Blastocystis

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Blastocystis
Blastocystis sp.

Blastocystis sp.

Systematics
Classification : Creature
Domain : Eukaryotes (eukaryota)
without rank: Diaphoreticks
without rank: Sar
without rank: Stramenopiles (stramenopiles)
Genre : Blastocystis
Scientific name
Blastocystis
(Alexieff 1911) Rumps 1912

Blastocystis is a genus of unicellular , facultatively pathogenic parasites from the stramenopil group . They live strictly anaerobic , are not very host-specific and occur in the digestive tract of different animal species . Hosts can e.g. B. humans , farm animals , rodents , birds , reptiles , amphibians or cockroaches . The infection rate in humans fluctuates widely and ismostly below 10%in industrialized countries , but canalso exceed 50%in tropical developing countries .

Systematics

Originally, due to its yeast-like appearance and no locomotive organs, it was assumed that Blastocystis was a yeast or another fungus . Later it was added to the Sporozoa . It was not until 1996 that it was possible to demonstrate that it belonged to the stramenopile on the basis of the rRNA sequence.

Within the genus Blastocystis , a separate species was originally described for each infected species. So was z. B. Blastocystis hominis described and in the rat Blastocystis ratti . In recent years, however, genetic testing has shown that different strains of Blastocystis can be assigned to different species in humans. It was also shown that individual Blastocystis strains can infect a large number of hosts. Therefore, the move was made to subdivide Blastocystis only into subtypes that are differentiated on the basis of their DNA sequence . The proposed name is therefore Blastocystis sp. Subtype nn, where nn denotes the number of the respective subtype. At least 13 of these subtypes are currently known, most of which can also affect humans. It is very likely that further subtypes will be discovered as more animal species are analyzed .

infection

Infection rates with Blastocystis are higher in tropical countries than in cooler regions . In addition, industrialized countries with an infection rate of 1–10% are significantly less affected than developing countries with an infection rate of up to 76%.

Various studies show that between 50 and 80% of all people infected with blastocystis show symptoms . Symptoms commonly associated with blastocystis include irritable bowel syndrome , diarrhea , constipation , flatulence , nausea , abdominal cramps, gas , weight loss, and fatigue . More rarely, skin rashes , headaches , depression , joint pain and inflammation of the intestines . Originally it was thought that some subtypes of Blastocystis cause symptoms while other subtypes do not cause symptoms. Malaysian scientists reported that large amounts of amoeboid cells were found in symptomatic patients , while these could not be detected in asymptomatic patients. In subsequent studies , however, scientists found that subtypes from symptomatic patients could not trigger symptoms in other patients and concluded that host factors such as age or genetics have a greater influence on symptoms than the subtype of blastocystis .

The transmission occurs faecal-orally via contaminated drinking water or contaminated food . Presumably only the cystic form is transmitted. Genomic studies confirm the transmission from person to person, from person to animal and from animal to person, although the proportion of the respective transmission path is still unknown. If animal-to-human transmission occurs, farm animals such as pigs or dogs could represent a reservoir of pathogens . This is also indicated by the fact that people who work in agriculture and who have frequent contact with the animals in question are more likely to be infected with blastocystis .

The diagnosis of blastocystis is usually made microscopically today , although this test is relatively unreliable. But antibody tests are now also possible. In the event of an infection, oral treatment with metronidazole , which, however, has also been reported to be resistant , or (the only questionable availability in Germany) quinoline derivative iodoquinol is possible if a connection between the symptoms and blastocystis is assumed. However, studies have shown that 40% of all strains are resistant to this drug .

morphology

Blastocystis can take several forms , depending on environmental conditions , the most common of which is the vacuolar form. There are also multivacuolar, avacuolar, granular, cystic and amoeboid forms.

Vacuolar form

Typical and most frequently found shape, which can vary in size between 2 and 200 µm. A large central vacuole fills almost the entire volume and is only surrounded by a thin layer of cytoplasm in which the other organelles are located. A fluffy substance is unevenly distributed in the vacuole. It is assumed that the central vacuole serves as a storage organ, but other tasks such as cell division are also possible. There are 1–4 nuclei in each cell .

Granular shape

Has a similar structure to the vacuolar form, but there are also granules both in the cytoplasm and in the vacuole. Different types of granules are thought to have a role in metabolism and reproduction . The cells vary in size between 6.5 and 80 µm and also have 1–4 nuclei.

Cystic form

3–10 µm in size and surrounded by a thick cell wall. Also has 1–4 nuclei per cell and several small vacuoles. Due to the thick cell wall, this is the most resilient form, which enables survival even under difficult conditions, such as in gastric acid , in distilled water or for a long time at room temperature . This form is the form of spread that is spread from organism to organism.

Amoeboid form

This shape is between 2.6 and 7.8 µm in size and has 1–2 cell nuclei. It is stationary and strongly adhesive . Since it could only be detected in infected people with symptoms, it is assumed that it is responsible for the symptoms by attaching to the intestinal wall .

Life cycle

The life cycle of Blastocystis is still relatively unexplored, so this only describes the presumed life cycle. The unit of distribution is the cystic form excreted by infected individuals and ingested through contaminated water or food. The cysts infect the epithelial cells of the digestive tract, where they transform into vacuolar cells and asexually reproduce. Vacuolar cells can then either multivakuoläre cells convert extending through schizogony asexually multiply, or in amoeboid cells. The amoeboid cells can also reproduce asexually through mitosis and transform into pre-cysts, which transform into thick-walled cysts through schizogony. If these thick-walled cysts are excreted and absorbed by another organism, the life cycle begins again.

Blastocystis life cycle , suggested by Tan

Mitochondrion-like organelles

Although Blastocystis lives strictly anaerobically, it has organelles that are derived from mitochondria . The genome of these organelles codes for some subunits of NADH dehydrogenase , but not for cytochrome or ATPase , so that only an incomplete respiratory chain exists. It is therefore suggested that an alternative oxidase is present. There are also other similarities with mitochondria in terms of metabolism . Furthermore, genome investigations show a [FeFe] hydrogenase which is localized in the organelles as a common feature with hydrogenosomes .

Web links

Commons : Blastocystis  - collection of images, videos and audio files

Individual evidence

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