Trypanosoma
Trypanosomes ( Trypanosoma, Greek drill body, the form of a drill -like cell bodies ) are a genus of unicellular flagellated flagellates which live as parasites in various vertebrates, from fish to mammals and are usually transmitted by insects. Most species are harmless. However, infections with trypanosomes in humans in Africa and Latin America are a major medical problem: subspecies of Trypanosoma brucei, the causative agent of African sleeping sickness disease and Trypanosoma cruzi is the causative agent of Chagas disease. In addition, trypanosome infections in different livestock in tropical and subtropical countries have great economic importance; important animal diseases caused by trypanosomes are the nagana and surra.
Discovery and description
The first representative of the genus in 1843 by the Hungarian doctor David Gruby ( 1810-1898 ) describes the Trypanosoma sanguinis observed in the blood of a frog. The genus name Trypanosoma is composed of the Greek word tryp - ( pierce, perforate ) together and the noun soma (body) and refers to a drill or corkscrew -like, elongated spiral shape of the cells and their mode of locomotion. After the trypanosomes were several decades regarded as a harmless parasite, succeeded in 1880 to the British Veterinary Griffith Evans ( 1835-1935 ) to identify trypanosomes as the cause of Surra, soon followed by the discovery of the causative agent of nagana by David Bruce. The human pathogenic parasites were first described in the early 20th century.
The most slender cells can be up to 80 microns long depending on the type, the fish -infecting parasites are particularly large. The important pathogens among the trypanosomes, the cells are more than 30 to 40 microns long. The single-celled organisms have a characteristic of the Kinetoplastea kinetoplast, a pronounced accumulation of deoxyribonucleic acid in a mitochondrion. Trypanosomes have a single flagellum without mastigonema. The whip is located on the cell surface and forms with this an undulating membrane. Many trypanosomes change during the lifecycle of its shape, it varies especially the position of the flagellum relative to the cell nucleus and the length of the cell itself
One can therefore distinguish several forms:
- Trypomastigote forms in which the scourge on cell rear end outlet downstream of the core
- Epimastigotes forms in which the whip exits in the cell center of the core
- Amastigote forms in which no free flagellum is visible.
Promastigote forms in which the scourge exit at the front end of the cell, do not occur in the GattungTrypanosoma.
Distribution and host animals
Trypanosomes are found worldwide. Each species has a limited range of intermediate hosts, therefore they can exist only in areas where this intermediate host occurs. One example is the " tsetse belt" in Africa in Trypanosoma brucei; this parasite is only found in the circulation area of the tsetse fly. In humans, disease -causing trypanosomes are found almost exclusively in sub-Saharan Africa and Latin America.
There are trypanosomes, the terrestrial mammals, reptiles or birds infect, but also infect parasites that amphibians or live in fresh water or sea fish. The parasites of terrestrial animals are insects responsible for the transmission usually: Important intermediary for the pathogens in humans and animals are predatory bugs, tsetse flies and brakes; various rodents infesting trypanosomes are thought to be transmitted by fleas while in birds black flies and louse flies are the vectors. In fish and amphibians, leeches take on this role.
Life cycle
All trypanosomes live parasitically and make a host of changes between one invertebrate vector and a vertebrate host by. In the invertebrate vector often is, but not in all cases to increase their number; some species such as Trypanosoma evansi is transmitted by insects mechanically without multiplication, Trypanosoma equiperdum without insect host during mating from horse to horse. As a rule, in the intestinal tract of insects evolving forms are epimastigot while trained in the vertebrate host trypomastigote forms. In vertebrates, the parasites live in body fluids such as blood, lymph or cerebrospinal fluid. Some species, such as Trypanosoma cruzi, multiply as amastigote form inside host cells to escape the activity of the immune system of the vertebrate host. Other trypanosome Trypanosoma brucei as have developed elaborate mechanisms of antigenic variability in the variable surface glycoproteins of the cell membrane to be replaced frequently, to avoid an acquired immunity of the host.
Molecular properties
Trypanosomes were studied because of their medical importance, for decades. Here some peculiarities were discovered especially in gene expression that are unusual for eukaryotes. How many genes are transcribed as polycistronic transcript. The control of gene expression is primarily post-transcriptionally via mRNA stabilization and degradation. The polycistronic transcript is trans- spliced into a monocistronic mRNA which can be translated to the corresponding proteins. The trans-splicing was first observed in trypanosomes. Meanwhile, the complete sequence of the genome were determined for several trypanosome.
System
Outer systematics
The trypanosomes are currently one of eleven genera within the trypanosomatid. In the trypanosomatid genus Leishmania has the next Trypanosoma also great medical importance. Sometimes colloquially insect " trypanosomes " species mentioned do not belong to the genus Trypanosoma but are classified in the genera Blastocrithidia, Crithidia, Herpetomonas, Leptomonas or Rhynchoidomonas; parasitic in plants " trypanosomes " belong to the genus Phytomonas.
It is likely that the genus Trypanosoma is monophyletic; However, this is not without controversy because of differing results from sequence comparisons of ribosomal nucleic acids and different protein families.
Inside systematics
Several hundred species have been described in the genus Trypanosoma. The genus has been divided into two large groups without taxonomic rank: the Sterocoraria that proliferate in the hindgut of the insect and are spread by infectious feces, and the Salivaria that are transmitted by a bite from the insect during blood feeding. These groups were further divided into seven subgenera because of their shape and their life cycle.
Among the currently recognized species have the following medical or veterinary importance:
- Genus Trypanosoma Sterocoraria Subgenus Megatrypanum Hoare, 1964 Type Trypanosoma theileri Laveran, 1902
- Trypanosoma lewisi type Laveran and Mesnil, 1901
- Type Trypanosoma cruzi Chagas 1909; Agent of Chagas' disease in man.
- Trypanosoma rangeli Tejera type, 1920
- Subgenus Duttonella Chalmers, 1918 Trypanosoma vivax Ziemann Art, 1905; Causative agent of nagana in various ruminants.
- Type Trypanosoma congolense Broden, 1904; Causative agent of nagana.
- Trypanosoma simiae type Bruce et al., 1912
- Type Trypanosoma godfreyi McNamara et al., 1944
- Type Trypanosoma brucei Plimmer and Bradford, 1899; Subspecies are causing sleeping sickness in humans and nagana.
- Type Trypanosoma evansi Balbiani, 1888; Causative agent of surra in horses and camels.
- Trypanosoma equiperdum kind Doflein, 1901; Causative agent of dourine in horses.
- Trypanosoma suis type Ochmann, 1905
Sequence analysis confirmed the distinction between the predominantly American trypanosomes of the subgenus Schizotrypanum and the predominantly African trypanosomes of Salivaria group but identified beyond other clades, including a rodent -infecting clade, a birds infecting clade and an aquatic clade that affects fish and amphibians. The currently valid taxonomy not yet considered these results; several subgenera are considered to be paraphyletic.