Blastocystosis refers to a medical condition caused by infection with ''
Blastocystis
''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, ...
''. ''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
Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder characterized by a group of symptoms that commonly include abdominal pain, abdominal bloating, and changes in the consistency of bowel movements. These symptoms may ...
.
Signs and symptoms
Researchers have published conflicting reports concerning whether ''Blastocystis'' causes symptoms in humans, with one of the earliest reports in 1916.
The incidence of reports associated with symptoms began to increase in 1984,
with physicians from Saudi Arabia reporting symptoms in humans
and US physicians reporting symptoms in individuals with travel to less developed countries.
A lively debate ensued in the early 1990s, with some physicians objecting to publication of reports that ''Blastocystis'' caused disease.
Some researchers believe the debate has been resolved by finding of multiple species of ''Blastocystis'' that can infect humans, with some causing symptoms and others being harmless (see Genetics and Symptoms).
A few of most commonly reported symptoms are:
* abdominal pain
*
itching
An itch (also known as pruritus) is a sensation that causes a strong desire or reflex to scratch. Itches have resisted many attempts to be classified as any one type of sensory experience. Itches have many similarities to pain, and while both ...
, usually
anal itching
* constipation
* diarrhea
* watery or loose stools
* weight loss
* fatigue
* flatulence
Some less commonly reported symptoms include:
* Skin rash
* Arthritic symptoms and joint pain
* Intestinal inflammation
Variation in severity
Researchers have sought to develop models to understand the variety of symptoms seen in humans. Some patients do not have symptoms, while others report severe diarrhea and fatigue.
A number of researchers have investigated the possibility that some species of ''Blastocystis'' are more virulent than others. An Italian researcher reported differences in the protein profiles of isolates associated with chronic and acute infection.
A research team from Malaysia reported that isolates from symptomatic patients produced large amoeboid forms that were not present in isolates from asymptomatic patients.
The development of a classification system for ''Blastocystis'' in 2007 produced a series of studies investigating this possibility.
The studies that followed generally found that no specific "pathogenic" or nonpathogenic species of ''Blastocystis'' exists.
One study investigated the subtypes found in patients with irritable bowel syndrome (IBS),
inflammatory bowel disease
Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine, with Crohn's disease and ulcerative colitis (UC) being the principal types. Crohn's disease affects the small intestine and large intestine ...
(IBD), and chronic diarrhea, and found the subtypes in these diseases were similar (subtypes 2 and 3), and have also been found in asymptomatic carriers. The researchers concluded that host factors, such as age and genetics, may play the dominant role in determining the symptoms seen in the disease.
Associations
Blastocystis colonisation is positively associated with
IBS and is a possible risk factor for developing IBS.
A study of IBS patients in the Middle East showed a "significantly increased" immune reaction in IBS patients to ''Blastocystis'', even when the organism could not be identified in stool samples.
The following reports have linked ''Blastocystis'' infection to
inflammatory bowel disease
Inflammatory bowel disease (IBD) is a group of inflammatory conditions of the colon and small intestine, with Crohn's disease and ulcerative colitis (UC) being the principal types. Crohn's disease affects the small intestine and large intestine ...
:
* A study using riboprinting identified specific types of ''Blastocystis'' as associated with inflammation.
* A case report described IBD in conjunction with ''Blastocystis'' infection.
* Three research groups have reported experimental infection of mice with ''Blastocystis'' produces intestinal inflammation.
Transmission and risk factors
Humans contract ''Blastocystis'' infection by drinking water or eating food contaminated with
feces
Feces (also known as faeces American and British English spelling differences#ae and oe, or fæces; : faex) are the solid or semi-solid remains of food that was not digested in the small intestine, and has been broken down by bacteria in the ...
from an infected human or animal.
[
] ''Blastocystis'' infection can be spread from animals to humans, from humans to other humans, from humans to animals, and from animals to animals.
Risk factors for infection have been reported as following:
* International travel: Travel to less developed countries has been cited in development of symptomatic Blastocystis infection.
A 1986 study in the United States found that all individuals symptomatically infected with ''Blastocystis'' reported recent travel history to less developed countries.
In the same study, all hospital employees working in New York who were screened for ''Blastocystis'' were found to have asymptomatic infections.
* Military service: Several studies have identified high rates of infection in military personnel. An early account described infection of British troops in Egypt in 1916
who recovered following treatment with
emetine. A 1990 study published in ''
Military Medicine'' from Lackland AFB in Texas concluded symptomatic infection was more common in foreign nationals, children, and immunocompromised individuals.
A 2002 study published in ''Military Medicine'' of army personnel in
Thailand
Thailand, officially the Kingdom of Thailand and historically known as Siam (the official name until 1939), is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. With a population of almost 66 million, it spa ...
identified a 44% infection rate. Infection rates were highest in privates who had served the longest at the army base.
A follow-up study found a significant correlation between infection and symptoms, and identified the most likely cause as contaminated water.
A 2007 newspaper article suggested the infection rate of US military personnel returning from the Gulf War was 50%, quoting the head of
Oregon State University
Oregon State University (OSU) is a Public university, public Land-grant university, land-grant research university in Corvallis, Oregon, United States. OSU offers more than 200 undergraduate degree programs and a variety of graduate and doctor ...
's Biomedicine department.
* Consumption of Untreated Water (well water): Many studies have linked ''Blastocystis'' infection with contaminated drinking water. A 1993 study of children infected symptomatically with ''Blastocystis'' in Pittsburgh indicated that 75% of them had a history of drinking well water or travel in less developed countries. Two studies in Thailand linked ''Blastocystis'' infection in military personnel and families to drinking of unboiled and untreated water.
A book published in 2006 noted that in an
Oregon
Oregon ( , ) is a U.S. state, state in the Pacific Northwest region of the United States. It is a part of the Western U.S., with the Columbia River delineating much of Oregon's northern boundary with Washington (state), Washington, while t ...
community, infections are more common in winter months during heavy rains.
A research study published in 1980 reported bacterial contamination of well water in the same community during heavy rainfall.
A 2007 study from China specifically linked infection with ''Blastocystis sp. subtype 3'' with drinking untreated water.
Recreational contact with untreated water, for example through boating, has also been identified as a risk factor.
Studies have shown that ''Blastocystis'' survives sewage treatment plants in both the United Kingdom and Malaysia.
[
] ''Blastocystis'' cysts have been shown to be resistant to chlorination as a treatment method
and are among the most resistant cysts to ozone treatment.
* Contaminated Food: Contamination of leafy vegetables has been implicated as a potential source for transmission of ''Blastocystis'' infection, as well as other gastrointestinal protozoa.
[
] A Chinese study identified infection with ''Blastocystis sp. subtype 1'' as specifically associated with eating foods grown in untreated water.
[
]
* Daycare facilities: A Canadian study identified an outbreak of ''Blastocystis'' associated with daycare attendance.
Prior studies have identified outbreaks of similar protozoal infections in daycares.
* Geography: Infection rates vary geographically, and variants which produce symptoms may be less common in industrialized countries. For example, a low incidence of ''Blastocystis'' infection has been reported in Japan.
A study of individuals infected with ''Blastocystis'' in Japan found that many (43%, 23/54) carried ''Blastocystis sp. subtype 2'', which was found to produce no symptoms in 93% (21/23) of patients studied, in contrast to other variants which were less common but produced symptoms in 50% of Japanese individuals. Studies in urban areas of industrialized countries have found ''Blastocystis'' infection associated with a low incidence of symptoms.
In contrast, studies in developing countries generally show ''Blastocystis'' to be associated with symptoms.
In the United States, a higher incidence of ''Blastocystis'' infection has been reported in California and West Coast states.
* Prevalence over Time: A 1989 study of the prevalence of ''Blastocystis'' in the United States found an infection rate of 2.6% in samples submitted from all 48 states.
The study was part of the
CDC
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency under the Department of Health and Human Services (HHS), and is headquartered in Atlanta, ...
's
MMWR Report. A more recent study, in 2006, found an infection rate of 23% in samples submitted from all 48 states. However, the more recent study was performed by a private laboratory located in the Western US, and emphasized samples from Western states, which have previously been reported to have a higher infection rate.
Research studies have suggested the following items are not risk factors for contracting ''Blastocystis'' infection:
* Consumption of municipal water near water plant (not a risk factor): One study showed that municipal water was free of ''Blastocystis'', even when drawn from a polluted source. However, samples taken far away from the treatment plant showed cysts. The researchers suggested that aging pipes may permit intrusion of contaminated water into the distribution system.
* Human-to-Human transmission among adults (not a risk factor): Some research suggests that direct human-to-human transmission is less common even in households and between married partners. One study showed different members of the same household carried different subtypes of Blastocystis.
Pathogeneses
Pathogenesis refers to the mechanism by which an organism causes disease. The following disease-causing mechanisms have been reported in studies of ''Blastocystis'' infection:
* Barrier disruption: In isolates from ''Blastocystis sp. subtype 4'', study has demonstrated that ''Blastocystis'' has the ability to alter the arrangement of F-actin in intestinal
epithelial cells
Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...
.
Actin filaments
Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other p ...
are important in stabilizing
tight junctions
Tight junctions, also known as occluding junctions or ''zonulae occludentes'' (singular, ''zonula occludens''), are multiprotein junctional complexes between epithelial cells, sealing and preventing leakage of solutes and water. They also play a ...
; they in turn stabilize the barrier, which is a layer of cells, between the intestinal epithelial cells and the intestinal content.
The parasite causes the actin filaments to rearrange, and so compromising barrier function. This has been suggested to contribute to the diarrheal symptoms sometimes observed in ''Blastocystis'' patients.
* Invasiveness: Invasive infection has been reported in humans
and animal studies.
* Immune modulation: ''Blastocystis'' has been shown to provoke cells from the human colon to produce inflammatory
cytokines
Cytokines () are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling.
Cytokines are produced by a broad range of cells, including immune cells like macrophages, B cell, B lymphocytes, T cell, T lymphocytes ...
interleukin-8
Interleukin 8 (IL-8 or chemokine (C-X-C motif) ligand 8, CXCL8) is a chemokine produced by macrophages and other cell types such as epithelial cells, airway smooth muscle cells and endothelial cells. Endothelial cells store IL-8 in their storage ...
and
GM-CSF.
Interleukin-8
Interleukin 8 (IL-8 or chemokine (C-X-C motif) ligand 8, CXCL8) is a chemokine produced by macrophages and other cell types such as epithelial cells, airway smooth muscle cells and endothelial cells. Endothelial cells store IL-8 in their storage ...
plays a role in rheumatoid arthritis.
* Protease secretion: ''Blastocystis'' secretes a
protease
A protease (also called a peptidase, proteinase, or proteolytic enzyme) is an enzyme that catalysis, catalyzes proteolysis, breaking down proteins into smaller polypeptides or single amino acids, and spurring the formation of new protein products ...
that breaks up antibodies produced and secreted into the
gastrointestinal tract
The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...
lumen.
These antibodies, known as
immunoglobulin A (IgA), make up the
immune defense system of human by preventing the growth of harmful microorganisms in the body and by neutralizing
toxin
A toxin is a naturally occurring poison produced by metabolic activities of living cells or organisms. They occur especially as proteins, often conjugated. The term was first used by organic chemist Ludwig Brieger (1849–1919), derived ...
s secreted by these microorganisms. By breaking up the antibodies, it allows the persistence of ''Blastocystis'' in the human gut. Another more recent study has also shown and proposed that, in response to the proteases secreted by ''Blastocystis'', the intestinal
host cells would signal a series of events to be carried out, eventually leading to the self-destruction of the host cells – a phenomenon known as
apoptosis
Apoptosis (from ) is a form of programmed cell death that occurs in multicellular organisms and in some eukaryotic, single-celled microorganisms such as yeast. Biochemistry, Biochemical events lead to characteristic cell changes (Morphology (biol ...
.
* Other secretory mechanism: A study of a different protozoan which produces similar symptoms, ''
Entamoeba histolytica
''Entamoeba histolytica'' is an anaerobic organism, 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 mil ...
'', found that organism secretes several neurologically active chemicals, such as
serotonin
Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...
and
Substance P
Substance P (SP) is an undecapeptide (a peptide composed of a chain of 11 amino acid residues) and a type of neuropeptide, belonging to the tachykinin family of neuropeptides. It acts as a neurotransmitter and a neuromodulator. Substance P ...
.
Serum levels of
serotonin
Serotonin (), also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter with a wide range of functions in both the central nervous system (CNS) and also peripheral tissues. It is involved in mood, cognition, reward, learning, ...
have been found to be elevated in patients with ''
Entamoeba histolytica
''Entamoeba histolytica'' is an anaerobic organism, 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 mil ...
''.
Diagnosis
Clinically available
Diagnosis is performed by determining if the infection is present, and then making a decision as to whether the infection is responsible for the symptoms. Diagnostic methods in clinical use have been reported to be of poor quality and more reliable methods have been reported in research papers.

For identification of infection, the only method clinically available in most areas is the ova and parasite (O&P) exam, which identifies the presence of the organism by microscopic examination of a chemically preserved stool specimen. This method is sometimes called direct microscopy. In the United States, pathologists are required to report the presence of ''Blastocystis'' when found during an O&P exam, so a special test does not have to be ordered. Direct microscopy is inexpensive, as the same test can identify a variety of gastrointestinal infections, such as ''
Giardia
''Giardia'' ( or ) 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 be ...
'', ''
Entamoeba histolytica
''Entamoeba histolytica'' is an anaerobic organism, 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 mil ...
'', and ''
Cryptosporidium
''Cryptosporidium'', sometimes called crypto, is an apicomplexan genus of alveolates which are parasitism, parasites that can cause a respiratory and gastrointestinal illness (cryptosporidiosis) that primarily involves watery diarrhea (inte ...
''. However, one laboratory director noted that pathologists using conventional microscopes failed to identify many ''Blastocystis'' infections, and indicated the necessity for special microscopic equipment for identification.
The following table shows the sensitivity of Direct Microscopy in detecting ''Blastocystis'' when compared to stool culture, a more sensitive technique. Stool culture was considered by some researchers to be the most reliable technique, but a recent study found stool culture only detected 83% of individuals infected when compared to
polymerase chain reaction
The polymerase chain reaction (PCR) is a method widely used to make millions to billions of copies of a specific DNA sample rapidly, allowing scientists to amplify a very small sample of DNA (or a part of it) sufficiently to enable detailed st ...
(PCR) testing.
Reasons given for the failure of Direct Microscopy include: (1) Variable Shedding: The quantity of ''Blastocystis'' organisms varies substantially from day to day in infected humans and animals;
(2) Appearance: Some forms of ''Blastocystis'' resemble fat cells or white blood cells,
making it difficult to distinguish the organism from other cells in the stool sample; (3) Large number of morphological forms: ''Blastocystis'' cells can assume a variety of shapes, some have been described in detail only recently, so it is possible that additional forms exist but have not been identified.
Several methods have been cited in literature for determination of the significance of the finding of ''Blastocystis'':
# Diagnosis only when large numbers of organism present: Some physicians consider ''Blastocystis'' infection to be a cause of illness only when large numbers are found in stool samples.
Researchers have questioned this approach, noting that it is not used with any other protozoal infections, such as ''Giardia'' or ''Entamoeba histolytica''. Some researchers have reported no correlation between number of organisms present in stool samples and the level of symptoms.
A study using polymerase chain reaction testing of stool samples suggested that symptomatic infection can exist even when sufficient quantities of the organism do not exist for identification through Direct Microscopy.
# Diagnosis-by-exclusion: Some physicians diagnose ''Blastocystis'' infection by excluding all other causes, such as infection with other organisms, food intolerances, colon cancer, etc. This method can be time-consuming and expensive, requiring many tests such as
endoscopy
An endoscopy is a procedure used in medicine to look inside the body. The endoscopy procedure uses an endoscope to examine the interior of a hollow organ or cavity of the body. Unlike many other medical imaging techniques, endoscopes are insert ...
and
colonoscopy
Colonoscopy () or coloscopy () is a medical procedure involving the Endoscopy, endoscopic examination of the large bowel (colon) and the distal portion of the small bowel. This examination is performed using either a Charge-coupled device, CCD ...
.
# Disregarding ''Blastocystis'' : In the early to mid-1990s, some US physicians suggested all findings of ''Blastocystis'' are insignificant. No recent publications expressing this opinion could be found.
Not clinically available
The following diagnostic methods are not routinely available to patients. Researchers have reported that they are more reliable at detecting infection, and in some cases can provide the physician with information to help determine whether ''Blastocystis'' infection is the cause of the patient's symptoms:
Serum antibody testing: A 1993 research study performed by the
NIH with United States patients suggested that it was possible to distinguish symptomatic and asymptomatic infection with ''Blastocystis'' using serum antibody testing.
The study used blood samples to measure the patient's immune reaction to chemicals present on the surface of the ''Blastocystis'' cell. It found that patients diagnosed with symptomatic ''Blastocystis'' infection exhibited a much higher immune response than controls who had ''Blastocystis'' infection but no symptoms. The study was repeated in 2003 at
Ain Shams University
Ain Shams University () is a public university located in Cairo, Egypt. Founded in 1950, the university provides education at the undergraduate, graduate and post-graduate levels.
History
Ain Shams University was founded in July 1950, the third ...
in Egypt with Egyptian patients with equivalent results.
Fecal antibody testing: A 2003 study at Ain Shams University in Egypt indicated that patients symptomatically infected could be distinguished with a fecal antibody test.
The study compared patients diagnosed with symptomatic ''Blastocystis'' infection to controls who had ''Blastocystis'' infection but no symptoms. In the group with symptoms, IgA antibodies to ''Blastocystis'' were detected in fecal specimens that were not present in the healthy control group.
Stool culture: Culturing has been shown to be a more reliable method of identifying infection. In 2006, researchers reported the ability to distinguish between disease causing and non-disease causing isolates of ''Blastocystis'' using stool culture.
''Blastocystis'' cultured from patients who were sick and diagnosed with ''Blastocystis'' infection produced large, highly adhesive amoeboid forms in culture. These cells were absent in ''Blastocystis'' cultures from healthy controls. Subsequent genetic analysis showed the ''Blastocystis'' from healthy controls was genetically distinct from that found in patients with symptoms. Protozoal culture is unavailable in most countries due to the cost and lack of trained staff able to perform protozoal culture.
Genetic analysis of isolates: Researchers have used techniques which allow the DNA of ''Blastocystis'' to be isolated from fecal specimens.
This method has been reported to be more reliable at detecting ''Blastocystis'' in symptomatic patients than stool culture.
This method also allows the species group of ''Blastocystis'' to be identified. Research is continuing into which species groups are associated with symptomatic (see Genetics and Symptoms) blastocystosis.
Immuno-fluorescence (IFA) stain: An IFA stain causes ''Blastocystis'' cells to glow when viewed under a microscope, making the diagnostic method more reliable. IFA stains are in use for
Giardia
''Giardia'' ( or ) 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 be ...
and
Cryptosporidium
''Cryptosporidium'', sometimes called crypto, is an apicomplexan genus of alveolates which are parasitism, parasites that can cause a respiratory and gastrointestinal illness (cryptosporidiosis) that primarily involves watery diarrhea (inte ...
for both diagnostic purposes and water quality testing. A 1991 paper from the
NIH described the laboratory development of one such stain.
However, no company currently offers this stain commercially.
Classification
Reports conflict regarding whether ''Blastocystis'' causes disease in humans. These reports resulted in a brief debate in medical journals in the early 1990s between some physicians in the United States who believed that ''Blastocystis'' was harmless, and physicians in the United States and overseas who believed it could cause disease.
At the time, it was common practice to identify all ''Blastocystis'' from humans as ''
Blastocystis hominis
''Blastocystis hominis'' is a single-celled Eukaryote, eukaryotic organism that inhabits the gastrointestinal tract of humans and various animals. This stramenopile exhibits significant genetic diversity and has become an organism of increasing s ...
'', while ''Blastocystis'' from animals was identified differently (e.g. ''Blastocystis ratti'' from rats). Research performed since then has shown that the concept of ''Blastocystis hominis'' as a unique species of ''Blastocystis'' infecting humans is not supported by microbiological findings. Although one species group associated with primates was found, it was also discovered that humans can acquire infection from any one of nine species groups of ''Blastocystis'' which are also carried by cattle, pigs, rodents, chickens, pheasants, monkeys, dogs, and other animals.
Research has suggested that some types produce few or no symptoms, while others produce illness and intestinal inflammation.
Researchers have suggested conflicting reports may be due to the practice of naming all ''Blastocystis'' from humans ''Blastocystis hominis''
and have proposed discontinuing the use of that term.
A standard naming system for ''Blastocystis'' organisms from humans and animals has been proposed which names ''Blastocystis'' isolates according to the genetic identity of the ''Blastocystis'' organism rather than the host.
The naming system used identifies all isolates as ''Blastocystis'' sp. subtype ''nn'' where nn is a number from 1 to 9 indicating the species group of the ''Blastocystis'' organism. The identification of the species can not be performed with a microscope at this time, because the different species look alike. Identification requires equipment for genetic analysis that is common in microbiology laboratories, but not available to most physicians. Some new scientific papers have begun using the standard naming system.
Treatment
There is a lack of scientific study to support the efficacy of any particular treatment.
An additional review published in 2009 made a similar conclusion, noting that because the diagnostics in use have been unreliable, it has been impossible to determine whether a drug has eradicated the infection, or just made the patient feel better.
Historical reports, such as one from 1916, note difficulty associated with eradication of ''Blastocystis'' from patients, describing it as "an infection that is hard to get rid of."
A 1999 ''in vitro'' study from Pakistan found 40% of isolates are resistant to common antiprotozoal drugs.
A study of isolates from patients diagnosed with IBS found 40% of isolates resistant to
metronidazole
Metronidazole, sold under the brand name Flagyl and Metrogyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vagino ...
and 32% resistant to
furazolidone.
Drugs reported in studies to be effective in eradicating ''Blastocystis'' infection have included
metronidazole
Metronidazole, sold under the brand name Flagyl and Metrogyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vagino ...
,
trimethoprim
Trimethoprim (TMP) is an antibiotic used mainly in the treatment of bladder infections. Other uses include for middle ear infections and travelers' diarrhea. With sulfamethoxazole or dapsone it may be used for ''Pneumocystis'' pneumonia ...
,
TMP-SMX (only trimethoprim is active with
sulphamethoxazole demonstrating no activity),
tetracycline
Tetracycline, sold under various brand names, is an antibiotic in the tetracyclines family of medications, used to treat a number of infections, including acne, cholera, brucellosis, plague, malaria, and syphilis. It is available in oral an ...
,
doxycycline
Doxycycline is a Broad-spectrum antibiotic, broad-spectrum antibiotic of the Tetracycline antibiotics, tetracycline class used in the treatment of infections caused by bacteria and certain parasites. It is used to treat pneumonia, bacterial p ...
,
nitazoxanide
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 ...
,
pentamidine
Pentamidine is an antimicrobial medication used to treat African trypanosomiasis, leishmaniasis, '' Balamuthia'' infections, babesiosis, and to prevent and treat pneumocystis pneumonia (PCP) in people with poor immune function. In African trypa ...
,
paromomycin and
iodoquinol.
Iodoquinol has been found to be less effective in practice than in-vitro.
Miconazole
Miconazole, sold under the brand name Monistat among others, is an antifungal medication used to treat ring worm, pityriasis versicolor, and yeast infections of the skin or vagina. It is used for ring worm of the body, groin (jock itch), a ...
and
quinacrine
Mepacrine, also called quinacrine or by the trade names Atabrine or Atebrin, is a medication with several uses. It is related to chloroquine and mefloquine. Although available from compounding pharmacies, as of August 2020 approved formulation ...
have been reported as effective agents against ''Blastocystis'' growth in-vitro.
Rifaximin
Rifaximin is a non-absorbable, broad-spectrum antibiotic mainly used to treat travelers' diarrhea. It is based on the rifamycin antibiotics family. Since its approval in Italy in 1987, it has been licensed in more than 30 countries for the t ...
,
and
albendazole
Albendazole is a broad-spectrum antihelmintic and antiprotozoal agent of the benzimidazole type. It is used for the treatment of a variety of intestinal parasite infections, including ascariasis, pinworm infection, hookworm infection, trichuri ...
have shown promise as has
ivermectin
Ivermectin is an antiparasitic drug. After its discovery in 1975, its first uses were in veterinary medicine to prevent and treat heartworm and acariasis. Approved for human use in 1987, it is used to treat infestations including head lice ...
which demonstrated high effectiveness against blastocystis hominis isolates in an in vitro study.
There is also evidence that the probiotic yeast ''
Saccharomyces boulardii'',
and the plant ''
Mallotus oppositifolius''
may be effective against ''Blastocystis'' infections.
Physicians have described the successful use of a variety of discontinued antiprotozoals in treatment of ''Blastocystis'' infection.
Emetine was reported as successful in cases in early 20th century with British soldiers who contracted ''Blastocystis'' infection while serving in Egypt.
''In vitro'' testing showed
emetine was more effective than
metronidazole
Metronidazole, sold under the brand name Flagyl and Metrogyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vagino ...
or
furazolidone.
Emetine is available in the United States through special arrangement with the
Center for Disease Control
The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency under the Department of Health and Human Services (HHS), and is headquartered in Atlanta, ...
.
Clioquinol (Entero-vioform) was noted as successful in treatment of ''Blastocystis'' infection but removed from the market following an adverse event in Japan.
Stovarsol and Narsenol, two arsenic-based antiprotozoals, were reported to be effective against the infection.
Carbarsone was available as an anti-infective compound in the United States as late as 1991, and was suggested as a possible treatment.
The reduction in the availability of antiprotozoal drugs has been noted as a complicating factor in treatment of other protozoal infections.
For example, in
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
, production of
diloxanide furoate ended in 2003,
paromomycin is available under special access provisions, and the availability of
iodoquinol is limited.
Epidemiology

Like other protozoal infections, the prevalence of ''Blastocystis'' infection varies depending on the area investigated and the population selected. A number of different species groups of ''Blastocystis'' infect humans,
with some being reported to cause disease while others do not.
To date, surveys have not distinguished between different types of ''Blastocystis'' in humans, so the significance of findings may be difficult to evaluate. Developing countries have been reported to have higher incidences, but recent studies suggest that symptomatic infection with ''Blastocystis'' may be prevalent in certain industrialized countries, as well.
* A study on parasites in stool samples in the United States during 2000 found blastocystosis to be the most common parasitic infection in the population, occurring in 23% of individuals.
[Figure 4: Prevalence of IBS and Blastocystosis by country]
/ref>
* A Canadian study of samples received in 2005 identified ''Blastocystis'' as the most prevalent protozoal infection identified.
* A study in Pakistan identified ''Blastocystis'' infection in 7% of the general population and 46% of patients with irritable bowel syndrome. The study used stool culture for identification.
* A 2014 study of samples from 93 children from the Senegal River
The Senegal River ( or "Senegal" - compound of the Serer term "Seen" or "Sene" or "Sen" (from Roog Seen, Supreme Deity in Serer religion) and "O Gal" (meaning "body of water")); , , , ) is a river in West Africa; much of its length mark ...
basin found that 100% of the population was infected with ''Blastocystis''.[Table 2: Summary of treatments and efficacy for Blastocystis infection]
Other animals
Experimental infection in immunocompetent and immunocompromised mice has produced intestinal inflammation, altered bowel habits, lethargy, and death. Chronic diarrhea has been reported in non-human higher primates.
Research
While many enteric protists are the subject of research, ''Blastocystis'' is unusual in that basic questions concerning how it should be diagnosed and treated and how it causes disease remain unsettled. The following groups have ongoing research programs directed at these questions:
See also
* Blastocystis
''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, ...
* List of parasites (human)
* History of emerging infectious diseases
References
External links
CDC description of ''Blastocystis hominis''
{{Gastroenterology
Protozoal diseases
Waterborne diseases
Conditions diagnosed by stool test
Abdominal pain