Trypanosomatida

Trypanosomatida is an order of flagellated protists within the class Kinetoplastea. They are predominantly parasitic, infecting vertebrates, invertebrates, and plants. A defining feature is the kinetoplast, a network of circular DNA within a single mitochondrion, which is visible in many forms. Members possess a single anterior flagellum that emerges from a flagellar pocket and is supported by a subpellicular cytoskeleton.

Most species display heteroxenous life cycles, alternating between an insect vector and a vertebrate or plant host. In humans and other mammals, major pathogens include Trypanosoma brucei (causing human African trypanosomiasis), T. cruzi (Chagas disease), and Leishmania spp. (leishmaniasis). Transmission vectors include tsetse flies (T. brucei), triatomine bugs (T. cruzi), and phlebotomine sandflies (Leishmania).

Morphology varies: Trypanosoma species cycle between slender bloodstream forms in mammals and thicker procyclic forms in the insect vector; Leishmania species exist as intracellular amastigotes within vertebrate macrophages and as flagellated promastigotes in the insect gut.

Genomes and gene expression are organized polycistronically, with mitochondrial transcripts undergoing RNA editing in many species, notably in T. brucei. The group includes genera such as Trypanosoma, Leishmania, Phytomonas, Crithidia, and Leptomonas, among others; many trypanosomatids are parasites, while others inhabit plants or invertebrates without causing disease.

Understanding their biology informs disease control, diagnostics, and basic cellular biology, with Trypanosoma brucei and Leishmania spp. serving as important model organisms in parasitology and molecular biology.