T. brucei subspecies are transmitted to mammalian hosts by the bite of tsetse flies (Glossina spp.). A tsetse fly gets infected when taking a bloodmeal on an infected mammalian host. A complex developmental cycle in the fly ends with the infective metacyclic stage in the lumen of the salivary glands (Figure 75.7). This process may take 3–4 weeks. Metacyclic trypanosomes are injected into the skin of the mammalian host during the probing and feeding process. Development in the tsetse fly involves a complex series of changes in the morphology and biochemistry of the parasite. Several factors play key roles in these changes: lectins present in Glossina midgut and haemolymph, the presence of Rickettsia-like organisms, and molecular signals that influence parasite transformation, establishment and maturation.^[46]Lectins in the tsetse midgut kill incoming trypanosomes. Feeding lectin-inhibitory sugars or procyclin to flies significantly increased the midgut infection rates. While …