Schematic drawing of the tsetse fly, the biological vector of the Trypanosoma parasite. During the feeding process, the parasite is transmitted by the fly from infected to uninfected vertebrate hosts. After uptake of the trypanosomes from an infected human, the parasite reproduces itself within the tsetse fly, representing the sexual phase of the trypanosome life cycle. This image relates to a paper that appeared in the November 29, 2012, issue of Science Express, published by AAAS. The paper, by Lars Redecke at the University of Hamburg in Hamburg, Germany, and colleagues was titled, "Natively Inhibited Trypanosoma brucei Cathepsin B Structure Determined Using an X-ray Laser."