Blastocystis hominis

Blastocystis hominis
Clinical Aspects
Treatment and Control

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B. hominis is an intestinal protozoa which is an unicellular anaerobic organism that inhabits the human intestinal tract.

There is no a single issue about this organism that has been satisfactorily resolved. Structures and organelles present in the cell remain of unknown function. The method(s) of division is questioned. The pathogenicity of the organism is still unknown.

The infection may be symptomatic or asymptomatic, but most of the patients are asymptomatic. The symptoms are diarrhea, stomachache, nausea, vomiting, flatulence or fatigue. The factor determining the different outcomes is still inconclusive.

It may be found in stool specimens from both normal hosts and immunocompromized hosts.

The necessity for treatment and the most appropriate chemotherapeutic agents have not been defined.



The first paper to clearly define the genus Blastocystis was presented by Alexeieff, who proposed the name B. enterocola. An extensive morphological description was given, and a life cycle was presented. Brumpt proposed the name B. hominis for the organism isolated from human fecal material, and this is the name recognized in the current literature.

Very few data were published until the work of Zierdt et al. renewed interest in the organism.

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To date the taxonomy of Blastocystis is still controversial. A molecular phylogenetic analysis based on the comparison of small-subunit (SSU) rRNA gene sequences demonstrated that Blastocystis is placed within the stramenopiles, a diverse group of mostly unicellular eukaryotes which includes brown algae, chrysophytes, oomycetes, and diatoms. A recent combined analysis of eight molecules demonstrated that B. hominis is positioned within stramenopiles, corroborating previous SSU rRNA-based trees and indicating that Blastocystis/stramenopiles are the closest relatives of alveolates (apicomplexans, ciliates, and dinoflagellates).

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Summarized by Thirayost Nimmanon



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