eLife Assessment
The manuscript concerns a fundamental and controversial question in Trypanosoma brucei biology and the parasite life cycle, providing further evidence that slender bloodstream forms can indeed infect Tsetse flies. The study is solid in design and execution, and addresses several criticisms made of the authors' earlier work. Nevertheless, some of the main conclusions are only partially supported: one issue is how, precisely, a "slender" bloodstream form is defined, and discrepancies with some results from other laboratories remain unexplained.