Plasmodium malariae
| Plasmodium malariae | ||||||||||||
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Mature schizont of Plasmodium malariae in stained blood smear |
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| Scientific name | ||||||||||||
| Plasmodium malariae | ||||||||||||
| ( Grassi & Feletti , 1890) |
Plasmodium malariae is a protozoan parasite of the genus of the plasmodia and the pathogen of Malaria quartana in humans, a relatively benign form of the disease is rarely fatal. Like other malaria pathogens , Plasmodium malariae is transmittedby Anopheles mosquitoes . Today the parasite is mainly found in tropical countries.
Discovery and Description
history
Malaria pathogens were first described by Alphonse Laveran in 1880 . Angelo Celli examined the parasite together with Ettore Marchiafava and named it Plasmodium malariae in 1885 . Laveran assumed only one type of pathogen, which he called Oscillaria malariae ; It is believed that Laveran observed pathogens causing tropica malaria, tertiana malaria and quartana malaria in Algiers. It was only in 1886 that Camillo Golgi was able to differentiate between these different disease courses and their pathogens . In 1890, after reviewing the literature, Grassi and Feletti proposed the name Haemamoeba malariae for the causative agent of Quartana malaria ; a number of other name suggestions from other authors followed. In 1885 Marchiafava and Celli had already proposed the generic name Plasmodium . In 1954, the common combination Plasmodium malariae was declared valid by the International Commission on Zoological Nomenclature .
morphology
As with all plasmodia, P. malariae occurs in various stages of development. Mosquito sporozoites are comparatively large with a diameter of 12 micrometers. Liver schizonts reach a diameter of around 50 micrometers and contain many thousands of merozoites . When the parasite multiplies in erythrocytes , these are usually not enlarged. Mature blood schizonts contain 6 to 14, typically 8, merozoites. Immature gametocytes cannot be distinguished microscopically from the asexual forms. The mature gametocytes fill the host cell completely. After staining, macrogametocytes show a deep blue cytoplasm with a small nucleus at the edge and dispersed pigment, while the microgametocytes show a light blue cytoplasm with a diffuse nucleus.
Differentiating between different malaria pathogens simply through the morphology in the blood smear can be difficult or even impossible. In Southeast Asia, infections with Plasmodium knowlesi were wrongly identified as those with P. malariae . To avoid such errors, molecular DNA techniques are increasingly used for differentiation.
Systematics
Traditionally, Plasmodium malariae is classified in the subgenus Plasmodium with many other plasmodia that infect primates . Very closely related or identical to P. malariae is P. brasilianum , a parasite described in various New World monkeys in Central and South America, which cannot be distinguished from P. malariae microscopically and molecularly . It is believed that P. malariae reached South America through infected humans in the past 500 years and was also transmitted from these to monkeys by mosquitoes. In West Africa, another parasite, P. rodhaini, has been described in chimpanzees and gorillas , which cannot be distinguished from P. malariae . Generally P. rodhaini is regarded as a synonym of P. malariae . Apart from these two plasmodia, no other species are particularly closely related to P. malariae . The evolutionary origin of P. malariae is unclear.
Distribution and host animals
Plasmodium malariae occurs in tropical and subtropical areas and is widespread in sub-Saharan Africa, but can also be found in Southeast Asia and on islands in the western Pacific and the Amazon basin. P. malariae was also originally found in Europe and the southern United States.
In general, humans are regarded as the only reservoir host for Plasmodium malariae . It is unclear whether infected monkeys represent an epidemiologically relevant reservoir for human infections. The parasites identified in monkeys are believed to be anthropozoonoses . To research the disease, owl monkeys can be infected experimentally , among other things .
A whole range of Anopheles species can be used as vectors for P. malariae , including species that occur in Europe such as Anopheles atroparvus or Anopheles messeae .
Life cycle
The life cycle of P. malariae is essentially the same as that of other plasmodia. The parasite shows an obligatory change of host. The sporozoites get into the bloodstream of humans through infected mosquitoes, migrate from there to the liver and penetrate into hepatocytes , in which they reproduce asexually. Compared to other malaria pathogens, the incubation time of this liver phase is at least 15 days, which is comparatively long. The liver schizonts each produce thousands of merozoites, which are released and attack red blood cells, where further asexual reproduction takes place. The generation time for reproduction in the erythrocytes is about 72 hours. Since development is synchronous, there is a massive release of new parasites at the end of each reproduction cycle, which is associated with a fever. The term malaria quartana is derived from the periodicity of the fever attacks. A few plasmodia develop into sex forms in the erythrocytes. These microgametocytes and macrogametocytes can be ingested by mosquitoes with a blood meal and start a new development cycle in the insect's intestine. After the gametes fuse, new sporozoites are formed in the intestine that migrate to the salivary gland, from where they can be transferred to a new host. The development time in the mosquito is 15 to 21 days.
A peculiarity in the life cycle of P. malariae is the occurrence of recrudescences, which are relapses that arise from persistent erythrocyte forms. In individual cases, these appear even after decades if the parasites have not been eliminated by a suitable therapy. In contrast, P. malariae does not have recurrences resulting from hypnozoites in the liver .
literature
- G. Robert Coatney, William E. Collins, McWilson Warren, and Peter G. Contacos: The primate malarias. Bethesda: US National Institute of Allergy and Infectious Diseases, 1971. Chapter 18, pp. 209 ff .: Plasmodium malariae
- William E. Collins and Geoffrey M. Jeffery: Plasmodium malariae: Parasite and Disease. In: Clin. Microbiol. Rev. 2007, Vol. 20 (4), pp. 579-592 PMID 17934075
Individual evidence
- ↑ Manfred Vasold: Celli, Angelo. In: Werner E. Gerabek , Bernhard D. Haage, Gundolf Keil , Wolfgang Wegner (eds.): Enzyklopädie Medizingeschichte. De Gruyter, Berlin / New York 2005, ISBN 3-11-015714-4 , p. 234.