Giardia lamblia
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 Giardia cell, SEM
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| Giardia lamblia (Kunstler, 1882) |
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 and causes giardiasis.
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[edit] Hosts
Giardia affects humans. It is also one of the most common parasites infecting cats. Mammalian hosts also include cows, beaver, deer, dogs and lambs.
[edit] Symptoms
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 ingestion. 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.
[edit] Life cycle
Giardia belongs among the diplomonads.
Infection from giardia can occur from consuming contaminated food or water; this includes clean-looking mountain streams. 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").
Giardia may be ingested at camping areas, day care centers, waterborne outbreaks, and is also highly infectious to other family members once one individual is infected. Other causes can be uncooked food, contaminated wells and failed municipal water systems.
The life cycle consists of a noninfected cyst being excreted out through feces of an infected individual. Once out in the environment, the cyst becomes infected. A distinguishing characteristic of the cyst is 4 nuclei and a retracted cytoplasm. Once ingested by a host, the trophozoite emerges to an active state of feeding and motility. It feeds on mucous inside the digestive tract and causes the host to have epigastric pain, excessive gas, and diarrhea with fat and mucous but no blood. This can last from 2 - 4 weeks but for a lactose intolerant individual, it can last up to six months.
After the feeding stage, the trophozoite undergoes asexual replication through longitudinal binary fission. The resulting trophoziotes and cysts then pass through the digestive system in the feces. Distinguishing features of the trophozoites are large karyosomes and lack of peripheral chromatin, giving the two nuclei a halo appearance. This is a primitive form of protozoa and also lacks mitochondria.
[edit] Manifestation in animals
Nomenclatures for Giardia species are hard since humans and other animals appear to have morphological identical parasites. Cats can be cured easily, lambs usually just lose weight, but in calves the parasites can be fatal and often are not responsive to antibiotics or electrolytes. Carriers among calves can also be asymptomatic. Dogs have the most problems since usually 30% of the population under one year old is infected in kennels. It is more a "puppy problem" than an adult one.
Treatment in kennels can be done by identifying the infected dogs and isolating them or just a mass treatment, followed by cleaning the entire kennel with bleach or other cleaning disinfectants. The grass area used for exercise should be considered contaminated for at least one month since cysts can survive in the environment for that long. Prevention can be achieved by quarantine for at least 20 days and managing the water supply to be clear of too many cysts.
[edit] Prophylaxis
Filter use or boiling is recommended for water purification of drinking water in wilderness conditions.
Treatment of drinking water for Giardia typically involves 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.
[edit] 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).
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.
[edit] Research
Giardia 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 laboratory, and identified biochemical cues in the host's digestive system which trigger Giardia's life cycle transformations. They also uncovered several ways in which the parasite evades the defenses of the infected organism. One of these is by altering the proteins on its surface, which confounds the ability of the infected animal's immune system to detect and combat the parasite. Gillin's work reveals why Giardia infections are extremely persistent and prone to recur. In addition, these insights into Giardias biology and survival techniques may enable scientists to develop better strategies to understand, prevent, and treat giardia infections.
[edit] History
The trophozoite form of Giardia was first observed in 1681 by Anton van Leeuwenhoek in his own diarrheal stools. His observations were recreated, using a single lensed microscope of the kind used by Leeuwenhoek, by British microbiologist Brian J. Ford who showed how clearly one could view Giardia through a primitive microscope.
[edit] 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.
- Ford, BJ The discovery of Giardia The Microscope 2005;53(4):148-153.
- 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
[edit] 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 (Broken Link)
- Washington State Department of Health fact sheet on Giardia.
- Center for Disease Control fact sheet on Giardia
