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{{short description|Genus of flagellate intestinal eukayotes parasitic in various vertebrate}}
{{About|the parasite|the disease|Giardiasis}}
{{Use dmy dates|date=July 2013}}
{{Taxobox
| image = Giardia lamblia SEM 8698 lores.jpg
| image_caption = ''Giardia'' [[trophozoite]], [[Scanning electron microscope|SEM]]
| domain = [[Eukaryota]]
| unranked_regnum = [[Excavata]]
| phylum = [[Metamonad]]a
| ordo = [[Diplomonad]]ida
| familia = [[Hexamitidae]]
| subfamilia = [[Giardiinae]]
| genus = '''''Giardia'''''
| genus_authority = Künstler, 1882<ref>{{cite journal|author=Künstler, J.|year=1882|title=Sur cinq protozoaires parasites nouveaux|journal=C. R. Acad. Sci. Paris|volume=95|pages=347–349|url=https://gallica.bnf.fr/ark:/12148/bpt6k30518/f347.item}}</ref>
| synonyms ={{Genus list
|Lamblia|R. Blanchard, 1888<ref>{{cite journal|author=Blanchard, R.|year=1888|title=Remarques sur le megastome intestinal|journal=Bull. Soc. Zool. Fr.|volume=30|pages=18–19|url=https://gallica.bnf.fr/ark:/12148/bpt6k5439498p/f43.item}}</ref>
}}
| subdivision_ranks = Species
| subdivision =
''[[Giardia agilis]]'' 
''[[Giardia ardeae]]'' 
''[[Giardia lamblia]]'' 
''[[Giardia microti]]'' 
''[[Giardia muris]]'' 
''[[Giardia psittaci]]''
}}

'''''Giardia''''' ({{IPAc-en|dʒ|iː|ˈ|ɑr|d|i|ə}} or {{IPAc-en|ˈ|dʒ|ɑr|d|i|ə}}) is a [[genus]] of [[Anaerobic organism|anaerobic]] [[flagellate]]d [[protozoa]]n [[Human parasite|parasite]]s of the phylum [[metamonada]] that colonise and reproduce in the small intestines of several [[vertebrates]], causing [[giardiasis]]. Their life cycle alternates between a swimming [[trophozoite]] and an infective, resistant [[Microbial cyst|cyst]]. ''Giardia'' were first described by the [[Netherlands|Dutch]] [[microscopist]] [[Antonie van Leeuwenhoek]] in 1681.<ref name="ErlandsenMeyer1984">{{cite book|author1=Stanley L. Erlandsen|author2=Ernest A. Meyer|title=Giardia and Giardiasis: Biology, Pathogenesis, and Epidemiology|url=https://books.google.com/books?id=F8IIzx8PaWAC&pg=PA131|date=1 March 1984|publisher=Springer|isbn=978-0-306-41539-5|pages=131–}}</ref> The genus is named after French [[zoologist]] [[Alfred Mathieu Giard]].<ref name=Adam01>{{cite journal |author=Adam RD |title=Biology of ''Giardia lamblia'' |journal=Clin. Microbiol. Rev. |volume=14 |issue=3 |pages=447–75 |date=July 2001 |pmid=11432808 |pmc=88984 |doi=10.1128/CMR.14.3.447-475.2001 }}</ref>

==Characteristics==
Like other [[diplomonad]]s, ''Giardia'' have two [[cell nucleus|nuclei]], each with four associated [[Flagellum|flagella]], and were thought to lack both [[mitochondrion|mitochondria]] and a [[Golgi apparatus]]. However they are now known to possess a complex endomembrane system as well as mitochondrial remnants, called [[mitosome]]s, through mitochondrial reduction.<ref>{{Cite journal|last1=Tovar|first1=Jorge|last2=León-Avila|first2=Gloria|last3=Sánchez|first3=Lidya|last4=Sutak|first4=Robert|last5=Tachezy|first5=Jan|last6=van der Giezen|first6=Mark|last7=Hernández|first7=Manuel|last8=Müller|first8=Miklós|last9=Lucocq|first9=John|date=2003|title=Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation|journal=Nature|volume=426|issue=6963|pages=172–176|doi=10.1038/nature01945|pmid=14614504|bibcode=2003Natur.426..172T|s2cid=4402808}}</ref>
<ref>{{cite journal |
author= Anna Karnkowska|
title= A Eukaryote without a Mitochondrial Organelle |
journal= Current Biology|
date= May 2016|
url=http://www.cell.com/current-biology/fulltext/S0960-9822(16)30263-9|display-authors=etal |doi=10.1016/j.cub.2016.03.053 |
pmid= 27185558 |volume=26 |
issue= 10 |pages=1274–1284|
doi-access= free }}
</ref>
<ref>{{cite journal |vauthors=Soltys BJ, Falah M, Gupta RS |title=Identification of endoplasmic reticulum in the primitive eukaryote ''Giardia lamblia'' using cryoelectron microscopy and antibody to Bip |journal=J. Cell Sci. |volume=109 |issue=Pt 7 |pages=1909–17 |date=July 1996 |doi=10.1242/jcs.109.7.1909 |pmid=8832413 |url=http://jcs.biologists.org/cgi/pmidlookup?view=long&pmid=8832413}}</ref><ref>{{cite journal |author1=Dolezal P |author2=Smíd O |author3=Rada P |display-authors=etal |title=Giardia mitosomes and trichomonad hydrogenosomes share a common mode of protein targeting |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=102 |issue=31 |pages=10924–9 |date=August 2005 |pmid=16040811 |pmc=1182405 |doi=10.1073/pnas.0500349102 |bibcode=2005PNAS..10210924D }}</ref> The mitosomes are not used in [[Adenosine triphosphate|ATP]] synthesis the way mitochondria are, but are involved in the maturation of [[iron-sulfur protein]]s.<ref name="Tovar2003">{{cite journal |vauthors=Tovar J, etal | year = 2003 | title = Mitochondrial remnant organelles of Giardia function in iron-sulphur protein maturation | journal = Nature | volume = 426 | issue = 6963 | pages = 172–6 | pmid = 14614504 | doi = 10.1038/nature01945 | bibcode = 2003Natur.426..172T | s2cid = 4402808 }}</ref> The [[synapomorphy|synapomorphies]] of genus ''Giardia'' include cells with duplicate organelles, absence of [[cytostome]]s, and ventral adhesive disc.<ref>{{cite web |last=Cepicka |first=Ivan |title=Fornicata |website=Tree of Life Web Project |date=September 2008 |url=http://tolweb.org/Fornicata/121182/2008.09.02}}</ref>

==Systematics==
About 40 species have been described from different animals, but many of them are probably [[Synonym (taxonomy)|synonyms]].<ref name="Meyer1979">{{cite journal |author1=Meyer E.A. |author2=Radulescu S. | year = 1979 | title = ''Giardia'' and Giardiasis | journal = Advances in Parasitology | volume = 17 | pages = 1–47 | pmid = 395833 | doi = 10.1016/S0065-308X(08)60548-5 | quote = no |isbn=9780120317172 }}</ref> Currently, five to six morphologically distinct species are recognised.<ref>{{cite book |first1=R.C. |last1=Brusca |first2=G.J. |last2=Brusca |title=Invertebrates |publisher=Sinauer Associates |edition=2nd |year=2003 |isbn=0878930973 }}</ref> ''[[Giardia lamblia]]'' (=''G. intestinalis'', =''G. duodenalis'') infect humans and other mammals, ''G. muris'' is found from other mammals, ''G. ardeae'' and ''G. psittaci'' from birds, ''G. agilis'' from amphibians and ''G. microti'' from [[vole]]s.<ref name=Adam01/> Other described (but not certainly valid), species include:<ref>{{cite web |title=Giardia Kunstler |date=September 2008 |work=Tree of Life Web Project |url=http://tolweb.org/Giardia/97370/2008.09.02}}</ref>
{{div col|colwidth=22em}}
*''Giardia beckeri''
*''Giardia beltrani''
*''Giardia botauri''
*''Giardia bovis''
*''Giardia bradypi''
*''Giardia canis''
*''Giardia caprae''
*''Giardia cati''
*''Giardia caviae''
*''Giardia chinchillae''
*''Giardia dasi''
*''Giardia equii''
*''Giardia floridae''
*''Giardia hegneri''
*''Giardia herodiadis''
*''Giardia hyderabadensis''
*''Giardia irarae''
*''Giardia marginalis''
*''Giardia melospizae''
*''Giardia nycticori''
*''Giardia ondatrae''
*''Giardia otomyis''
*''Giardia pitymysi''
*''Giardia pseudoardeae''
*''Giardia recurvirostrae''
*''Giardia sanguinis''
*''Giardia serpentis''
*''Giardia simoni''
*''Giardia sturnellae''
*''Giardia suricatae''
*''Giardia tucani''
*''Giardia varani ''
*''Giardia viscaciae''
*''Giardia wenyoni''
{{div col end}}
Many different species of ''Giardia'' exist, so to differentiate between species, very specific PCR (Polymerase Chain Reactions) have been developed to detect specific ''Giardia'' spp. Gene probe-based detection is also used to differentiate between species of ''Giardia''. A more common and less time-consuming means of identifying different species of ''Giardia'' includes microscopy and immunofluorescence techniques.<ref>{{harvnb|Mahbubani|1992}}</ref>

Genetic and biochemical studies have revealed the heterogeneity of ''[[Giardia lamblia]]'', which contains probably at least eight lineages or [[cryptic species]].<ref>{{cite journal |vauthors=Thompson RC, Monis PT |title=Variation in Giardia: implications for taxonomy and epidemiology |journal=[[Adv. Parasitol.]] |volume=58 |pages=69–137 |year=2004 |pmid=15603762 |doi=10.1016/S0065-308X(04)58002-8 |series=Advances in Parasitology |isbn=9780120317585 }}</ref>

==Genome==
A ''Giardia'' isolate (WB) was the first [[diplomonad]] to have its [[genome]] sequenced. Its 11.7 million [[basepair]] genome is compact in structure and content with simplified basic cellular machineries and metabolism. Currently the genomes of several other ''Giardia'' isolates and diplomonads (the fish pathogens ''Spironucleus vortens'' and ''S. salmonicida'') are being sequenced.<ref name= Anderssonetal>{{Cite book|author= Andersson, JO| year=2010 |chapter=The Genome of Giardia and Other Diplomonads |title=Anaerobic Parasitic Protozoa: Genomics and Molecular Biology | publisher=[[Caister Academic Press]] | isbn= 978-1-904455-61-5|display-authors=etal}}</ref>

A second isolate (the B assemblage) from humans has been sequenced along with a species from a pig (the E assemblage).<ref name="Jerlström-Hultqvist2010">{{cite journal |vauthors=Jerlström-Hultqvist J, Ankarklev J, Svärd SG |title=Is human giardiasis caused by two different Giardia species? |journal=Gut Microbes |volume=1 |issue=6 |pages=379–82 |year=2010 |pmid=21468219 |pmc=3056102 |doi=10.4161/gmic.1.6.13608 |url=http://www.landesbioscience.com/journals/gmic/abstract.php?id=13608}}</ref> There are ~5000 genes in the genome. The E assemblage is more closely related to the A assemblage than is the B. A number of chromosomal rearrangements are present.

==Infection==
[[File:Giardia-spp.--infected--gerbil-intestine.jpg|thumb|left|250px|An [[scanning electron micrograph|SEM micrograph]] of the [[small intestine]] of a [[gerbil]] infested with ''Giardia'' reveals a mucosa surface almost entirely obscured by attached [[trophozoites]]]]
{{Main|Giardiasis}}
''Giardia'' lives in the [[intestine]]s of infected humans or other animals, individuals of which become [[infection|infected]] by ingesting or coming into contact with contaminated foods, soil, or water tainted by the feces of an infected carrier.<ref>{{cite journal |author=Filice, F.P. |author-link=Francis P. Filice |title=Studies on the cytology and life history of a ''Giardia'' from the laboratory rat |journal=U. C. Publications in Zoology |volume=5sex7 |issue=2 |year=1952 |location=Berkeley CA |publisher=University of California Press}}</ref>

The symptoms of ''Giardia'', which may begin to appear 2 days after infection, include violent [[diarrhoea]], excess gas, stomach or abdominal cramps, upset stomach, and nausea. Resulting dehydration and nutritional loss may need immediate treatment. A typical infection can be slight, resolve without treatment, and last between 2–6 weeks, although it can sometimes last longer and/or be more severe. Coexistence with the parasite is possible (symptoms fade), but an infected individual can remain a carrier and transmit it to others. Medication containing [[tinidazole]] or [[metronidazole]] decreases symptoms and time to resolution. [[Albendazole]] is also used, and has an [[anthelmintic]] (anti-worm) property as well, ideal for certain compounded issues when a general vermicidal agent is preferred.
''Giardia'' causes a disease called [[giardiasis]], which causes the villi of the small intestine to atrophy and flatten, resulting in malabsorption in the intestine. Lactose intolerance can persist after the eradication of ''Giardia'' from the digestive tract.<ref>{{harvnb|LaCour|2003}}</ref>

==See also==
*[[List of parasites (human)]]

==References==
{{Reflist}}

==External links==
*{{cite web |title=Giardia |date=March 2011 |work=Parasites |publisher=[[Centers for Disease Control and Prevention]] |url=https://www.cdc.gov/parasites/giardia/ |ref={{harvid|CDC Giardia|2011}}}}
*{{cite journal |vauthors=Mahbubani MH, Bej AK, Perlin MH, Schaefer FW, Jakubowski W, Atlas RM |title=Differentiation of ''Giardia duodenalis'' from other Giardia spp. by using polymerase chain reaction and gene probes |journal=J. Clin. Microbiol. |volume=30 |issue=1 |pages=74–8 |date=January 1992 |doi=10.1128/JCM.30.1.74-78.1992 |pmid=1734070 |pmc=264999 |ref={{harvid|Mahbubani|1992}}}}
*{{cite web |last=LaCour |first=Michelle |title=Who Is Giardia? |date=2003 |work=GIARDIA |publisher=Stanford University |url=http://www.stanford.edu/group/parasites/ParaSites2003/Giardia/GIARDIA2.htm }}
*{{cite web |title=''Giardia'' |work=NCBI Taxonomy Browser |url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Info&id=5740 |id=5740}}

{{Excavata}}
{{Antonie van Leeuwenhoek}}
{{Taxonbar|from=Q1469628}}

[[Category:Metamonads]]
[[Category:Excavata genera]]
[[Category:1681 in science]]

[[pt:Giárdia]]

Giardia - Revision history

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