Giardia duodenalis

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Giardia duodenalis
Giardia lamblia SEM 8698 lores.jpg
Giardia lamblia cell, SEM
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Phylum: Metamonada
Order: Diplomonadida
Family: Hexamitidae
Genus: Giardia
Species:
G. duodenalis
Binomial name
Giardia duodenalis
Stiles, 1902
Synonyms
  • Cercomonas intestinalisLambl, 1859
  • Lamblia intestinalisBlanchard, 1888
  • Giardia lamblia(Lambl, 1859) Kofoid & Christiansen, 1915
  • Giardia intestinalisKulda & Nohýnková, 1995

Giardia duodenalis, also known as Giardia intestinalis and Giardia lamblia, is a flagellated parasitic protozoan microorganism of the genus Giardia that colonizes the small intestine, causing a diarrheal condition known as giardiasis. [1] [2] [3] The parasite attaches to the intestinal epithelium by an adhesive disc or sucker, and reproduces via binary fission. [4] Giardiasis does not spread to other parts of the gastrointestinal tract, but remains confined to the lumen of the small intestine. [5] The microorganism has an outer membrane that makes it possible to survive even when outside of its host, and which can render it tolerant to certain disinfectants. Giardia trophozoites are anaerobic, and absorb their nutrients from the intestinal lumen. If the organism is stained, its characteristic pattern resembles the familiar "smiley face" symbol. [6]

Contents

Chief pathways of human infection include ingestion of untreated drinking water (which is the most common method of transmission for this parasite), [3] food, soil contaminated with human feces, and sewage, a phenomenon particularly common in many developing countries. [7] [3] Contamination of natural waters also occurs in watersheds where intensive grazing occurs.

Giardia infections occur worldwide. It is the most commonly identified intestinal parasite among children in day-care centers, hikers, immunocompromised adults and their family members in the United States and Canada. About 20,000 cases per year in the United States are reported. [8]

Life cycle

Lifecycle of Giardia lamblia Giardia life cycle en.svg
Lifecycle of Giardia lamblia

G. duodenalis takes on two morphologically distinct forms during its lifecycle. The replicative form is a motile, pear-shaped, flagellated cell that survives only in the small intestine of the host, called a trophozoite. [9] Trophozoites swim through the intestinal mucus until they eventually adhere to the intestinal epithelium. [10] [9] Adhered trophozoites then divide by binary fission, forming either more trophozoites or the nonreplicative cyst stage. [9] Cysts and trophozoites pass through the host's large intestine and are shed in the feces. [9] While the trophozoites cannot survive outside of the host, the cysts can survive for months outside the host—especially in cold water—because they have a slower metabolic rate than the trophozoites. [11] The cysts remain dormant until ingested by a host animal. When a new potential host ingests water or food contaminated with this feces, the cysts gain entry to the gastrointestinal tract of the new host. [12] In the new host, environmental conditions trigger the cyst to produce two trophozoites, which then attach to epithelial cells, starting the cycle anew. [9]

Structure

The trophozoite has an elaborate structure with two nuclei and four pairs of flagella which allow it to swim within the intestinal lumen of the host. It also has an adhesive disk on its ventral surface that enables it to adhere to the intestinal epithelium. The organism lacks Golgi or mitochondria but has mitosomes, which probably evolved from mitochondria. [13] The mitosomes lack mitochondrial genomes but contain proteins from former mitochondrial genes that migrated to the cell nucleus. The trophozoite changes into the cyst form when it comes into contact with certain environmental stressors such as a high pH. The cyst form primarily contains the nucleus, and lacks most structures of the trophozoite form such as the flagella and adhesive disks. This allows the cyst to remain dormant until it is ingested by a new host. At that point, it transforms back into the trophozoite form. [14]

Geographical Prevalence of Giardia duodenalis

The parasite Giardia duodenalis can be found all over the world, in both developing and industrialized nations. However, it is most commonly found in tropical and temperate climates. [15] Giardia duodenalis is common around the world because the parasite resides in bodies of water; typically rivers, lakes, and recreational swimming pools. [16] Additionally, cases of giardiasis tend to be more frequent in developing countries, where the sanitation and overall hygiene is poorer, compared to countries that are more developed and have more advanced sanitary regulations and procedures. [17] In developed nations, giardiasis has a prevalence of 2%-5%, and in developing nations giardiasis has a prevalence of 20%-30%. [18] Giardiasis is the most common intestinal infection that is derived from parasites in both the United States [19] and the United Kingdom. [20] In the United States, it has been discovered that a majority of whom are infected by the Giardia duodenalis parasite tend to reside in more urban areas, and, patients who are infected are more likely to live in the Southern United States. [21]

Prevalence and Epidemiology

G. duodenalis causes an infection called giardiasis. This disease is the cause of both endemic and epidemic disease worldwide and is the most frequently identified intestinal parasite in the United States and Canada. It is estimated to infect over 280 million people world every year [22] resulting over 500,000 deaths. The most affected demographic is children 0 to 4 years of age. Globally G. duodenalis is the most commonly identified protozoal intestinal parasite. In high-income countries, there is an infection rate between 2-5%, and in low and middle-income countries there is an infection rate between 20-30%. [23] Giardia has common seasonal patterns in the distribution of infection rates with highest peaks in the late summer to early fall. [24]

The cyst can survive for weeks to months in cold water, [11] so can be present in contaminated wells and water systems, especially stagnant water sources, such as naturally occurring ponds, storm-water storage systems, and even clean-looking mountain streams. Cysts can also be found on surfaces, soil, food, or water that have been contaminated with feces from infected humans or animals. [25] They may also occur in city reservoirs and persist after water treatment, as the cysts are resistant to conventional water-treatment methods, such as chlorination and ozonolysis. [11] Zoonotic transmission is also possible, so 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").[ citation needed ]

In addition to waterborne sources, Giardia infections are more commonly found in children than adults, this is believed to be due to fecal-oral transmission of the cysts. Depending on the geographical area, from 1-68% of children may be infected. Those who work with children are also at risk of being infected, as are family members of infected individuals. 7% of children aged 1 to 3 years and 11% of infants and toddlers tested for admission to day-care centers were found to be infected. [26] Not all Giardia infections are symptomatic, and many people can unknowingly serve as carriers of the parasite. Re- infection and chronic infections of the parasite can occur. [27] [ citation needed ]

Ecology

Giardia infects humans, but is also one of the most common parasites infecting cats, dogs, and birds. Mammalian hosts also include dozens of species, [28] including cattle, sheep, [29] and goats. [29]

Cats can be cured easily, and 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. This parasite is deadly for chinchillas, so extra care must be taken by providing them with safe water. 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. Infected dogs can be isolated and treated, or the entire pack at a kennel can be presumptively treated together. Kennels and 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.[ citation needed ]

Cell biology

Giardia trophozoites stained with Giemsa; 100x magnification Giardia trophozoites Giemsa.tif
Giardia trophozoites stained with Giemsa; 100x magnification

G. duodenalis trophozoites are pear-shaped cells, 10 to 20 μm long, 7 to 10 μm across, and 2 to 4 μm thick. [9] [10] They are motile by way of four pairs of flagella, which propel the trophozoites through the intestine. [10] Notably, each G. duodenalis cell has two nuclei, both of which actively transcribe genes. [9] Adjacent to the nucleus, G. duodenalis cells have an endoplasmic reticulum that extends through much of the cell. [30] Trophozoites about to differentiate into cysts also contain prominent vesicles termed encystation-specific vesicles that disappear once cyst wall construction begins. [30] Unlike most other eukaryotes, G. duodenalis cells contain no visible mitochondria, but instead contains a substantially reduced metabolic organelle termed a mitosome. [10] Additionally, cells appear to contain no Golgi bodies, and instead the secretory system consists entirely of the endoplasmic reticulum and numerous vesicles dispersed throughout the cell, termed peripheral vesicles. [30] Peripheral vesicles are responsible both for taking up extracellular nutrients, and expelling waste outside the cell. [31] Each cell also contains a pair of rigid structures called median bodies which make up part of the G. lamblia cytoskeleton. [9] Trophozoites adhere to host epithelial cells via a specialized disk-shaped organelle called the ventral disk. [9]

Cysts are oval-shaped cells slightly smaller than trophozoites. [10] They lack flagella, and are covered by a smooth, clear cyst wall. [10] Each cyst contains the organelles for two trophzoites: four nuclei, two ventral disks, etc. [10]

Multiple views of a G. lamblia cyst imaged by confocal microscopy: Bar = 10 micrometers (A) Cyst imaged by transmission (differential interference contrast) (B) Cyst wall selectively imaged through use of fluorescent-labelled antibody (C) Cyst imaged through use of carboxy fluorescein diacetate, a viability stain (D) Composite image of (B) and (C) (E) Composite image of (A), (B), and (C) Giardia.jpg
Multiple views of a G. lamblia cyst imaged by confocal microscopy: Bar = 10 micrometers
(A) Cyst imaged by transmission (differential interference contrast)
(B) Cyst wall selectively imaged through use of fluorescent-labelled antibody
(C) Cyst imaged through use of carboxy fluorescein diacetate, a viability stain
(D) Composite image of (B) and (C)
(E) Composite image of (A), (B), and (C)

Metabolism

G. duodenalis primarily generates its energy by breaking down glucose via glycolysis, as well as the arginine deiminase pathway. It is unable to synthesize nucleotides on its own, instead salvaging them from its host. Synthesis of iron–sulfur clusters is done in a double-membrane-bound compartment called the mitosome, which is likely a remnant of mitochondria. [13] Each cell contains 25 to 100 mitosomes divided into two categories - peripheral mitosomes, which are scattered throughout the cell, and central mitosomes, which gather at the center of the cell for unknown reasons. [32] As in mitochondria, proteins with a certain peptide signal sequence are trafficked to and imported into the mitosome. Unlike mitochondria, mitosomes have no genome of their own. All mitosomal genes are encoded by the Giardia nuclear genome. [13]

Genetics

Giardia and the other diplomonads are unique in their possession of two cell nuclei that are similar in appearance, DNA content, transcription, and time of replication. Giardia is a polyploid organism, with at least four, and perhaps eight or more, copies of each of five chromosomes per organism. [33] The genome has been sequenced and was published in 2007, although the sequence contains several gaps. The sequence is about 12 million base pairs and contains about 5000 protein-coding genes. [34] The GC-content is 46%. Trophozoites have a ploidy of four and the ploidy of cysts is eight, which in turn raises the question of how Giardia maintains homogeneity between the chromosomes of the same and opposite nuclei. Modern sequencing technologies have been used to resequence different strains. [35]

Immunology

Infections with Giardia are self-limited in immunocompetent individuals, while people with immunodeficiency disorders may develop chronic giardiasis.[ citation needed ] During the infection different mechanisms from the innate and adaptive immune system are activated. The first physical barrier is the mucus layer where the organism interacts with epithelial, immune cells, and some antimicrobial peptides released by those cells as well as nitric oxide and inflammatory cytokines like interleukin 6. TLR2 and TLR4 also can be activated by Giardia. [36] The T-cell response in giardiasis includes T helper cells and cytotoxic T cells, and the production of IgA by B cells also helps to eliminate the infection. [37]

Evolution

Giardia had been assumed to be primitively asexual and with no means of transferring DNA between nuclei. These assumptions made explaining the remarkably low level of allelic heterozygosity (< 0.01%) in the genome isolate, WB, very difficult, but all those assumptions of asexuality are now in doubt, with population genetics providing evidence for recombination [38] and the identification of meiotic genes, evidence for recombination among isolates and the evidence for exchange of genetic material between nuclei during the process of encystation. [39]

These findings on sexuality in Giardia, above, have important implications for understanding the origin of sexual reproduction in eukaryotes. Though sexual reproduction is widespread among extant eukaryotes, until recently, sex seemed unlikely to be a primordial and fundamental feature of eukaryotes. A probable reason for the view that sex may not be fundamental to eukaryotes was that sexual reproduction previously appeared to be lacking in certain human pathogenic single-celled eukaryotes (e.g. Giardia) that diverged from early ancestors in the eukaryotic lineage.[ citation needed ]

In addition to the evidence cited above for recombination in Giardia, Malik et al. [40] reported that many meiosis specific genes occur in the Giardia genome, and further that homologs of these genes also occur in another unicellular eukaryote, Trichomonas vaginalis . Because these two species are descendants of lineages that are highly divergent among eukaryotes, Malik et al. [40] suggested that these meiotic genes were present in a common ancestor of all eukaryotes. Thus, on this view, the earliest ancestor of eukaryotes was likely capable of sexual reproduction. Furthermore, Dacks and Roger [41] proposed, based on phylogenetic analysis, that facultative sex was present in the common ancestor of all eukaryotes. Bernstein et al. also reviewed evidence in support of this view. [42]

Eight genotype assemblages of G. duodenalis have been recognized to date (A-H). [28] Genotyping of G. duodenalis isolated from various hosts has shown that assemblages A and B infect the largest range of host species, and appear to be the main (or possibly only) G. duodenalis assemblages that undeniably infect human subjects. [28]

Research

Frances Gillin of the University of California, San Diego, and her colleagues cultivated the entire lifecycle of this parasite in the laboratory, and identified biochemical cues in the host's digestive system that trigger Giardia's lifecycle transformations. [43] [44] They also uncovered several ways in which the parasite evades the defences 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 (called antigenic variation). Gillin's work reveals why Giardia infections are extremely persistent and prone to recur. In addition, these insights into its biology and survival techniques may enable scientists to develop better strategies to understand, prevent, and treat Giardia infections.[ citation needed ]

In December 2008, Nature published an article showing the discovery of an RNA interference mechanism that allows Giardia to switch variant-specific surface proteins to avoid host immune response. [45] The discovery was made by the team working at the Biochemistry and Molecular Biology Laboratory, School of Medicine, Catholic University of Cordoba, Argentina, led by Dr. Hugo Lujan.[ citation needed ]

The main congress about Giardia is the International Giardia and Cryptosporidium Conference. A summary of results presented at the most recent edition (2019, in Rouen, France) is available. [46]

History

A Giardia trophozoite, drawn by Vilem Lambl and published in 1859 Giardia drawing Lambl 1859.jpg
A Giardia trophozoite, drawn by Vilém Lambl and published in 1859
Drawings of a Giardia trophozoite and cyst by Charles E. Simon in 1921 CE Simon Giardia Drawings 1921.jpg
Drawings of a Giardia trophozoite and cyst by Charles E. Simon in 1921

The first likely description of Giardia was in 1681 by Antonie van Leeuwenhoek, who in a letter to Robert Hooke, described "animalcules" resembling Giardia trophozoites in his stool. [9] [47] The next known description of Giardia wasn't until 1859, when Czech physician Vilém Lambl published a description of the trophozoite stages he saw in the stool of a pediatric patient. Lambl termed the organism Cercomonas intestinalis. [48] In 1888, Raphaël Blanchard renamed the parasite Lamblia intestinalis in Lambl's honor. [48] In 1915, Charles Stiles renamed the organism Giardia lamblia in honor of both Lambl and Professor Alfred Mathieu Giard of Paris. [48] [49] In 1921, Charles E. Simon published a detailed description of the parasite's morphology. [9]

See also

Related Research Articles

<i>Entamoeba</i> Genus of internal parasites

Entamoeba is a genus of Amoebozoa found as internal parasites or commensals of animals. In 1875, Fedor Lösch described the first proven case of amoebic dysentery in St. Petersburg, Russia. He referred to the amoeba he observed microscopically as Amoeba coli; however, it is not clear whether he was using this as a descriptive term or intended it as a formal taxonomic name. The genus Entamoeba was defined by Casagrandi and Barbagallo for the species Entamoeba coli, which is known to be a commensal organism. Lösch's organism was renamed Entamoeba histolytica by Fritz Schaudinn in 1903; he later died, in 1906, from a self-inflicted infection when studying this amoeba. For a time during the first half of the 20th century the entire genus Entamoeba was transferred to Endamoeba, a genus of amoebas infecting invertebrates about which little is known. This move was reversed by the International Commission on Zoological Nomenclature in the late 1950s, and Entamoeba has stayed 'stable' ever since.

<i>Giardia</i> Genus of flagellate intestinal eukaryotes parasitic in various vertebrate

Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada that colonise and reproduce in the small intestines of several vertebrates, causing the disease giardiasis. Their life cycle alternates between a swimming trophozoite and an infective, resistant cyst. Giardia were first described by the Dutch microscopist Antonie van Leeuwenhoek in 1681. The genus is named after French zoologist Alfred Mathieu Giard.

<i>Entamoeba histolytica</i> Anaerobic parasitic protist

Entamoeba histolytica is an anaerobic parasitic amoebozoan, part of the genus Entamoeba. Predominantly infecting humans and other primates causing amoebiasis, E. histolytica is estimated to infect about 35-50 million people worldwide. E. histolytica infection is estimated to kill more than 55,000 people each year. Previously, it was thought that 10% of the world population was infected, but these figures predate the recognition that at least 90% of these infections were due to a second species, E. dispar. Mammals such as dogs and cats can become infected transiently, but are not thought to contribute significantly to transmission.

<span class="mw-page-title-main">Giardiasis</span> Parasitic disease that results in diarrhea

Giardiasis is a parasitic disease caused by Giardia duodenalis. Infected individuals who experience symptoms may have diarrhoea, abdominal pain, and weight loss. Less common symptoms include vomiting and blood in the stool. Symptoms usually begin one to three weeks after exposure and, without treatment, may last two to six weeks or longer.

<i>Trichomonas vaginalis</i> Species of parasite that causes sexually transmitted infections

Trichomonas vaginalis is an anaerobic, flagellated protozoan parasite and the causative agent of a sexually transmitted disease called trichomoniasis. It is the most common pathogenic protozoan that infects humans in industrialized countries. Infection rates in men and women are similar but women are usually symptomatic, while infections in men are usually asymptomatic. Transmission usually occurs via direct, skin-to-skin contact with an infected individual, most often through vaginal intercourse. The WHO has estimated that 160 million cases of infection are acquired annually worldwide. The estimates for North America alone are between 5 and 8 million new infections each year, with an estimated rate of asymptomatic cases as high as 50%. Usually treatment consists of metronidazole and tinidazole.

<i>Entamoeba coli</i> Species of parasitic amoeba

Entamoeba coli is a non-pathogenic species of Entamoeba that frequently exists as a commensal parasite in the human gastrointestinal tract. E. coli is important in medicine because it can be confused during microscopic examination of stained stool specimens with the pathogenic Entamoeba histolytica. This amoeba does not move much by the use of its pseudopod, and creates a "sur place (non-progressive) movement" inside the large intestine. Usually, the amoeba is immobile, and keeps its round shape. This amoeba, in its trophozoite stage, is only visible in fresh, unfixed stool specimens. Sometimes the Entamoeba coli have parasites as well. One is the fungus Sphaerita spp. This fungus lives in the cytoplasm of the E. coli. While this differentiation is typically done by visual examination of the parasitic cysts via light microscopy, new methods using molecular biology techniques have been developed. The scientific name of the amoeba, E. coli, is often mistaken for the bacterium, Escherichia coli. Unlike the bacterium, the amoeba is mostly harmless, and does not cause as many intestinal problems as some strains of the E. coli bacterium. To make the naming of these organisms less confusing, "alternate contractions" are used to name the species for the purpose making the naming easier; for example, using Esch. coli and Ent. coli for the bacterium and amoeba, instead of using E. coli for both.

<span class="mw-page-title-main">Diplomonad</span> Group of mostly parasitic flagellates

The diplomonads are a group of flagellates, most of which are parasitic. They include Giardia duodenalis, which causes giardiasis in humans. They are placed among the metamonads, and appear to be particularly close relatives of the retortamonads.

A trophozoite is the activated, feeding stage in the life cycle of certain protozoa such as malaria-causing Plasmodium falciparum and those of the Giardia group. The complementary form of the trophozoite state is the thick-walled cyst form. They are often different from the cyst stage, which is a protective, dormant form of the protozoa. Trophozoites are often found in the host's body fluids and tissues and in many cases, they are the form of the protozoan that causes disease in the host. In the protozoan, Entamoeba histolytica it invades the intestinal mucosa of its host, causing dysentery, which aid in the trophozoites traveling to the liver and leading to the production of hepatic abscesses.

<i>Cryptosporidium</i> Genus of single-celled organisms

Cryptosporidium, sometimes called crypto, is an apicomplexan genus of alveolates which are parasites that can cause a respiratory and gastrointestinal illness (cryptosporidiosis) that primarily involves watery diarrhea, sometimes with a persistent cough.

<i>Retortamonas</i> Unicellular organism

Retortamonas is a genus of flagellated excavates. It is one of only two genera belonging to the family Retortamonadidae along with the genus Chilomastix. The genus parasitizes a large range of hosts including humans. Species within this genus are considered harmless commensals which reside in the intestine of their host. The wide host diversity is a useful factor given that species are distinguished based on their host rather than morphology. This is because all species share similar morphology, which would present challenges when trying to make classifications based on structural anatomy. Although Retortamonas currently includes over 25 known species, it is possible that some defined species are synonymous, given that such overlapping species have been discovered in the past. Further efforts into learning about this genus must be done such as cross-transmission testing as well as biochemical and genetic studies. One of the most well-known species within this genus is Retortamonas intestinalis, a human parasite that lives in the large intestine of humans.

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<i>Blastocystis</i> Genus of single-celled organisms

Blastocystis is a genus of single-celled parasites belonging to the Stramenopiles that includes algae, diatoms, and water molds. There are several species, living in the gastrointestinal tracts of species as diverse as humans, farm animals, birds, rodents, reptiles, amphibians, fish, and cockroaches. Blastocystis has low host specificity, and many different species of Blastocystis can infect humans, and by current convention, any of these species would be identified as Blastocystis hominis.

The discovery of disease-causing pathogens is an important activity in the field of medical science. Many viruses, bacteria, protozoa, fungi, helminths, and prions are identified as a confirmed or potential pathogen. In the United States, a Centers for Disease Control and Prevention program, begun in 1995, identified over a hundred patients with life-threatening illnesses that were considered to be of an infectious cause but that could not be linked to a known pathogen. The association of pathogens with disease can be a complex and controversial process, in some cases requiring decades or even centuries to achieve.

<span class="mw-page-title-main">Protozoan infection</span> Parasitic disease caused by a protozoan

Protozoan infections are parasitic diseases caused by organisms formerly classified in the kingdom Protozoa. These organisms are now classified in the supergroups Excavata, Amoebozoa, Harosa, and Archaeplastida. They are usually contracted by either an insect vector or by contact with an infected substance or surface.

Spironucleus salmonicida is a species of fish parasite. It is a flagellate adapted to micro-aerobic environments that causes systemic infections in salmonid fish. The species creates foul-smelling, pus-filled abscesses in muscles and internal organs of aquarium fish. In the late 1980s when the disease was first reported, it was believed to be caused by Spironucleus barkhanus. Anders Jørgensen was the person that found out what species really caused the disease.

Spironucleus is a diplomonad genus that is bilaterally symmetrical and can be found in various animal hosts. This genus is a binucleate flagellate, which is able to live in the anaerobic conditions of animal intestinal tracts. A characteristic of Spironucleus that is common to all metamonads is that it does not have aerobic mitochondria, but instead rely on hydrogenosomes to produce energy. Spironucleus has six anterior and two posterior flagella. The life cycle of Spironucleus involves one active trophozoite stage and one inactive cyst stage. Spironucleus undergoes asexual reproduction via longitudinal binary fission. Spironucleusvortens can cause lateral line erosion in freshwater anglefish. Spironucleuscolumbae is found to cause hexamitiasis in pigeons. Finally, Spironucleusmuris is found to cause illnesses of the digestive system in mice, rats, and hamsters. The genome of Spironucleus has been studied to exhibit the role of lateral gene transfer from prokaryotes in allowing for anaerobic metabolic processes in diplomonads.

<span class="mw-page-title-main">Amoebiasis</span> Human disease caused by amoeba protists

Amoebiasis, or amoebic dysentery, is an infection of the intestines caused by a parasitic amoeba Entamoeba histolytica. Amoebiasis can be present with no, mild, or severe symptoms. Symptoms may include lethargy, loss of weight, colonic ulcerations, abdominal pain, diarrhea, or bloody diarrhea. Complications can include inflammation and ulceration of the colon with tissue death or perforation, which may result in peritonitis. Anemia may develop due to prolonged gastric bleeding.

<i>Dientamoeba fragilis</i> Parasite of humans, pigs and gorillas

Dientamoeba fragilis is a species of single-celled excavates found in the gastrointestinal tract of some humans, pigs and gorillas. It causes gastrointestinal upset in some people, but not in others. It is an important cause of traveller's diarrhoea, chronic diarrhoea, fatigue and, in children, failure to thrive. Despite this, its role as a "commensal, pathobiont, or pathogen" is still debated. D. fragilis is one of the smaller parasites that are able to live in the human intestine. Dientamoeba fragilis cells are able to survive and move in fresh feces but are sensitive to aerobic environments. They dissociate when in contact or placed in saline, tap water or distilled water.

<i>Chilomastix</i>

Chilomastix is a genus of pyriform excavates within the family Retortamonadidae All species within this genus are flagellated, structured with three flagella pointing anteriorly and a fourth contained within the feeding groove. Chilomastix also lacks Golgi apparatus and mitochondria but does possess a single nucleus. The genus parasitizes a wide range of vertebrate hosts, but is known to be typically non-pathogenic, and is therefore classified as harmless. The life cycle of Chilomastix lacks an intermediate host or vector. Chilomastix has a resistant cyst stage responsible for transmission and a trophozoite stage, which is recognized as the feeding stage. Chilomastix mesnili is one of the more studied species in this genus due to the fact it is a human parasite. Therefore, much of the information on this genus is based on what is known about this one species.

References

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