Giardia lamblia

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Giardia lamblia (formerly also Lamblia intestinalis and also known as Giardia duodenalis and Giardia intestinalis) is a flagellated protozoan parasite that infects the gastrointestinal tract of humans. It is also one of the most common parasites infecting cats. Infection causes giardiasis, a type of gastroenteritis that manifests itself with severe diarrhea and abdominal cramps. Other symptoms can include bloating, flatulence, fatigue, nausea, vomiting and weight loss. In some patients, vomiting or nausea is the major symptom. The symptoms usually manifest themselves about seven to ten days after the organism is ingested. Giardia is a major cause of intestinal disease worldwide and the most frequent non-bacterial cause of diarrhea in North America. Nonetheless, the basic biology of this parasite is poorly understood.

Infection from giardia can occur from consuming contaminated food or water. It can also be transferred from animal or human feces. Not every person displays symptoms of infection, but they can still serve as a carrier of the disease. Giardia infection is a concern for people camping in the wilderness or swimming in contaminated streams or lakes, especially the artificial lakes formed by beaver dams (hence the popular name for giardiasis, "Beaver Fever"). Filter use or boiling is recommended for water purification of drinking water in wilderness conditions.

Giardia belongs among the diplomonads. It alternates between two different forms — a hardy, dormant cyst that contaminates water or food and an active, disease-causing form that emerges after the parasite is ingested. National Institute of General Medical Sciences grantee Dr. Frances Gillin of the University of California, San Diego and her colleagues cultivated the entire life cycle of this parasite in the lab and identified biochemical cues in the host's digestive system that trigger Giardia's life cycle transformations. They also uncovered several tricks the parasite uses to evade the defenses of the infected organism. One of Giardia's techniques is to alter the proteins on its surface, which confounds the ability of the infected animal's immune system to detect and combat the parasite. This work reveals why Giardia infections are extremely persistent and prone to recur. In addition, these insights into Giardia's biology and survival techniques may enable scientists to develop better strategies to understand, prevent, and treat Giardia infections.

The trophozoite form of Giardia was first observed in 1681 by Anton van Leeuwenhoek in his own diarrheal stools.

The picture at right shows multiple views of a single Giardia lamblia (intestinalis) cyst as imaged at different instrument settings by confocal microscopy. (A) is the cyst imaged by transmission (differential interference contrast), only. (B) is the cyst wall selectively imaged through use of fluorescent-labelled (TRITC) antibody that is cyst wall specific. (C) is the cyst imaged through use of carboxy fluorescein diacetate, a viability stain. (D) is a composite image of (B) and (C). (E) is a composite image of (A), (B), and (C). Bar = 10 micrometres. Under a normal compound light microscope, Giardia often looks like a "clown face," with two nuclei outlined by adhesive discs above dark median bodies that form the "mouth." Cysts have four nuclei.

Treatment of drinking water for Giardia typically involved some form of high efficiency filtration and/or chemical disinfection such as chlorination or ozonation. Treatment is necessary throughout North America. Scooping water from the top is not an effective way to avoid Giardia.

See also