It is a parasitic flagellate inhabiting the blood and other fluids of all groups of vertebrates from fishes to mammals. It is transmitted to them by blood sucking invertebrates like insects and leeches.
The adult trypanosoma consists of a fusiform body pointed at both ends. A single oral nucleus is present in the center.
There is a single flagellum arising from a minute granule, the blepharoplast, near the posterior end of the body. Near the blepharoplast, there is a large body called the kinetoplast. There is a thin irregular rippling fold called the undulating membrane along one of the margins of the body. The flagellum extends forwards along the free edge of the undulating membrane and then projects freely in front of the body.
Reproduction occurs by longitudinal binary fission.
Several species of Trypanosoma are pathogenic to man and domestic animals. T. gambiense causes sleeping sickness in man. The parasite first lives in the blood and then enters the cerebrospinal fluid of the brain and spinal cord. The blood sucking tse- tse flies (Glossina palpalis) act as vectors.