Giardia lamblia

Giardia lamblia formerly also Lamblia intestinalis is a single-celled parasite that causes in humans infestation of gastrointestinal tract. In some cases the infection can lead to giardiasis that manifests itself with severe diarrhea and abdominal cramps.

It 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--including how it ravages the digestive tract--is poorly understood.

The organism exists in 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.

This picture 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 microns.

Recently, Giardia has been found to possess mitochondrial remnants known as 'mitosomes', which suggest that the condition of amitochondrialism is not primitive to eukaryotes but instead is a result of reductive evolution. The microaerophilic Giardia uses these mitosomes in the maturation of iron-sulfur proteins rather than in ATP synthesis as is the case in mitochondria-possessing eukaryotes.

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

The original version of this article was taken from a public domain source at http://www.nigms.nih.gov/news/releases/giardia.html

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