Трипаносоматидтер: құрылысы, тіршілік циклі және аурулары

Flagellate kinetoplastid excavate order

Trypanosomatida is a group of kinetoplastid unicellular organisms distinguished by having only a single flagellum. The name is derived from the Greek trypano (borer) and soma (body) because of the corkscrew like motion of some trypanosomatid species. All members are exclusively parasitic, found primarily in insects. A few genera have life cycles involving a secondary host, which may be a vertebrate, invertebrate or plant. These include several species that cause major diseases in humans. Some trypanosomatida are intracellular parasites, with the important exception of Trypanosoma brucei.

The three major human diseases caused by trypanosomatids are; African trypanosomiasis (sleeping sickness, caused by Trypanosoma brucei and transmitted by tsetse flies), South American trypanosomiasis (Chagas disease, caused by T. cruzi and transmitted by triatomine bugs), and leishmaniasis (a set of trypanosomal diseases caused by various species of Leishmania transmitted by sandflies).

The family is known from fossils of the extinct genus Paleoleishmania preserved in Burmese amber dating to the Albian (100 mya) and Dominican amber from the Burdigalian (20–15 mya) of Hispaniola. The genus Trypanosoma is also represented in Dominican amber in the extinct species T. antiquus.

Some trypanosomatids only occupy a single host, while many others are heteroxenous: they live in more than one host species over their life cycle. This heteroxenous life cycle typically includes the intestine of a bloodsucking insect and the blood and/or tissues of a vertebrate. Rarer hosts include other bloodsucking invertebrates, such as leeches, and other organisms such as plants. Different species go through a range of different morphologies at different stages of the life cycle, with most having at least two different morphologies. Typically the promastigote and epimastigote forms are found in insect hosts, trypomastigote forms in the mammalian bloodstream and amastigotes in intracellular environments. Among commonly studied examples, T. brucei, T. congolense, and T. vivax are extracellular, while T. cruzi and Leishmania spp. are intracellular.

Trypanosomatids that cause globally known diseases such leishmaniasis (Leishmania species), African trypanosomiasis referred to as sleeping sickness (Trypanosoma brucei), and Chagas disease (Trypanosoma cruzi) were found to be capable of meiosis and genetic exchange. These findings indicate the capability for sexual reproduction in the Trypanosomatida. Amastigotes are a common morphology during an intracellular lifecycle stage in a mammalian host. All Leishmania have an amastigote stage of the lifecycle. Leishmania amastigotes are particularly small and are among the smallest eukaryotic cells. The flagellum is very short, projecting only slightly beyond the flagellar pocket. (leptomonad). A morphotype where the flagellum does not extend beyond the deep flagellar pocket.

Notable characteristics of trypanosomatids are the ability to perform trans splicing of RNA and possession of glycosomes, where much of their glycolysis is confined to. The acidocalcisome, another organelle, was first identified in trypanosomes.

Six species of trypanosomatids are known to carry an additional proteobacterial endosymbiont, termed TPE (trypanosomatid proteobacterial endosymbionts). These trypansomatids (Strigomonas oncopelti, S. culicis, S. galati, Angomonas desouzai, and A. deanei) are in turn known as SHTs, for symbiont harboring trypanosomatids. All such symbionts have a shared evolutionary origin and are classified in the Candidatus genus "Kinetoplastibacterium". As with many symbionts, the bacteria have a much reduced genome compared to their free living relatives of genera Taylorella and Achromobacter. (GTDB finds the genus sister to Proftella, a symbiont of Diaphorina citri.) Reflecting their inability to live alone, they have lost genes dedicated to essential biological functions, relying on the host instead. They have modified their division to become synchronized with the host. In S. culicis at least, the TPE helps the host by synthesizing heme