The life cycle of Trypanosoma brucei occurs in both tsetse flies and humans. When an infected tsetse fly feeds on a human, it injects the parasite into the bloodstream, where it multiplies by binary fission in the blood, lymph, and spinal fluid. When another tsetse fly feeds on the infected host, it ingests the parasites, which then multiply by binary fission in the fly's midgut before transforming into an infectious stage that colonizes the salivary glands.