Coloured scanning electron micrograph (SEM) of Trypanosoma brucei parasites (blue) and a red blood cell. T. brucei is a protozoan and the causative agent of African sleeping sickness. It is transmitted to humans via the bite of the tsetse fly. Initial infection causes fever, joint pain and itching. Once the parasite has crossed into the central nervous system it causes confusion, disturbance of the sleep cycle and reduced coordination. Without treatment African sleeping sickness is fatal.