Plasmodia
| Plasmodia | ||||||||||||
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Plasmodium malariae |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Plasmodiidae | ||||||||||||
| Mesnil , 1903 | ||||||||||||
| Genera | ||||||||||||
Plasmodia (Plasmodiidae) are unicellular parasites that mainly infect mammals ( Mammalia ) and two-winged birds ( Diptera ). They are divided into the tribe of the Apicomplexa . In the Plasmodium family there are four subfamilies with up to 170 species, see also Plasmodium . The plasmodia belong to the sporozoa .
features
Plasmodia are unicellular organisms that do not have a cell wall, but as eukaryotes, in contrast to bacteria and archea (prokaryotes), have a cell nucleus . They are comma-shaped and quite slender, due to their way of life they take on different shapes depending on the host and stage of development. The smallest form, trophozoite , measures three microns , the largest form of liver schizont up to 70 microns.
In heterozygous carriers of sickle cell anemia , a plasmodia infection is much weaker than in healthy individuals. In areas where malaria (a disease caused by Plasmodia) is widespread, carriers of this hereditary disease have a ( selective ) advantage. Therefore, the percentage of heterozygous carriers in the population in such areas is significantly higher than in malaria-free regions.
distribution
Plasmodia are found today mainly in tropical and subtropical regions; as their development depends strongly on the temperature, even there plasmodia only occur up to an altitude of less than 1500 meters. They were also widespread in northern Europe up to the 19th century, but were eradicated by river straightening and swamp drainage. Remnants can still be found in Central Asia: Armenia , Georgia , Kazakhstan , Kyrgyzstan , Tajikistan , Turkey , Turkmenistan and Uzbekistan .
Life cycle
Mosquitoes , especially of the genus Anopheles , serve as final hosts ; Plasmodia multiply in them, and humans serve as intermediate hosts . There are four types of plasmodia that cause malaria in humans; they belong to the genus Plasmodium . After being bitten by an infected anopheles mosquito, it secretes sporozoites with its saliva, which contains anticoagulants . These are carried with the bloodstream to the liver, where they penetrate the cells of the liver tissue and mature into liver schizont. This is where their reproduction takes place, which is called "exoerythrocytic schizogony"; this creates up to 30,000 merozoites . Plasmodium vivax and Plasmodium ovale insert rest phases between these stages; thereby remain Hypnozoiten undivided in the liver tissue and thus provide per month for a new infection, even if the initial infection was overcome. The merozoites enter the bloodstream and then infect red blood cells . They penetrate this and begin to divide intracellularly . Eight to sixteen new merozoites result from this division . The following division times have been observed in the four plasmodia infesting humans:
| Plasmodium | Malaria form | Division duration |
|---|---|---|
| P. ovale | Malaria tertiana | 48 hours |
| P. vivax | Malaria tertiana | 48 hours |
| P. malariae | Quartana malaria | 72 hours |
| P. falciparum | Malaria tropica | irregular |
After division, residues of the hemoglobin absorbed by the merozoite are released , the hemozoin , which triggers the fever attacks typical of malaria . After the production of merozoites, which lasts a few days to weeks , some start to mature into sexually mature cells ( gametocytes ). These are now found in the blood together with the merozoites (see also: Generational change ).
Fever attacks and the accompanying sweating make infected carriers attractive again for mosquitoes, as they have a good sense of smell and temperature. If the mosquito bites again, these gametocytes are ingested, where they combine to form a wandering zygote . This then gives rise to the ookinet , which is deposited between the tissue layers of the mosquito stomach and becomes an oocyst there; up to 1,000 new sporozoites develop in it . From there they migrate into the mosquito's salivary glands and are ready to re-infect an intermediate host , for example humans.
