trypomastigote

A trypomastigote is a morphological stage of certain kinetoplastid protozoa, most notably Trypanosoma species. It is a slender, elongated cell characterized by a single nucleus, a long flagellum that emerges from the front end, and an attached undulating membrane that extends along much of the cell length. A defining feature is the kinetoplast, a circular network of mitochondrial DNA, located posterior to the nucleus in this form.

In the parasite life cycle, trypomastigotes are typically the flagellated, infective forms found in the blood or tissue fluids of vertebrate hosts. In many species, mammalian-stage trypomastigotes circulate extracellularly and are taken up by insect vectors during a blood meal. Within the vector, they transform into other stages that continue development before returning to the vertebrate host to complete the cycle.

Two well-known pathogenic examples are Trypanosoma brucei, which causes African sleeping sickness, and Trypanosoma cruzi, the agent of Chagas disease. In T. brucei, bloodstream trypomastigotes evade immune responses through antigenic variation of the variant surface glycoprotein. In T. cruzi, bloodstream trypomastigotes invade host cells and differentiate into intracellular amastigotes.

Microscopic identification relies on observing the elongated cell with a posterior kinetoplast and an anterior flagellum with an undulating membrane; additional stains or molecular methods may aid detection in clinical samples.