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==Overview==
==Overview==
'''''Giardia lamblia''''' (synonymous with '''''Lamblia intestinalis''''' and '''''Giardia duodenalis''''') is a [[flagellate]]d [[protozoa]]n [[parasite]] that is responsible for the development of giardiasis.


'''''Giardia lamblia''''' (synonymous with '''''Lamblia intestinalis''''' and '''''Giardia duodenalis''''') is a [[flagellate]]d [[protozoa]]n [[parasite]] that colonises and reproduces in the small intestine, causing [[giardiasis]].  The giardia parasite attaches to the [[epithelium]] by a [[ventral]] adhesive disc, and reproduces via [[binary fission]]<ref>Oxford textbook of Medicine, Fourth Edition, Volume 1. ''Oxford University Press'' pp759-760</ref>. Giardiasis does not [[disseminate]] [[haematogenously]], nor does it spread to other parts of the gastro-intestinal tract, but remains confined to the [[lumen]] of the small intestine<ref>Harrison's Internal Medicine, Harrison's Online Chapter 199 ''Protozoal intestinal infections and trochomoniasis''</ref>.  Giardia [[trophozoite|trophozoites]] absorb their nutrients from the lumen of the small intestine, and are [[anaerobe|anaerobes]].
==Higher Order Classification==
 
''Eukaryota'', ''Diplomonadida'' group, ''Diplomonadida'', ''Hexamitidae'', ''Giardiinae'', ''Giardia'', ''G. lamblia''
==Natural Reservoir==
==Natural Reservoir==
*Giardia affects humans and animals, such as cats, dogs, cows, beavers, deer, and sheep.
*Giardia affects humans and animals, such as cats, dogs, cows, beavers, deer, and sheep.


==Microbiological Characteristicsc==
*''Giardia lamblia'' is a flagellated, microaerophilic parasite.
*The trophozoite form of G. lamblia is pear-shaped and has a unique morphology that includes two identical nuclei, a ventral disc for adhesion to the host intestine, and flagella.
==Genome==
*''G. lamblia'' genome consists of 1.2 million base pairs (average GC content: 46%).<ref name="pmid1840670">{{cite journal| author=Le Blancq SM, Kase RS, Van der Ploeg LH| title=Analysis of a Giardia lamblia rRNA encoding telomere with [TAGGG]n as the telomere repeat. | journal=Nucleic Acids Res | year= 1991 | volume= 19 | issue= 20 | pages= 5790 | pmid=1840670 | doi= | pmc=PMC328996 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=1840670  }} </ref>
*The genome pairs are distributed across five linear chromosomes.<ref name="pmid1840670">{{cite journal| author=Le Blancq SM, Kase RS, Van der Ploeg LH| title=Analysis of a Giardia lamblia rRNA encoding telomere with [TAGGG]n as the telomere repeat. | journal=Nucleic Acids Res | year= 1991 | volume= 19 | issue= 20 | pages= 5790 | pmid=1840670 | doi= | pmc=PMC328996 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=1840670  }} </ref>
*Similar to other eukaryotes, each chromosome is flanked by the telomere sequence (5’TAGGG3’).<ref name="pmid1840670">{{cite journal| author=Le Blancq SM, Kase RS, Van der Ploeg LH| title=Analysis of a Giardia lamblia rRNA encoding telomere with [TAGGG]n as the telomere repeat. | journal=Nucleic Acids Res | year= 1991 | volume= 19 | issue= 20 | pages= 5790 | pmid=1840670 | doi= | pmc=PMC328996 | url=http://www.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pubmed&tool=sumsearch.org/cite&retmode=ref&cmd=prlinks&id=1840670  }} </ref>
==Life cycle==
==Life cycle==
[[Image:Giardia lamblia life cycle.jpg|right|thumb|Parasite life cycle.]]
[[Image:Giardia lamblia life cycle.jpg|right|thumb|Parasite life cycle.]]
''Giardia'' belongs among the [[diplomonad]]s.
''Giardia'' belongs among the [[diplomonad]]s.
===Non-infective Cyst===
*The life cycle begins with a noninfective cyst being excreted with faeces of an infected individual. Once out in the environment, the cyst becomes infective.
*A distinguishing characteristic of the cyst is 4 nuclei and a retracted cytoplasm.
===Trophozoite===
*Once ingested by a host, the trophozoite emerges to an active state of feeding and motility. 
*After the feeding stage, the trophozoite undergoes asexual replication through longitudinal binary fission.
*The resulting trophozoites and cysts then pass through the digestive system in the feces.
*While the trophozoites may be found in the feces, only the cysts are capable of surviving outside of the host.
*Distinguishing features of the trophozoites are large karyosomes and lack of peripheral chromatin, giving the two nuclei a halo appearance.


Giardia infection can occur through ingestion of dormant cysts in contaminated water, or by the faecal-oral route (through poor hygiene practices).  The Giardia cyst can survive for weeks to months in cold water<ref name="Huang">{{cite journal |author=Huang DB, White AC |title=An updated review on Cryptosporidium and Giardia |journal=Gastroenterol. Clin. North Am. |volume=35 |issue=2 |pages=291-314, viii |year=2006 |pmid=16880067 |doi=10.1016/j.gtc.2006.03.006}}</ref>, and therefore can be present in contaminated wells and water systems, and even clean-looking mountain streams, as well as city reservoirs, as the Giardia cysts are resistant to conventional water treatment methods, such as chlorination and ozonolysis.<ref name="Huang"> </ref>  [[Zoonotic]] transmission is also possible, and therefore Giardia infection is a concern for people camping in the wilderness or swimming in contaminated streams or [[lake]]s, especially the artificial lakes formed by [[beaver]] [[dam]]s (hence the popular name for giardiasis, "Beaver Fever").
As well as water-borne sources, faecal-oral transmission can also occur, for example in day care centres, where children may have poorer hygiene practices.  Those who work with children are also at risk of being infected, as are family members of infected individuals.  Not all Giardia infections are symptomatic, so some people can unknowingly serve as carriers of the parasite.
The life cycle begins with a noninfective cyst being excreted with faeces of an infected individual.  Once out in the environment, the cyst becomes infective.  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. 
After the feeding stage, the trophozoite undergoes asexual replication through longitudinal binary fission.  The resulting trophozoites and cysts then pass through the digestive system in the faeces.  While the trophozoites may be found in the faeces, only the cysts are capable of surviving outside of the host.
Distinguishing features of the trophozoites are large karyosomes and lack of peripheral chromatin, giving the two nuclei a halo appearance.  Cysts are distinguished by a retracted cytoplasm.  This protozoa lacks [[mitochondria]], although the discovery of the presence of mitochodrial remnant [[organelles]] in one recent study "indicate that Giardia is not primitively amitochondrial and that it has retained a functional organelle derived from the original mitochondrial endosymbiont"<ref>{{cite journal |author=Tovar J, León-Avila G, Sánchez LB, ''et al'' |title=Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation |journal=Nature |volume=426 |issue=6963 |pages=172-6 |year=2003 |pmid=14614504 |doi=10.1038/nature01945}}</ref>
==Manifestation of Infection==
Nomenclature for Giardia species are difficult, as humans and other animals appear to have morphologically identical parasites.
Colonisation of the gut results in inflammation and villous atrophy, reducing the gut's absorptive capability.  In humans, infection is symptomatic only about 50% of the time, and protocol for treating asymptomatic individuals is controversial.<ref name="Huang"> </ref>  Symptoms of infection include (in order of frequency) diarrhea, malaise, excessive gas (often flatulence or a foul or sulphuric-tasting belch, which has been known to be so nauseating in taste that it can cause the infected person to vomit), [[steatorrhoea]] (pale, foul smelling, greasy stools), epigastric pain, bloating, nausea, diminished interest in food, possible (but rare) vomiting which is often violent, and weight loss.<ref name="Huang"> </ref> Pus, mucus and blood are not commonly present in the stool.  In healthy individuals, the condition is usually self-limiting, although the infection can be prolonged in patients who are immunocompromised, or who have decreased gastric acid secretion.<ref name="Huang"> </ref>  People with recurring Giardia infections, particularly those with a lack of IgA, may develop chronic disease.  [[Lactose intolerance|Lactase deficiency]] may develop in an infection with Giardia, however this usually does not persist for more than a few weeks, and a full recovery is the norm.
Cats can be cured easily, lambs usually simply 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 a high infection rate, as 30% of the population under one year old are known to be infected in kennels.  The infection is more prevalent in puppies than in adult dogs. This parasite is deadly for chinchillas, so extra care must be taken by providing them with safe water. Infected dogs can be isolated and treated, or the entire pack at a kennel can be treated together regardless.  Kennels should also be then cleaned with bleach or other cleaning disinfectants.  The grass areas used for exercise should be considered contaminated for at least one month after dogs show signs of infection, as cysts can survive in the environment for long periods of time.  Prevention can be achieved by quarantine of infected dogs for at least 20 days and careful management and maintenance of a clean water supply.
==Prevention and Treatment==
Treatment of drinking water for Giardia typically involves high efficiency filtration and/or chemical disinfection such as [[chlorination]] or [[ozone|ozonation]]. However, normal concentrations of chlorine and ozone used in mass water treatment are not adequate to kill the cysts. Scooping water from the top of a stream or river is <b>not</b> an effective way to avoid Giardia.  Filtering (<1[[Micrometre|ųm]] pore) or boiling is recommended for [[water purification|purification]] of [[drinking water]] in wilderness conditions. 
A Giardia lamblia infection in humans is diagnosed with an antigen test or, if that is unavailable, an ova and parasite examination of stool. Multiple stool examinations are recommended, since the cysts and trophozoites are not shed consistently.
Human infection is conventionally treated with metronidazole, tinidazole or nitazoxonide.  Although Metronidazole is the current first-line therapy, it is [[mutagenic]] in bacteria and [[carcinogenic]] in mice, so should be avoided during pregnancy.<ref name="Huang"> </ref>  One of the most common alternative treatments is [[berberine sulfate]] (found in [[Oregon grape root]], [[goldenseal]], [[yellowroot]], and various other plants).  [[Berberine]] has been shown to have an [[antimicrobial]] and an [[antipyretic]] effect.  Berberine compounds cause [[uterine]] stimulation, and so should be avoided in pregnancy.  High doses of berberine can cause [[bradycardia]] and [[hypotension]]. <ref>UpToDate (Lexi-Comp, Inc.) retrieved 28 August 2007</ref>
{| class="wikitable"
|-
! Drug
! Treatment duration
! Possible Side Effects
|-
| Metronidazole
| 5-7 days
| Metallic taste; nausea; vomiting; dizziness; headache; [[disulfiram|disulfiram-like]] effect; [[neutropenia]]
|-
| Tinidazole
| Single dose
| Metallic taste; nausea; vomiting; belching; dizziness; headache; [[disulfiram|disulfiram-like]] effect
|-
| Nitazoxanide
| 3 days
| Abdominal pain; diarrhoea; vomiting; headache; yellow-green discolouration of urine
|}
Table adapted from Huang, White..<ref name="Huang"> </ref>
==Microscopy==
[[Image:giardia.jpg|right|thumb|400px|This picture shows multiple views of a single Giardia lamblia (intestinalis) cyst as imaged at different instrument settings by confocal microscopy.Bar = 10 micrometres.<br />(A) is the cyst imaged by transmission (differential interference contrast), only.<br />(B) is the cyst wall selectively imaged through use of fluorescent-labelled (TRITC) antibody that is cyst wall specific.</br>(C) is the cyst imaged through use of carboxy fluorescein diacetate, a viability stain.<br />(D) is a composite image of (B) and (C).<br />(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.
==Research==
Giardia alternates between two different forms &mdash; 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.<ref>{{cite journal |author=Hetsko ML, McCaffery JM, Svärd SG, Meng TC, Que X, Gillin FD |title=Cellular and transcriptional changes during excystation of Giardia lamblia ''in vitro'' |journal=Exp. Parasitol. |volume=88 |issue=3 |pages=172-83 |year=1998 |pmid=9562420 |doi=10.1006/expr.1998.4246}}</ref><ref>{{cite journal |author=Svärd SG, Meng TC, Hetsko ML, McCaffery JM, Gillin FD |title=Differentiation-associated surface antigen variation in the ancient eukaryote Giardia lamblia |journal=Mol. Microbiol. |volume=30 |issue=5 |pages=979-89 |year=1998 |pmid=9988475 |doi=}}</ref> They also uncovered several ways in which the parasite  evades the defences of the infected organism. One of these is by altering the [[protein]]s on its surface, which confounds the ability of the infected animal's [[immune system]] to detect and combat the parasite (called [[antigenic variation]]). Gillin's 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.


==History==
The [[trophozoite]] form of Giardia was first observed in 1681 by [[Antoni van Leeuwenhoek]] in his own diarrheal stools. In 1915, the parasite was named in honour of Professor A. Giard of Paris.  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.<ref>Ford, BJ [http://www.brianjford.com/Giardia-14-06.pdf The discovery of ''Giardia''] The Microscope 2005;53(4):148-153.</ref>
In 1998, there was a Giardia outbreak in Sydney, Australia that was found to be due to contamination of the water supply.  This was ameliorated with improved water treatment.
A similar outbreak took place in Oslo, Norway in October 2007. The outbreak was also found to be due to contamination of the water supply.
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==References==
==References==
{{Reflist|2}}
{{Reflist|2}}
==External links==
*[http://giardiadb.org/giardiadb/ GiardiaDB: The Giardia lamblia genome sequencing project]
*[http://www.doh.wa.gov/ehsphl/factsheet/giardia.htm Washington State Department of Health fact sheet on Giardia].
*[http://www.cdc.gov/ncidod/dpd/parasites/giardiasis/factsht_giardia.htm Center for Disease Control fact sheet on Giardia]
*[http://microbewiki.kenyon.edu/index.php/Giardia Giardia article at MicrobeWiki]
*[http://video.google.com/videoplay?docid=-965376292862019004&hl=en Video of Giardia Life Cycle]
*[http://www.yosemite.org/naturenotes/Giardia.htm Giardia and the Sierra Nevada]




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Giardia lamblia
Giardia cell, SEM
Giardia cell, SEM
Scientific classification
Kingdom: Protista
Phylum: Metamonada
Genus: Giardia
Species: G. lamblia
Binomial name
Giardia lamblia
(Kunstler, 1882)
This page is about microbiologic aspects of the organism(s).  For clinical aspects of the disease, see Giardiasis.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Giardia lamblia (synonymous with Lamblia intestinalis and Giardia duodenalis) is a flagellated protozoan parasite that is responsible for the development of giardiasis.

Higher Order Classification

Eukaryota, Diplomonadida group, Diplomonadida, Hexamitidae, Giardiinae, Giardia, G. lamblia

Natural Reservoir

  • Giardia affects humans and animals, such as cats, dogs, cows, beavers, deer, and sheep.

Microbiological Characteristicsc

  • Giardia lamblia is a flagellated, microaerophilic parasite.
  • The trophozoite form of G. lamblia is pear-shaped and has a unique morphology that includes two identical nuclei, a ventral disc for adhesion to the host intestine, and flagella.

Genome

  • G. lamblia genome consists of 1.2 million base pairs (average GC content: 46%).[1]
  • The genome pairs are distributed across five linear chromosomes.[1]
  • Similar to other eukaryotes, each chromosome is flanked by the telomere sequence (5’TAGGG3’).[1]

Life cycle

Parasite life cycle.

Giardia belongs among the diplomonads.

Non-infective Cyst

  • The life cycle begins with a noninfective cyst being excreted with faeces of an infected individual. Once out in the environment, the cyst becomes infective.
  • A distinguishing characteristic of the cyst is 4 nuclei and a retracted cytoplasm.

Trophozoite

  • Once ingested by a host, the trophozoite emerges to an active state of feeding and motility.
  • After the feeding stage, the trophozoite undergoes asexual replication through longitudinal binary fission.
  • The resulting trophozoites and cysts then pass through the digestive system in the feces.
  • While the trophozoites may be found in the feces, only the cysts are capable of surviving outside of the host.
  • Distinguishing features of the trophozoites are large karyosomes and lack of peripheral chromatin, giving the two nuclei a halo appearance.


References

  1. ↑ 1.0 1.1 1.2 Le Blancq SM, Kase RS, Van der Ploeg LH (1991). "Analysis of a Giardia lamblia rRNA encoding telomere with [TAGGG]n as the telomere repeat". Nucleic Acids Res. 19 (20): 5790. PMC 328996. PMID 1840670.
  2. ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 "Public Health Image Library (PHIL)".
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