Blastocystis | |
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Blastocystis sp. | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Clade: | Diaphoretickes |
Clade: | SAR |
Clade: | Stramenopiles |
Phylum: | Bigyra |
Subphylum: | Opalozoa |
Infraphylum: | Placidozoa |
Superclass: | Opalinata |
Class: | Blastocystea Zierdt et al. 1967 |
Order: | Blastocystida Zierdt 1978 |
Family: | Blastocystidae Jiang & He 1988 |
Genus: | Blastocystis (Alexieff 1911) Brumpt 1912[1] |
Blastocystis is a genus of single-celled parasites belonging to the Stramenopiles that includes algae, diatoms, and water molds. There are several species, living in the gastrointestinal tracts of species as diverse as humans, farm animals, birds, rodents, reptiles, amphibians, fish, and cockroaches.[2] Blastocystis has low host specificity, and many different species of Blastocystis can infect humans,[3] and by current convention, any of these species would be identified as Blastocystis hominis.
Blastocystis is one of the most common human parasites in the world and has a global distribution.[4][5][6][7] It is the most common parasitic infection in the United States, where it infected approximately 23% of the total population during year 2000.[6][7] In less developed areas, infection rates as high as 100% have been observed.[4][5] High rates of infection are found in individuals in developed countries who work with animals.[5][8] Although the role of Blastocystis hominis in human disease is often referred to as controversial, a systematic survey of research studies conducted by 11 infectious disease specialists from nine countries, found that over 95% of papers published in the 10 years prior identified it as causing illness in immunocompetent individuals.[7] The paper attributed confusion over pathogenicity to the existence of asymptomatic carriers, a phenomenon the study noted is common to all gastrointestinal protozoa.[7] However, Blastocystis has never fulfilled Koch's postulate that infection of a healthy individual with Blastocystis leads to disease. The fact that Blastocystis' infection route is oral-anal indicates that carriers have been in contact with faecal contaminated matter which might have included other intestinal pathogens that explain the observed symptoms. A more likely explanation is the presence of virulent and non-virulent strains since there exists an enormous genetic variation between different strains (or genotypes). See the genotype paper by Rune Stensvold[9] and the 2017 Blastocystis genome paper[10] expanding on this diversity. An alternative theory that Blastocystis is not a pathogen at all has recently been strengthened based on its biochemistry.[11][12]
Blastocystis is one of the most common intestinal protists of humans. ... A recent study showed that 100% of people from low socio-economic villages in Senegal were infected with Blastocystis sp. suggesting that transmission was increased due to poor hygiene sanitation, close contact with domestic animals and livestock, and water supply directly from well and river [10]. ...
Parasitologic investigations of large patient populations are rarely conducted in the United States, where the illusion of freedom from parasitic infections still predominates. Such investigations are considerably more common in third-world countries where endemic parasitoses are more readily documented.1 In an attempt to address this problem we reported the results of routine examination of fecal specimens for parasites from 644 patients in the United States during the summer of 1996. ...
Prevalence. Nine hundred sixteen (32%) of 2,896 tested patients were infected with 18 species of intestinal parasites in the year 2000 (Table 1) in 48 states and the District of Columbia as follows ... Blastocystis hominis was the most frequently detected parasite in single and multiple infections, with Cryptosporidium parvum and Entamoeba histolytica/E. dispar ranking second and third, respectively.
Blastocystis is now by far the most prevalent mono-infection in symptomatic patients in the United States [14] and was found 28.5 times more often than Giardia lamblia as a mono-infection in symptomatic patients in a 2000 study [14].