Giardiasis

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Giardiasis
Other namesBeaver fever, giardia
Giardia lamblia SEM 8698 lores.jpg
Giardia cell viewed with scanning electron microscope
Specialty Infectious disease, gastroenterology
Symptoms Diarrhea, abdominal pain, weight loss, nausea [1]
Usual onset1 to 3 weeks after exposure [2]
Causes Giardia duodenalis spread mainly through contaminated food or water [1]
Risk factors Hypogammaglobulinemia
Diagnostic method Stool testing [1]
Differential diagnosis Irritable bowel syndrome [1]
PreventionImproved sanitation [1]
Treatment Antiprotozoal medications
Medication Tinidazole, metronidazole [1]
FrequencyUp to 7% (developed world), up to 30% (developing world) [1]

Giardiasis is a parasitic disease caused by Giardia duodenalis (also known as G. lamblia and G. intestinalis). [3] Infected individuals who experience symptoms (about 10% have no symptoms) may have diarrhea, abdominal pain, and weight loss. [1] Less common symptoms include vomiting and blood in the stool. [1] Symptoms usually begin one to three weeks after exposure and, without treatment, may last two to six weeks or longer. [4]

Contents

Giardiasis usually spreads when Giardia duodenalis cysts within faeces contaminate food or water that is later consumed orally. [1] The disease can also spread between people and through other animals. [1] Cysts may survive for nearly three months in cold water. [1] Giardiasis is diagnosed via stool tests. [1]

Prevention may be improved through proper hygiene practices. [1] Asymptomatic cases often do not need treatment. [1] When symptoms are present, treatment is typically provided with either tinidazole or metronidazole. [1] Infection may cause a person to become lactose intolerant, so it is recommended to temporarily avoid lactose following an infection. [1] Resistance to treatment may occur in some patients. [1]

Giardiasis occurs worldwide. [5] It is one of the most common parasitic human diseases. [3] Infection rates are as high as 7% in the developed world and 30% in the developing world. [1] In 2013, there were approximately 280 million people worldwide with symptomatic cases of giardiasis. [3] The World Health Organization classifies giardiasis as a neglected disease. [1] It is popularly known as beaver fever [6] in North America.

Signs and symptoms

Symptoms vary from none to severe diarrhoea with poor absorption of nutrients. [5] The cause of this wide range in severity of symptoms is not fully known but the intestinal flora of the infected host may play a role. [7] [8] Diarrhoea is less likely to occur in people from developing countries. [7]

Symptoms typically develop 9–15 days after exposure, [9] but may occur as early as one day. [5] The most common and prominent symptom is chronic diarrhoea, which can occur for weeks or months if untreated. [10] [11] Diarrhoea is often greasy and foul-smelling, with a tendency to float. [10] [4] This characteristic diarrhoea is often accompanied by several other symptoms, including gas, abdominal cramps, and nausea or vomiting. [10] [4] Some people also experience symptoms outside of the gastrointestinal tract, such as itchy skin, hives, and swelling of the eyes and joints, although these are less common. [4] Fever occurs in only about 15% of infected people, [12] despite the nickname "beaver fever". [6]

Prolonged disease is often characterised by diarrhoea and malabsorption of nutrients in the intestine. [10] This malabsorption causes fatty stools, substantial weight loss, and fatigue. [10] Additionally, those with giardiasis often have difficulty absorbing lactose, vitamin A, folate, and vitamin B12. [11] [4] In children, prolonged giardiasis can cause failure to thrive and may impair mental development. [10] [11] Symptomatic infections are well recognised as causing lactose intolerance, [13] which, though usually temporary, may become permanent. [14] [15]

Cause

Infectiology - Giarda intestinalis - Cyst -- Smart-Servier.png
Infectiology - Giarda intestinalis - Trophozoite -- Smart-Servier.png
Cyst (left) and trophozoite (right) of Giarda intestinalis

Giardiasis is caused by the protozoan Giardia duodenalis . [16] The infection occurs in many animals, including beavers, other rodents, cows, and sheep. [16] Animals are believed to play a role in keeping infections present in an environment. [16]

G. duodenalis has been sub-classified into eight genetic assemblages (designated A–H). [17] 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 and possibly only G. duodenalis assemblages that infect humans. [17] [18]

Risk factors

According to the United States Centers for Disease Control and Prevention (CDC), people at greatest risk of infection are: [19]

Factors that increase infection risk for people from developed countries include changing nappies/diapers, consuming raw food, owning a dog, and travelling in the developing world. [1] However, 75% of infections in the United Kingdom are acquired in the UK, not through travel elsewhere. [1] In the United States, giardiasis occurs more often in summer, which is believed to be due to a greater amount of time spent on outdoor activities and travelling in the wilderness. [16]

Transmission

Giardiasis is transmitted via the faecal-oral route with the ingestion of cysts. [9] Primary routes are personal contact and contaminated water and food. [9] The cysts can stay infectious for up to three months in cold water. [16]

Many people with Giardia infections have no or few symptoms. [20] They may, however, still spread the disease. [20]

Pathophysiology

Life cycle of Giardia Giardia LifeCycle.gif
Life cycle of Giardia

The life cycle of Giardia consists of a cyst form and a trophozoite form. [8] The cyst form is infectious and once it has found a host, transforms into the trophozoite form. [8] This trophozoite attaches to the intestinal wall and replicates within the gut. [8] As trophozoites continue along the gastrointestinal tract, they convert back to their cyst form which is then excreted with faeces. [1] Ingestion of only a few of these cysts is needed to generate infection in another host. [21]

Infection with Giardia results in decreased expression of brush border enzymes, morphological changes to the microvillus, increased intestinal permeability, and programmed cell death of small intestinal epithelial cells. [22] Both trophozoites and cysts are contained within the gastrointestinal tract and do not invade beyond it. [23]

The attachment of trophozoites causes villous flattening and inhibition of enzymes that break down disaccharide sugars in the intestines. [7] [22] Ultimately, the community of microorganisms that lives in the intestine may overgrow and may be the cause of further symptoms, though this idea has not been fully investigated. The alteration of the villi leads to an inability of nutrient and water absorption from the intestine, resulting in diarrhoea, one of the predominant symptoms. [22] In the case of asymptomatic giardiasis, there can be malabsorption with or without histological changes to the small intestine. The degree to which malabsorption occurs in symptomatic and asymptomatic cases is highly varied.[ citation needed ]

The species Giardia intestinalis uses enzymes that break down proteins to attack the villi of the brush border and appears to increase crypt cell proliferation and crypt length of crypt cells existing on the sides of the villi. On an immunological level, activated host T lymphocytes attack endothelial cells that have been injured to remove the cell. [7] This occurs after the disruption of proteins that connect brush border endothelial cells to one another. [22] The result is increased intestinal permeability. [22]

There appears to be a further increase in programmed enterocyte cell death by Giardia intestinalis, which further damages the intestinal barrier and increases permeability. [22] There is significant upregulation of the programmed cell death cascade by the parasite, and substantial downregulation of the anti-apoptotic protein Bcl-2 and upregulation of the proapoptotic protein Bax. [7] These connections suggest a role of caspase-dependent apoptosis in the pathogenesis of giardiasis. [7]

Giardia protects its growth by reducing the formation of the gas nitric oxide by consuming all local arginine, which is the amino acid necessary to make nitric oxide. [7] Arginine starvation is known to be a cause of programmed cell death, and local removal is a strong apoptotic agent. [24]

Host defence

Host defence against Giardia consists of natural barriers, production of nitric oxide, and activation of the innate and adaptive immune systems.[ citation needed ]

Natural barriers

Natural barriers defend against the parasite entering the host's body. Natural barriers consist of mucus layers, bile salt, proteases, and lipases. Additionally, peristalsis and the renewal of enterocytes provide further protection against parasites. [25] [26]

Nitric oxide production

Nitric oxide does not kill the parasite, but it inhibits the growth of trophozoites as well as excystation and encystation. [27] [28]

Innate immune system

Lectin pathway of complement

The lectin pathway of complement is activated by mannose-binding lectin (MBL) which binds to N-acetylglucosamine. N-acetylglucosamine is a ligand for MBL and is present on the surface of Giardia. [29]

The classical pathway of complement

The classical pathway of complement is activated by antibodies specific against Giardia.[ citation needed ]

Adaptive immune system

Antibodies

Antibodies inhibit parasite replication and also induce parasite death via the classical pathway of complement.[ citation needed ]

Infection with Giardia typically results in a strong antibody response against the parasite. While IgG is made in significant amounts, IgA is believed to be more important in parasite control. IgA is the most abundant isotype in intestinal secretions, and it is also the dominant isotype in a mother's milk. Antibodies in a mother's milk protect children against giardiasis (passive immunisation). [30]

T-cells

The major aspect of adaptive immune responses is the T-cell response. Giardia is an extracellular pathogen. Therefore CD4+ helper T-cells are primarily responsible for this protective effect. [31]

One role of helper T-cells is to promote antibody production and isotype switching. Other roles include cytokine production (Il-4, IL-9) to help recruit other effector cells of the immune response. [31] [32]

Diagnosis

A duodenal biopsy may incidentally detect Giardia organisms, as in this H&E stained sample. Histopathology of Giardia lamblia in duodenum.png
A duodenal biopsy may incidentally detect Giardia organisms, as in this H&E stained sample.

Although hydrogen breath tests indicate poorer rates of carbohydrate absorption in those asymptomatically infected, such tests are not diagnostic of infection. [38] Serological tests are not helpful in diagnosis. [1]

Prevention

The CDC recommends hand-washing and avoiding potentially contaminated food and untreated water. [39]

Boiling water contaminated with Giardia effectively kills infectious cysts. [40] Chemical disinfectants or filters may be used. [41] [42] Iodine-based disinfectants are preferred over chlorination as the latter is ineffective at destroying cysts. [43] [44]

Although the evidence linking the drinking of water in the North American wilderness and giardiasis has been questioned, a number of studies raise concern. [45] Most if not all CDC verified backcountry giardiasis outbreaks have been attributed to water. Surveillance data (for 2013 and 2014) reports six outbreaks (96 cases) of waterborne giardiasis contracted from rivers, streams or springs [46] and less than 1% of reported giardiasis cases are associated with outbreaks. [47]

Person-to-person transmission accounts for the majority of Giardia infections and is usually associated with poor hygiene and sanitation. Giardia is often found on the surface of the ground, in the soil, in undercooked foods, and in water, and on hands that have not been properly cleaned after handling infected faeces. [48] 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 faecal-oral contamination. Additionally, nappy/diaper changing and inadequate handwashing 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. [49]

Vaccine

There are no vaccines for humans yet, however, there are several vaccine candidates in development. They are targeting: recombinant proteins, DNA vaccines, variant-specific surface proteins (VSP), cyst wall proteins (CWP), giadins, and enzymes. [50] Researchers at CONICET have produced an oral vaccine after engineering customised proteins mimicking those expressed on the surface of Giardia trophozoites. The vaccine has proven effective in mice. [51] [52]

At present, one commercially available vaccine exists – GiardiaVax, made from G. lamblia whole trophozoite lysate. It is a vaccine for veterinary use only in dogs and cats. GiardiaVax should promote the production of specific antibodies. [53]

Treatment

Treatment is not always necessary as the infection usually resolves on its own. [7] However, if the illness is acute or symptoms persist and medications are needed to treat it, a nitroimidazole medication is used such as metronidazole, tinidazole, secnidazole or ornidazole. [9]

The World Health Organisation and Infectious Disease Society of America recommend metronidazole as first-line therapy. [54] [55] The US CDC lists metronidazole, tinidazole, and nitazoxanide as effective first-line therapies; [56] of these three, only nitazoxanide and tinidazole are approved for the treatment of giardiasis by the US FDA. [57] [58] [59] A meta-analysis published by the Cochrane Collaboration in 2012 found that compared to the standard of metronidazole, albendazole had equivalent efficacy while having fewer side effects, such as gastrointestinal or neurologic issues. [60] Other meta-analyses have reached similar conclusions. [61] Both medications need a five to ten-day-long course; albendazole is taken once a day, while metronidazole needs to be taken three times a day. The evidence for comparing metronidazole to other alternatives such as mebendazole, tinidazole, or nitazoxanide was felt to be of very low quality. [60] While tinidazole has side effects and efficacy similar to those of metronidazole, it is administered with a single dose. [20]

Resistance has been seen clinically to both nitroimidazoles and albendazole, but not nitazoxanide, though nitazoxanide resistance has been induced in research laboratories. [21] [62] The exact mechanism of resistance to all of these medications is not well understood. [62] In the case of nitroimidazole-resistant strains of Giardia, other drugs are available which have shown efficacy in treatment including quinacrine, nitazoxanide, bacitracin zinc, furazolidone and paromomycin. [20] Mepacrine may also be used for refractory cases. [21]

Probiotics, when given in combination with the standard treatment, have been shown to assist with clearance of Giardia. [63]

During pregnancy, paromomycin is the preferred treatment drug because of its poor intestinal absorption, resulting in less exposure to the foetus. [64] Alternatively, metronidazole can be used after the first trimester as there has been wide experience in its use for trichomonas in pregnancy. [20] [65]

Prognosis

In people with a properly functioning immune system, infection may resolve without medication. [7] A small portion, however, develop a chronic infection. [7] People with an impaired immune system are at higher risk of chronic infection. [7] Medication is an effective cure for nearly all people although there is growing drug-resistance. [1] [66] [21]

Children with chronic giardiasis are at risk for failure to thrive as well as more long-lasting sequelae such as growth stunting. [67] Up to half of infected people develop a temporary lactose intolerance leading to symptoms that may mimic a chronic infection. [1] Some people experience post-infectious irritable bowel syndrome after the infection has cleared. [7] Giardiasis has also been implicated in the development of food allergies. [7] This is thought to be due to its effect on intestinal permeability. [7]

Epidemiology

Rates of giardiasis in 2005 in the United States US giardiasis incidence 2005.gif
Rates of giardiasis in 2005 in the United States

In some developing countries Giardia is present in 30% of the population. [16] In the United States it is estimated that it is present in 3–7% of the population. [16] Giardiasis is associated with impaired growth and development in children, particularly influencing a country's economic growth by affecting Disability Adjusted Life Year (DALY) rates. [68] [69]

The number of reported cases in the United States in 2018 was 15,584. [70] All states that classify giardiasis as a notifiable disease had cases of giardiasis. [70] The states of Illinois, Kentucky, Mississippi, North Carolina, Oklahoma, Tennessee, Texas, and Vermont did not notify the Center for Disease Control regarding cases in 2018. [70] There are seasonal trends associated with giardiasis. [71] July, August, and September are the months with the highest incidence of giardiasis in the United States. [72]

In the ECDC's (European Centre for Disease Prevention and Control) annual epidemiological report containing 2014 data, 17,278 confirmed giardiasis cases were reported by 23 of the 31 countries that are members of the EU/EEA. [73] Germany reported the highest number at 4,011 cases. [73] Following Germany, the UK reported 3,628 confirmed giardiasis cases. Together, this accounts for 44% of total reported cases. [73]

Research

Some intestinal parasitic infections may play a role in irritable bowel syndrome [74] and other long-term sequelae such as chronic fatigue. [75] [76] The mechanism of transformation from cyst to trophozoites has not been characterised [8] but may help develop drug targets for treatment-resistant Giardia. The interaction between Giardia and host immunity, internal flora, and other pathogens is not well understood. [7] In vitro cell cultures have been widely used to study host-parasite interactions, and human enteroids are now being used as non-transformed intestinal epithelial cell infection models for G. intestinalis and other pathogens. [77]

The main congress about giardiasis is the "International Giardia and Cryptosporidium Conference" (IGCC). A summary of results presented at the most recent edition (2019, in Rouen, France) is available. [78]

Other animals

In both cats and dogs, giardiasis usually responds to metronidazole and fenbendazole. Metronidazole in pregnant cats can cause developmental malformations. [79] Many cats dislike the taste of fenbendazole. [79] Giardiasis has been shown to decrease weight in livestock. [7]

Related Research Articles

<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 seen by the Dutch microscopist Antonie van Leeuwenhoek in 1681. The genus is named after French zoologist Alfred Mathieu Giard.

<i>Giardia duodenalis</i> Parasitic microorganism that causes giardiasis

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. The parasite attaches to the intestinal epithelium by an adhesive disc or sucker, and reproduces via binary fission. Giardiasis does not spread to other parts of the gastrointestinal tract, but remains confined to the lumen of the small intestine. 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.

<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 ball 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.

<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. It is 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.

Wilderness-acquired diarrhea is a variety of traveler's diarrhea in which backpackers and other outdoor enthusiasts are affected. Potential sources are contaminated food or water, or "hand-to-mouth", directly from another person who is infected. Cases generally resolve spontaneously, with or without treatment, and the cause is typically unknown. The National Outdoor Leadership School has recorded about one incident per 5,000 person-field days by following strict protocols on hygiene and water treatment. More limited, separate studies have presented highly varied estimated rates of affliction that range from 3 percent to 74 percent of wilderness visitors. One survey found that long-distance Appalachian Trail hikers reported diarrhea as their most common illness. Based on reviews of epidemiologic data and literature, some researchers believe that the risks have been over-stated and are poorly understood by the public.

<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.

<span class="mw-page-title-main">Balantidiasis</span> Medical condition

Balantidiasis is a protozoan infection caused by infection with Balantidium coli.

Dientamoebiasis is a medical condition caused by infection with Dientamoeba fragilis, a single-cell parasite that infects the lower gastrointestinal tract of humans. It is an important cause of traveler's diarrhea, chronic abdominal pain, chronic fatigue, and failure to thrive in children.

<span class="mw-page-title-main">Nitazoxanide</span> Broad-spectrum antiparasitic and antiviral medication

Nitazoxanide, sold under the brand name Alinia among others, is a broad-spectrum antiparasitic and broad-spectrum antiviral medication that is used in medicine for the treatment of various helminthic, protozoal, and viral infections. It is indicated for the treatment of infection by Cryptosporidium parvum and Giardia lamblia in immunocompetent individuals and has been repurposed for the treatment of influenza. Nitazoxanide has also been shown to have in vitro antiparasitic activity and clinical treatment efficacy for infections caused by other protozoa and helminths; evidence as of 2014 suggested that it possesses efficacy in treating a number of viral infections as well.

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">Diloxanide</span> Medication for amoebic gut infections

Diloxanide is a medication used to treat amoeba infections. In places where infections are not common, it is a second line treatment after paromomycin when a person has no symptoms. For people who are symptomatic, it is used after treatment with metronidazole or tinidazole. It is taken by mouth.

<span class="mw-page-title-main">Blastocystosis</span> Medical condition

Blastocystosis refers to a medical condition caused by infection with Blastocystis. Blastocystis is a protozoal, single-celled parasite that inhabits the gastrointestinal tracts of humans and other animals. Many different types of Blastocystis exist, and they can infect humans, farm animals, birds, rodents, amphibians, reptiles, fish, and even cockroaches. Blastocystosis has been found to be a possible risk factor for development of irritable bowel syndrome.

<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.

<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> Genus of flagellates

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.

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