic appearance. The trophozoites have a distinct "tear drop" shape and two nuclei.

Giardia lamblia does not invade the tissues of the small intestine however, the trophozoites do adhere to the lining of the small intestine. The symptoms associated with giardiasis range from none to severe diarrhoea.

Most infections result from ingestion of water or food contaminated with human sewage. However, in some countries the use of human faecal material as a fertiliser is also an important source of infection. In developed countries potable water can be contaminated with small amounts of sewage, especially when septic systems are built too close to wells.