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 the development of irritable bowel syndrome.
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, 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 (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: 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 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 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'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. 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. 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 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.
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.