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Trypanosoma cruzi parasites
Scientific classification
Domain: Eukaryota
(unranked) Excavata
Phylum: Euglenozoa
Subphylum: Mastigophora
Class: Kinetoplastea
Order: Trypanosomatida


Trypanosomes are a group of kinetoplastid protozoa distinguished by having only a single flagellum. All members are exclusively parasitic, found primarily in insects. A few genera have life-cycles involving a secondary host, which may be a vertebrate or a plant. These include several species that cause major diseases in humans.

The most notable trypanosomal diseases are trypanosomiasis (African Sleeping Sickness and South American Chagas Disease); these are caused by species of Trypanosoma. Leishmaniasis is a trypanosomal disease caused by species of Leishmania.

A variety of different forms appear in the life-cycles of trypanosomes, distinguished mainly by the position of the flagellum:

Amastigote (leishmanial) - reduced or absent
Promastigote (leptomonad) - anterior of nucleus, free from cell body
Epimastigote (crithidial) - anterior of nucleus, connected by a short undulating membrane
Opisthomastigote (herpetomonad) - posterior of nucleus, passing through a long groove in the cell
Trypomastigote (trypanosomal) - posterior of nucleus, connected by a long undulating membrane

All trypanosomes have at least amastigote and promastigote stages. Trypanosoma appears in all five forms, with the trypanosomal stage occurring in the vertebrate host. Trypanosoma brucei sub-species have two forms in the bloodstream of a vertebrate host, the rapidly dividing long-slender form and the non-dividing short stumpy form. The short stumpy parasites are adapted for uptake into the tsetse fly vector, and are non-proliferative in comparison with the slender forms.

Unique to Trypansoma brucei is the expression of a variable surface glycoprotein (VSG) coat on the cell surface, which undergoes constant variation in order to evade the humoral immune system and host antibodies. It is thought that recombination from a repertoire of >1000 VSG genes is responsible for the vast diversity of the parasite, and its effectiveness in immune evasion.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Trypanosome". A list of authors is available in Wikipedia.
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