Giardia
Encyclopedia
Giardia is a genus
of anaerobic
flagellate
d protozoa
n parasites of the phylum Metamonad
a in the supergroup "Excavata" (named for the excavated groove on one side of the cell body) that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis
, commonly known as Beaver fever. Their life cycle alternates between an actively swimming trophozoite and an infective, resistant cyst
. The genus was named after French zoologist Alfred Mathieu Giard
.
s, Giardia have two nuclei
, each with four associated flagella, and lack both mitochondria
and a Golgi apparatus
. However they are now known to possess mitochondrial relics, called mitosome
s. These are not used in ATP
synthesis the way mitochondria are, but are involved in the maturation of iron-sulfur protein
s. The synapomorphies
of genus Giardia include cells with duplicate organelles, absence of cytostome
s, and ventral adhesive disc.
s of infected humans or other animals. Individuals become infected
through ingesting or coming into contact with contaminated food, soil, or water. The Giardia parasite originates from contaminated items and surfaces that have been tainted by the feces of an infected animal.
The symptoms of Giardia, which may begin to appear 1–2 weeks after infection, include diarrhea
, excess gas, stomach or abdominal cramps, upset stomach, and nausea. Resulting dehydration and nutritional loss may need immediate treatment. The typical infection within an individual can be slight, resolve without treatment, and last between 2–6 weeks. Medication containing tinidazole
or metronidazole
decreases symptoms and time to resolution.
. Currently, five to six morphologically distinct species are recognised. 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. Other described, (but not certainly valid) species include:
Genetic and biochemical studies have revealed the heterogeneity of Giardia lamblia
, which contains probably at least eight lineages or cryptic species.
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.
A second isolate (the B assemblage) from humans has been sequenced along with a species from a pig (the E assemblage). 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of anaerobic
Anaerobic organism
An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present...
flagellate
Flagellate
Flagellates are organisms with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants...
d protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
n parasites of the phylum Metamonad
Metamonad
The metamonads are a large group of flagellate protozoa. Their composition is not entirely settled, but they include the retortamonads, diplomonads, and possibly the parabasalids and oxymonads as well...
a in the supergroup "Excavata" (named for the excavated groove on one side of the cell body) that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis
Giardiasis
Giardiasis or beaver fever in humans is a diarrheal infection of the small intestine by a single-celled organism Giardia lamblia. Giardiasis occurs worldwide with a prevalence of 20–30% in developing countries. In the U.S., 20,000 cases are reported to the CDC annually, but the true annual...
, commonly known as Beaver fever. Their life cycle alternates between an actively swimming trophozoite and an infective, resistant cyst
Microbial cyst
A microbial cyst is a resting or dormant stage of a microorganism, usually a bacterium or a protist, that helps the organism to survive in unfavorable environmental conditions. It can be thought of as a state of suspended animation in which the metabolic processes of the cell are slowed down and...
. The genus was named after French zoologist Alfred Mathieu Giard
Alfred Mathieu Giard
Alfred Mathieu Giard was a French zoologist born in Valenciennes on August 8, 1846. He was a professor at the Sorbonne, at École centrale de Lille and served as director of the marine laboratory in Wimereux ....
.
Characteristics
Like other diplomonadDiplomonad
The diplomonads are a group of flagellates, most of which are parasitic. They include most notably Giardia lamblia, which causes giardiasis in humans...
s, Giardia have two nuclei
Cell nucleus
In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. It contains most of the cell's genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones, to form chromosomes. The genes within these...
, each with four associated flagella, and lack both mitochondria
Mitochondrion
In cell biology, a mitochondrion is a membrane-enclosed organelle found in most eukaryotic cells. These organelles range from 0.5 to 1.0 micrometers in diameter...
and a Golgi apparatus
Golgi apparatus
The Golgi apparatus is an organelle found in most eukaryotic cells. It was identified in 1898 by the Italian physician Camillo Golgi, after whom the Golgi apparatus is named....
. However they are now known to possess mitochondrial relics, called mitosome
Mitosome
A mitosome is an organelle found in some unicellular eukaryotic organisms. The mitosome has only recently been found and named, and its function has not yet been well characterized. It was termed a 'crypton' by one group, but that name is no longer in use....
s. These are not used in ATP
Adenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
synthesis the way mitochondria are, but are involved in the maturation of iron-sulfur protein
Iron-sulfur protein
Iron-sulfur proteins are proteins characterized by the presence of iron-sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states...
s. The synapomorphies
Synapomorphy
In cladistics, a synapomorphy or synapomorphic character is a trait that is shared by two or more taxa and their most recent common ancestor, whose ancestor in turn does not possess the trait. A synapomorphy is thus an apomorphy visible in multiple taxa, where the trait in question originates in...
of genus Giardia include cells with duplicate organelles, absence of cytostome
Cytostome
A cytostome or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacuoles. Only certain groups of protozoa, such as the ciliates and excavates, have cytostomes. Such...
s, and ventral adhesive disc.
Infection and symptoms
Giardia lives inside the intestineIntestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
s of infected humans or other animals. Individuals become infected
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
through ingesting or coming into contact with contaminated food, soil, or water. The Giardia parasite originates from contaminated items and surfaces that have been tainted by the feces of an infected animal.
The symptoms of Giardia, which may begin to appear 1–2 weeks after infection, include diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
, excess gas, stomach or abdominal cramps, upset stomach, and nausea. Resulting dehydration and nutritional loss may need immediate treatment. The typical infection within an individual can be slight, resolve without treatment, and last between 2–6 weeks. Medication containing tinidazole
Tinidazole
Tinidazole is an anti-parasitic drug used against protozoan infections. It is widely known throughout Europe and the developing world as treatment for a variety of amoebic and parasitic infections...
or metronidazole
Metronidazole
Metronidazole is a nitroimidazole antibiotic medication used particularly for anaerobic bacteria and protozoa. Metronidazole is an antibiotic, amebicide, and antiprotozoal....
decreases symptoms and time to resolution.
Prevention
Person-to-person transmission accounts for a majority of Giardia infections and is usually associated with poor hygiene and sanitation. Water-borne transmission is associated with the ingestion of contaminated water. In the U.S. outbreaks typically occur in small water systems using inadequately treated surface water. Venereal transmission happens through fecal-oral contamination. Additionally, diaper changing and inadequate hand washing are risk factors for transmission from infected children. Lastly, food-borne epidemics of Giardia have developed through the contamination of food by infected food-handlers.Systematics
About 40 species have been described from different animals, but many of them are probably synonymsSynonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
. Currently, five to six morphologically distinct species are recognised. Giardia lamblia
Giardia lamblia
Giardia lamblia is a flagellated protozoan parasite that colonizes 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...
(=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
Vole
A vole is a small rodent resembling a mouse but with a stouter body, a shorter hairy tail, a slightly rounder head, smaller ears and eyes, and differently formed molars . There are approximately 155 species of voles. They are sometimes known as meadow mice or field mice in North America...
s. Other described, (but not certainly valid) species include:
- 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
Genetic and biochemical studies have revealed the heterogeneity of Giardia lamblia
Giardia lamblia
Giardia lamblia is a flagellated protozoan parasite that colonizes 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...
, which contains probably at least eight lineages or cryptic species.
Genome
A Giardia isolate (WB) was the first diplomonadDiplomonad
The diplomonads are a group of flagellates, most of which are parasitic. They include most notably Giardia lamblia, which causes giardiasis in humans...
to have its genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
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.
A second isolate (the B assemblage) from humans has been sequenced along with a species from a pig (the E assemblage). 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.
External links
- Giardiasis - Centers for Disease Control and PreventionCenters for Disease Control and PreventionThe Centers for Disease Control and Prevention are a United States federal agency under the Department of Health and Human Services headquartered in Druid Hills, unincorporated DeKalb County, Georgia, in Greater Atlanta...