|Classification and external resources|
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.
Physicians have produced conflicting reports 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, while Blastocystis from animals was identified differently (i.e. 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 producing 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.
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).
The most commonly reported symptoms are:
- abdominal pain
- weight loss
Less commonly reported symptoms are:
- 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 there is no specific "pathogenic" or non-pathogenic species of Blastocystis. One study investigated the subtypes found in patients with irritable bowel syndrome (IBS), inflammatory bowel disease (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.
The following reports have linked Blastocystis infection to Irritable bowel syndrome:
- A study of IBS patients in the Middle East found 46% were infected with Blastocystis vs. 7% of healthy controls.
- An additional 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.
- A European study compared Blastocystis infection rates in IBS patients to those of healthy controls and found a statistically significant infection rate in IBS patients.
- Early reports from the US physicians in the 1980s suggested the presence of the organism was not relevant to the diagnostic process, and patients infected with Blastocystis could be diagnosed with IBS.
The following reports have linked Blastocystis infection to inflammatory bowel disease:
- A study using riboprinting identified specific types of Blastocystis as associated with inflammation.
- A case report described inflammatory bowel disease in conjunction with Blastocystis infection.
- Three research groups have reported experimental infection of mice with Blastocystis produces intestinal inflammation.
- An article in a non-peer reviewed medical journal noted that the increase in Blastocystis case reports coincided with reported increases in the prevalence of inflammatory bowel disease from several European countries.
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, Entamoeba histolytica, Cryptosporidium. 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 (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 and colonoscopy.
- 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 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 and Cryptosporidium 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.
Transmission and risk factors
Humans contract Blastocystis infection by drinking water or eating food contaminated with feces 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 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'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 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 though 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'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.
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. Actin filaments are important in stabilizing tight junctions; 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.
- Immune Modulation: Blastocystis has been shown to provoke cells from the human colon to produce inflammatory cytokines Interleukin-8 and GM-CSF. Interleukin-8 plays a role in rheumatoid arthritis.
- Protease Secretion: Blastocystis secretes a protease that breaks up antibodies produced and secreted into the gastrointestinal tract 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 toxins 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.
- Other secretory mechanism: A study of a different protozoan which produces similar symptoms, Entamoeba histolytica, found that organism secretes several neurologically active chemicals, such as serotonin and Substance P. Serum levels of serotonin have been found to be elevated in patients with Entamoeba histolytica. One paper noted the diffuse symptoms of Blastocystis infection correlate with serotonin's role in the body, and suggested a similar mechanism may be present in Blastocystis infection.
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 from Pakistan study 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 and 32% resistant to furazolidone. Drugs reported in studies have included Metronidazole, TMP-SMX, Doxycycline, Nitazoxanide Iodoquinol and Paromomycin. Iodoquinol has been found to be less effective in practice and in-vitro. Miconazole has been reported as an agent against Blastocystis growth in-vitro.
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 or furazolidone. Emetine is available in the United States through special arrangement with the Center for Disease Control. 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, production of diloxanide furoate ended in 2003, paromomycin is available under special access provisions, and the availability of iodoquinol is limited.
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, however recent studies suggest that symptomatic infection with Blastocystis may be prevalent in certain areas of industrialized countries as well:
- A nation-wide study conducted by the CDC using data reported from 1987 found the prevalence Blastocystis infection in the United States to be 2.6%. The study indicated that Western states, such as California, reported a higher prevalence.
- A 2000 study by a private laboratory of stool samples from 48 states in the United States identified a prevalence of 23%. The study was conducted by a laboratory in Arizona and emphasized Western states which have previously been found to have higher rates of Blastocystis infection.
- 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.
In 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.
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:
|Country||Organization||Year Established||Research focus||Research|
|Singapore||National University of Singapore||1991||Co-culture, pathogenesis||Tan|
|Malaysia||University of Malaya||1996||Ultrastructure, pathogenicity||Kumar|
|United States||Blastocystis Research Foundation||2006||Phylogenetics, pathogenicity,
|Denmark||Statens Serum Institut||2006||Diagnostics||Stensvold|
- CDC description of Blastocystis hominis
- Blastocystis Research Foundation
- Badbugs.org: Dientamoeba fragilis and Blastocystis hominis resources
- Parkar U, Traub RJ, Kumar S et al. (2007). "Direct characterization of Blastocystis from faeces by PCR and evidence of zoonotic potential". Parasitology 134 (Pt 3): 359–67. doi:10.1017/S0031182006001582. PMID 17052374.
- Stensvold CR, Suresh GK, Tan KS et al. (2007). "Terminology for Blastocystis subtypes—a consensus". Trends Parasitol. 23 (3): 93–6. doi:10.1016/j.pt.2007.01.004. PMID 17241816.
- Noël C, Dufernez F, Gerbod D et al. (2005). "Molecular Phylogenies of Blastocystis Isolates from Different Hosts: Implications for Genetic Diversity, Identification of Species, and Zoonosis". J. Clin. Microbiol. 43 (1): 348–55. doi:10.1128/JCM.43.1.348-355.2005. PMC 540115. PMID 15634993.
- Tan TC, Suresh KG, Thong KL, Smith HV (2006). "PCR fingerprinting of Blastocystis isolated from symptomatic and asymptomatic human hosts". Parasitol. Res. 99 (4): 459–65. doi:10.1007/s00436-006-0177-0. PMID 16628457.
- Tan TC, Suresh KG (2006). "Predominance of amoeboid forms of Blastocystis hominis in isolates from symptomatic patients". Parasitol. Res. 98 (3): 189–93. doi:10.1007/s00436-005-0033-7. PMID 16323025.
- Menounos PG, Spanakos G, Tegos N, Vassalos CM, Papadopoulou C, Vakalis NC (2007). "Direct detection of Blastocystis sp. in human faecal samples and subtype assignment using single strand conformational polymorphism and sequencing". Molecular and Cellular Probes 22 (1): 24–9. doi:10.1016/j.mcp.2007.06.007. PMID 17669623.
- Low GC. (1916). "Two chronic amoebic dysentery carriers treated by emetine, with some remarks on the treatment of Lamblia, Blastocystis and E. coli infections". J. Trop. Med. Hyg. (19): 29–34.
- Zierdt CH (1991). "Blastocystis hominis--past and future". Clin. Microbiol. Rev. 4 (1): 61–79. PMC 358179. PMID 2004348.
- Qadri SM, al-Okaili GA, al-Dayel F (1989). "Clinical significance of Blastocystis hominis". J. Clin. Microbiol. 27 (11): 2407–9. PMC 267045. PMID 2808664.
- Sheehan DJ, Raucher BG, McKitrick JC (1986). "Association of Blastocystis hominis with signs and symptoms of human disease". J. Clin. Microbiol. 24 (4): 548–50. PMC 268968. PMID 3771743.
- Markell EK, Udkow MP (1990). "Association of Blastocystis hominis with human disease?". J. Clin. Microbiol. 28 (5): 1085–6. PMC 267874. PMID 2351728.
- Zierdt CH (1991). "Pathogenicity of Blastocystis hominis". J. Clin. Microbiol. 29 (3): 662–3. PMC 269843. PMID 2037690.
- Rosenblatt JE (1990). "Blastocystis hominis". J. Clin. Microbiol. 28 (10): 2379–80. PMC 268186. PMID 2101593.
- Lee MJ (1991). "Pathogenicity of Blastocystis hominis". J. Clin. Microbiol. 29 (9): 2089. PMC 270271. PMID 1774343.
- Gupta R, Parsi K (2006). "Chronic urticaria due to Blastocystis hominis". Australasian J. Dermatology. 47 (2): 117–9. doi:10.1111/j.1440-0960.2006.00244.x. PMID 16637808.
- Amin O. "The epidemiology of Blastocystis hominis in the United States". Research Journal of Parasitology 1 (1): 1–10.
- Biedermann T, Hartmann K, Sing A, Przybilla B (2002). "Hypersensitivity to non-steroidal anti-inflammatory drugs and chronic urticaria cured by treatment of Blastocystis hominis infection". Br. J. Dermatol. 146 (6): 1113–4. doi:10.1046/j.1365-2133.2002.473212.x. PMID 12072100.
- Pasqui AL, Savini E, Saletti M, Guzzo C, Puccetti L, Auteri A (2004). "Chronic urticaria and Blastocystis hominis infection: a case report". European Review for Medical and Pharmacological Sciences 8 (3): 117–20. PMID 15368795.
- Valsecchi R, Leghissa P, Greco V (2004). "Cutaneous lesions in Blastocystis hominis infection". Acta Derm. Venereol. 84 (4): 322–3. doi:10.1080/00015550410025949. PMID 15339085.
- Micheloud D, Jensen J, Fernandez-Cruz E, Carbone J (2007). "[Chronic angioedema and Blastocystis hominis infection]" [Chronic angioedema and Blastocystis hominis infection]. Revista de gastroenterología del Perú : órgano oficial de la Sociedad de Gastroenterología del Perú (in Spanish) 27 (2): 191–3. PMID 17712397.
- Krüger K, Kamilli I, Schattenkirchner M (1994). "[Blastocystis hominis as a rare arthritogenic pathogen. A case report]" [Blastocystis hominis as a rare arthritogenic pathogen. A case report]. Zeitschrift für Rheumatologie (in German) 53 (2): 83–5. PMID 8023590.
- Lee MG, Rawlins SC, Didier M, DeCeulaer K (1990). "Infective arthritis due to Blastocystis hominis". Ann. Rheum. Dis. 49 (3): 192–3. doi:10.1136/ard.49.3.192. PMC 1004021. PMID 2322029.
- Carrascosa M, Martínez J, Pérez-Castrillón JL (1996). "Hemorrhagic proctosigmoiditis and Blastocystis hominis infectioqar". Annals of Internal Medicine 124 (2): 278–9. doi:10.7326/0003-4819-124-2-199601150-00031. PMID 8534017.
- Lanuza MD, Carbajal JA, Villar J, Mir A, Borras R. (1999). "Soluble-protein and antigenic heterogeneity in axenic Blastocystis hominis isolates: pathogenic implications". Parasitol Res. 85 (2): 93–7. doi:10.1007/s004360050515. PMID 9934956.
- Dogruman-Al F, Yoshikawa H, Kustimur S, Balaban N (October 2009). "PCR-based subtyping of Blastocystis isolates from symptomatic and asymptomatic individuals in a major hospital in Ankara, Turkey". Parasitol. Res. 106 (1): 263–8. doi:10.1007/s00436-009-1658-8. PMID 19847459.
- Stensvold CR, Lewis HC, Hammerum AM et al. (November 2009). "Blastocystis: unravelling potential risk factors and clinical significance of a common but neglected parasite". Epidemiol. Infect. 137 (11): 1655–63. doi:10.1017/S0950268809002672. PMID 19393117.
- Dogruman-Al F, Kustimur S, Yoshikawa H et al. (August 2009). "Blastocystis subtypes in irritable bowel syndrome and inflammatory bowel disease in Ankara, Turkey". Mem. Inst. Oswaldo Cruz 104 (5): 724–7. doi:10.1590/S0074-02762009000500011. PMID 19820833.
- Yakoob J, Jafri W, Jafri N, Islam M, Asim Beg M (2004). "In vitro susceptibility of Blastocystis hominis isolated from patients with irritable bowel syndrome". Br. J. Biomed. Sci. 61 (2): 75–7. PMID 15250669.
- Hussain R, Jaferi W, Zuberi S et al. (1997). "Significantly increased IgG2 subclass antibody levels to Blastocystis hominis in patients with irritable bowel syndrome". Am. J. Trop. Med. Hyg. 56 (3): 301–6. PMID 9129532.
- Giacometti A, Cirioni O, Fiorentini A, Fortuna M, Scalise G (1999). "Irritable bowel syndrome in patients with Blastocystis hominis infection". Eur. J. Clin. Microbiol. Infect. Dis. 18 (6): 436–9. doi:10.1007/s100960050314. PMID 10442423.
- Markell EK, Udkow MP (1986). "Blastocystis hominis: pathogen or fellow traveler?". Am. J. Trop. Med. Hyg. 35 (5): 1023–6. PMID 3766850.
- Kaneda Y, Horiki N, Cheng XJ, Fujita Y, Maruyama M, Tachibana H (2001). "Ribodemes of Blastocystis hominis isolated in Japan". Am. J. Trop. Med. Hyg. 65 (4): 393–6. PMID 11693890.
- Yao FR, Qiao JY, Zhao Y, Zhang X, Yang JH, Li XQ (2005). "[Experimental infection of mice with Blastocystis hominis]" [Experimental infection of mice with Blastocystis hominis]. Zhongguo Ji Sheng Chong Xue Yu Ji Sheng Chong Bing Za Zhi (in Chinese) 23 (6): 444–8. PMID 16566218.
- Moe KT, Singh M, Howe J et al. (1997). "Experimental Blastocystis hominis infection in laboratory mice". Parasitol. Res. 83 (4): 319–25. doi:10.1007/s004360050256. PMID 9134552.
- Zhang HW, Li W, Yan QY, He LJ, Su YP (2006). "[Impact of Blastocystis hominis infection on ultrastructure of intestinal mucosa in mice]" [Impact of Blastocystis hominis infection on ultrastructure of intestinal mucosa in mice]. Zhongguo Ji Sheng Chong Xue Yu Ji Sheng Chong Bing Za Zhi (in Chinese) 24 (3): 187–91. PMID 17094618.
- Boorom KF (2007). "Is this recently characterized gastrointestinal pathogen responsible for rising rates of inflammatory bowel disease (IBD) and IBD associated autism in Europe and the United States in the 1990s?". Med. Hypotheses 69 (3): 652–9. doi:10.1016/j.mehy.2007.01.027. PMID 17382484.
- Mahmoud MS, Saleh WA (2003). "Secretory and humoral antibody responses to Blastocystis hominis in symptomatic and asymptomatic human infections". Journal of the Egyptian Society of Parasitology 33 (1): 13–30. PMID 12739797.
- Leelayoova S, Taamasri P, Rangsin R, Naaglor T, Thathaisong U, Mungthin M (2002). "In-vitro cultivation: a sensitive method for detecting Blastocystis hominis". Ann. Trop. Med. Parasitol. 96 (8): 803–7. doi:10.1179/000349802125002275. PMID 12625935.
- Suresh K, Smith H (2004). "Comparison of methods for detecting Blastocystis hominis". Eur. J. Clin. Microbiol. Infect. Dis. 23 (6): 509–11. doi:10.1007/s10096-004-1123-7. PMID 15168139.
- Stensvold R, Brillowska-Dabrowska A, Nielsen HV, Arendrup MC (2006). "Detection of Blastocystis hominis in unpreserved stool specimens by using polymerase chain reaction". J. Parasitol. 92 (5): 1081–7. doi:10.1645/GE-840R.1. PMID 17152954.
- Vennila GD, Suresh Kumar G, Khairul Anuar A et al. (1999). "Irregular shedding of Blastocystis hominis". Parasitol. Res. 85 (2): 162–4. doi:10.1007/s004360050528. PMID 9934969.
- El-Shazly AM, Abdel-Magied AA, El-Beshbishi SN, El-Nahas HA, Fouad MA, Monib MS (2005). "Blastocystis hominis among symptomatic and asymptomatic individuals in Talkha Center, Dakahlia Governorate, Egypt". Journal of the Egyptian Society of Parasitology 35 (2): 653–66. PMID 16083074.
- Doyle PW, Helgason MM, Mathias RG, Proctor EM (1990). "Epidemiology and pathogenicity of Blastocystis hominis". J. Clin. Microbiol. 28 (1): 116–21. PMC 269548. PMID 2298869.
- Markell EK (1995). "Is there any reason to continue treating Blastocystis infections?". Clin. Infect. Dis. 21 (1): 104–5. doi:10.1093/clinids/21.1.104. PMID 7578717.
- Zierdt CH, Nagy B (1993). "Antibody response to Blastocystis hominis infections". Ann. Intern. Med. 118 (12): 985–6. doi:10.7326/0003-4819-118-12-199306150-00018. PMID 8489119.
- Tan, K.S.W. (1986). "Blastocystis in humans and animals: new insights using modern methodologies". Vet. Parasitol. 126 (1–2): 121–144. doi:10.1016/j.vetpar.2004.09.017. PMID 15567582.
- Sohail MR, Fischer PR (2005). "Blastocystis hominis and travelers". Travel medicine and infectious disease 3 (1): 33–8. doi:10.1016/j.tmaid.2004.06.001. PMID 17292002.
- Wenyon CM, O'Connor FW (1917). "An inquiry into some problems affecting the spread and incidence of intestinal protozoal infections of British troops and natives in Egypt, with special reference to the carrier question, diagnosis and treatment of amoebic dysentery, and an account of three new human intestinal protozoa". J. R. Army Med. Corps 28: 346–67.
- Wilson KW, Winget D, Wilks S (1990). "Blastocystis hominis infection: signs and symptoms in patients at Wilford Hall Medical Center". Military medicine 155 (9): 394–6. PMID 2120622.
- Leelayoova S, Rangsin R, Taamasri P, Naaglor T, Thathaisong U, Mungthin M (2004). "Evidence of waterborne transmission of Blastocystis hominis". Am. J. Trop. Med. Hyg. 70 (6): 658–62. PMID 15211009.
- Hogue, Theresa (January 14, 2007). "Parasite blamed for growing number of stomach disorders". Corvallis Gazette-Times. Retrieved 2007-08-08.
- Taamasri P, Mungthin M, Rangsin R, Tongupprakarn B, Areekul W, Leelayoova S (2000). "Transmission of intestinal blastocystosis related to the quality of drinking water". Southeast Asian J. Trop. Med. Public Health 31 (1): 112–7. PMID 11023076.
- Boorom, K (2006). Commensal and Pathogenic Blastocystis with Case Studies from Oregon's Willamette Valley. FBH Press. p. 112. ISBN 978-1-4303-0904-8.
- Lamka KG, LeChevallier MW, Seidler RJ. (1980). Bacterial contamination of drinking water supplies in a modern rural neighborhood. Appl Environ Microbiol. 39 (4). pp. 734–8. PMID 7377773.
- Li LH, Zhou XN, Du ZW et al. (2007). "Molecular epidemiology of human Blastocystis in a village in Yunnan province, China". Parasitology International 56 (4): 281–6. doi:10.1016/j.parint.2007.06.001. PMID 17627869.
- Utzinger J, Wu Z, Chen JX, Chen SH, Zhang L. (2005). "Viable Blastocystis Cysts in Scottish and Malaysian Sewage Samples". Appl Environ Microbiol. 71 (9): 5619–20. doi:10.1128/AEM.71.9.5619-5620.2005. PMC 1214661. PMID 16151162.
- Zaki M, Zaman V, Sheikh NA (1996). "Resistance of Blastocystis hominis cysts to chlorine". JPMA. the Journal of the Pakistan Medical Association 46 (8): 178–9. PMID 8936976.
- Khalifa AM, El Temsahy MM, Abou El Naga IF (2001). "Effect of ozone on the viability of some protozoa in drinking water". Journal of the Egyptian Society of Parasitology 31 (2): 603–16. PMID 11478459.
- Al-Binali AM, Bello CS, El-Shewy K, Abdulla SE. (2006). "The prevalence of parasites in commonly used leafy vegetables in South Western, Saudi Arabia". Saudi Med J. 27 (5): 613–6. PMID 16680247.
- Koutsavlis AT, Valiquette L, Allard R, Soto J (2001). "Blastocystis hominis: a new pathogen in day-care centres?" [Blastocystis hominis: a new pathogen in day-care centres?]. Can. Commun. Dis. Rep. (in French) 27 (9): 76–84. PMID 11381629.
- Skeels MR, Sokolow R, Hubbard CV, Andrus JK, Baisch J. (1990). "Cryptosporidium infection in Oregon public health clinic patients 1985-88: the value of statewide laboratory surveillance". Am J Public Health. 80 (3): 305–8. doi:10.2105/AJPH.80.3.305. PMC 1404665. PMID 2305910.
- Hirata T, Nakamura H, Kinjo N et al. (2007). "Prevalence of Blastocystis hominis and Strongyloides stercoralis infection in Okinawa, Japan". Parasitology Research 101 (6): 1717–9. doi:10.1007/s00436-007-0712-7. PMID 17717704.
- Leder K, Hellard ME, Sinclair MI, Fairley CK, Wolfe R (2005). "No correlation between clinical symptoms and Blastocystis hominis in immunocompetent individuals". J. Gastroenterol. Hepatol. 20 (9): 1390–4. doi:10.1111/j.1440-1746.2005.03868.x. PMID 16105126.
- Nimri LF (1993). "Evidence of an epidemic of Blastocystis hominis infections in preschool children in northern Jordan". J. Clin. Microbiol. 31 (10): 2706–8. PMC 265984. PMID 8253970.
- Kappus KK, Juranek DD, Roberts JM (1991). "Results of testing for intestinal parasites by state diagnostic laboratories, United States, 1987". MMWR. CDC surveillance summaries : Morbidity and mortality weekly report. CDC surveillance summaries / Centers for Disease Control 40 (4): 25–45. PMID 1779956.
- Basualdo J, Pezzani B, De Luca M, Córdoba A, Apezteguía M (2000). "Screening of the municipal water system of La Plata, Argentina, for human intestinal parasites". Int J Hyg Environ Health 203 (2): 177–82. doi:10.1078/S1438-4639(04)70025-5. PMID 11109572.
- Puthia MK, Sio SW, Lu J, Tan KS (2006). "Blastocystis ratti Induces Contact-Independent Apoptosis, F-Actin Rearrangement, and Barrier Function Disruption in IEC-6 Cells". Infect. Immun. 74 (7): 4114–23. doi:10.1128/IAI.00328-06. PMC 1489721. PMID 16790785.
- al-Tawil YS, Gilger MA, Gopalakrishna GS, Langston C, Bommer KE (1994). "Invasive Blastocystis hominis infection in a child". Archives of pediatrics & adolescent medicine 148 (8): 882–5. doi:10.1001/archpedi.1994.02170080112026. PMID 8044274.
- Long HY, Handschack A, König W, Ambrosch A (2001). "Blastocystis hominis modulates immune responses and cytokine release in colonic epithelial cells". Parasitol. Res. 87 (12): 1029–30. PMID 11763434.
- Puthia MK, Vaithilingam A, Lu J, Tan KS (2005). "Degradation of human secretory immunoglobulin A by Blastocystis". Parasitol. Res. 97 (5): 386–9. doi:10.1007/s00436-005-1461-0. PMID 16151742.
- McGowan K, Kane A, Asarkof N et al. (1983). "Entamoeba histolytica causes intestinal secretion: role of serotonin". Science 221 (4612): 762–4. doi:10.1126/science.6308760. PMID 6308760.
- McGowan K, Guerina V, Wicks J, Donowitz M (1985). "Secretory hormones of Entamoeba histolytica". Ciba Found. Symp. 112: 139–54. doi:10.1002/9780470720936.ch8. PMID 2861068.
- Banu, Naheed et al. (2005). "Neurohumoral alterations and their role in amoebiasis" (PDF). Indian J. Clin Biochem 20 (2): 142–5. doi:10.1007/BF02867414. PMC 3453840. PMID 23105547.
- Boorom KF, Smith H, Nimri L et al. (2008). "Oh my aching gut: irritable bowel syndrome, Blastocystis, and asymptomatic infection". Parasit Vectors 1 (1): 40. doi:10.1186/1756-3305-1-40. PMC 2627840. PMID 18937874.
- Stensvold CR, Smith HV, Nagel R, Olsen KE, Traub RJ (October 2009). "Eradication of Blastocystis Carriage With Antimicrobials: Reality or Delusion?". J. Clin. Gastroenterol. 44 (2): 85–90. doi:10.1097/MCG.0b013e3181bb86ba. PMID 19834337.
- Haresh K, Suresh K, Khairul Anus A, Saminathan S (1999). "Isolate resistance of Blastocystis hominis to metronidazole". Trop. Med. Int. Health 4 (4): 274–7. doi:10.1046/j.1365-3156.1999.00398.x. PMID 10357863.
- Moghaddam DD, Ghadirian E, Azami M (2005). "Blastocystis hominis and the evaluation of efficacy of metronidazole and trimethoprim/sulfamethoxazole". Parasitol. Res. 96 (4): 273–5. doi:10.1007/s00436-005-1363-1. PMID 15915364.
- Rossignol JF, Kabil SM, Said M, Samir H, Younis AM (2005). "Effect of nitazoxanide in persistent diarrhea and enteritis associated with Blastocystis hominis". Clin. Gastroenterol. Hepatol. 3 (10): 987–91. doi:10.1016/S1542-3565(05)00427-1. PMID 16234044.
- Armentia A, Méndez J, Gómez A et al. (1993). "Urticaria by Blastocystis hominis. Successful treatment with paromomycin". Allergologia et immunopathologia 21 (4): 149–51. PMID 8237719.
- Grossman I, Weiss LM, Simon D, Tanowitz HB, Wittner M (1992). "Blastocystis hominis in hospital employees". Am. J. Gastroenterol. 87 (6): 729–32. PMID 1590309.
- Dunn LA, Boreham PF (1991). "The in-vitro activity of drugs against Blastocystis hominis". J. Antimicrob. Chemother. 27 (4): 507–16. doi:10.1093/jac/27.4.507. PMID 1856129.
- Gonçalves AQ, Viana Jda C, Pires EM, Bóia MN, Coura JR, Silva EF (2007). "The use of the antifungal agent miconazole as an inhibitor of Blastocystis hominis growth in Entamoeba histolytica/E. dispar cultures". Rev. Inst. Med. Trop. Sao Paulo 49 (3): 201–2. doi:10.1590/S0036-46652007000300013. PMID 17625701.
- Zierdt CH, Swan JC, Hosseini J (1983). "In vitro response of Blastocystis hominis to antiprotozoal drugs". J. Protozool. 30 (2): 332–4. doi:10.1111/j.1550-7408.1983.tb02925.x. PMID 6631776.
- White AC (2000). "The disappearing arsenal of antiparasitic drugs". N. Engl. J. Med. 343 (17): 1273–4. doi:10.1056/NEJM200010263431718. PMID 11183360.
- van Hal SJ, Stark DJ, Fotedar R, Marriott D, Ellis JT, Harkness JL (2007). "Amoebiasis: current status in Australia". Med. J. Aust. 186 (8): 412–6. PMID 17437396.
- Amin OM (2002). "Seasonal prevalence of intestinal parasites in the United States during 2000". Am. J. Trop. Med. Hyg. 66 (6): 799–803. PMID 12224595.
- Lagacé-Wiens PR, VanCaeseele PG, Koschik C (2006). "Dientamoeba fragilis: an emerging role in intestinal disease". Canadian Medical Association Journal 175 (5): 468–9. doi:10.1503/cmaj.060265. PMC 1550747. PMID 16940260.
- Yakoob J, Jafri W, Jafri N et al. (2004). "Irritable bowel syndrome: in search of an etiology: role of Blastocystis hominis". Am. J. Trop. Med. Hyg. 70 (4): 383–5. PMID 15100450.
- McClure, H. M., E. A. Strobert (1980). "Blastocystis hominis in a pig-tailed macaque: a potential enteric pathogen for non-human primates". Lab. Anim. Sci. 30 (5): 890–899. PMID 7191935.