Trypanosoma brucei

''Trypanosoma brucei'' is a species of parasitic kinetoplastid belonging to the genus ''Trypanosoma''. This parasite is the cause of vector-borne diseases of vertebrate animals, including humans, carried by species of tsetse fly in sub-Saharan Africa. In humans ''T. brucei'' causes African trypanosomiasis, or sleeping sickness. In animals it causes animal trypanosomiasis, also called nagana in cattle and horses. ''T. brucei'' has traditionally been grouped into three subspecies: ''T. b. brucei'', ''T. b. gambiense'' and ''T. b. rhodesiense''. The first is a parasite of non-human vertebrates, while the latter two are known to be parasites of humans. Only rarely can the ''T. b. brucei'' infect a human.

''T. brucei'' is transmitted between mammal hosts by an insect vector belonging to different species of tsetse fly . Transmission occurs by biting during the insect's blood meal. The parasites undergo complex morphological changes as they move between insect and mammal over the course of their life cycle. The mammalian bloodstream forms are notable for their cell surface proteins, variant surface glycoproteins, which undergo remarkable antigenic variation, enabling persistent evasion of host adaptive immunity leading to chronic infection. ''T. brucei'' is one of only a few pathogens known to cross the blood brain barrier. There is an urgent need for the development of new drug therapies, as current treatments can have severe side effects and can prove fatal to the patient.

Whilst not historically regarded as ''T. brucei'' subspecies due to their different means of transmission, clinical presentation, and loss of kinetoplast DNA, genetic analyses reveal that ''T. equiperdum'' and ''T. evansi'' are evolved from parasites very similar to ''T. b. brucei'', and are thought to be members of the ''brucei'' clade.

The parasite was discovered in 1894 by Sir David Bruce, after whom the scientific name was given in 1899.