Trypanosoma brucei is a parasitic protist that causes significant health burden in sub-Saharan countries endemic for the tsetse fly (Glossina spp.). During the bloodmeal of this insect vector, the flagellate is transmitted to a variety of mammals, including humans, in which T. brucei subs. gambiense and T. brucei subs. rhodesiense cause human African trypanosomiasis.
During its life cycle, T. brucei encounters and adapts to very diverse environments that differ in available nutrients. In the mammalian host, it exists in two major forms: the replicating long-slender bloodstream form (LS-BSF) and the nondividing short-stumpy bloodstream form (SS-BSF), the latter being pre-adapted to infect the insect vector.