Trypanosomes are unicellular, flagellated protozoan organisms, forming part of the order "Kinetoplastida". The order is charachterised by the presence of one flagellum and a single mitochondrion containing the "kinetoplast", a specialized DNA containing organelle. Species of the parasite colonise vertebrates, invertebrates and plants. Some species are pathogenic, causing disease in humans and their domestic animals. Amongst these are T. cruzi, causative agent of Chagas' disease in South America, and T. brucei spp. causing African Trypanosomiasis (also known as Sleeping sickness) and the cattle wasting disease nagana in sub-Saharan Africa. Transmission of the human-infective trypanosome spp. is via blood feeding insects.

Throughout its life cycle, the parasite alternates between development in mammalian tissue fluids and bloodstream as well as growth in its vector's (the Tsetse) midgut and salivary gland. Development is accompanied by changes in morphology, biochemistry, cell cycle stage and expression of major surface markers.

The pictures below [kindly made available by Dave Barry (University of Glasgow) and Markus Engstler (Ludwig-Maximilians-Universitaet, Muenchen)] shows images generated by scanning electron microscopy of some of the parasite's life cycle stages (left image) and a cartoon of a T. brucei cell (right image). Clicking on a particular image will spawn a new window with an enlarged picture.