Giardia lamblia (formerly also Lamblia intestinalis and also known as Giardia duodenalis) is a flagellated protozoan parasite that infects the gastrointestinal tract of humans. Infection causes giardiasis, a type of gastroenteritis that manifests itself with severe diarrhea and abdominal cramps. Other symptoms can include bloating, gas, fatigue, and weight loss. These 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. Filter use or boiling is recommended for purifying 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 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.

References

• Hetsko ML, McCaffery JM, Svard SG, Meng TC, Que X, Gillin FD. Cellular and transcriptional changes during excystation of Giardia lamblia in vitro. Exp. Parasitol. 1998;88(3):172-83.
• Svard SG, Meng TC, Hetsko ML, McCaffery JM, Gillin FD. Differentiation-driven surface antigen variation in the ancient eukaryote. Molec. Microbiol. 1998;30:979-89.
• Tovar J, León-Avila G, Sánchez LB, Sutak R, Tachezy J, Van Der Giezen M, Hernández M, Müller M, Lucocq JM. Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation. Nature 2003;426:172-176

External links

• The original version of this article was taken from a public domain source at http://www.nigms.nih.gov/news/releases/giardia.html
• Washington State Department of Health fact sheet on Giardia.