Sleeping sickness. Light micrograph of Trypanosoma brucei parasites, a cause of sleeping sickness, in blood. The long thin T. brucei cells (dark blue) can be seen amongst stacks of red blood cells. These parasitic protozoa, or single-celled organisms, occur in tropical Africa, and are spread to humans by the bite of the tsetse fly (Glossina sp.). Symptoms of sleeping sickness include headaches, confusion and severe tiredness. Unless treated with drugs, coma and death will result. Phase contrast. Magnification unknown.