African trypanosomiasis, or 'sleeping sickness', a serious infection caused by the protozoan Trypanosoma brucei, is usually spread to humans by the tsetse flies infected by animals and other humans. Photo credit: CDC/Dr. Mae Melvin This is a micrograph of a rat blood smear revealing Trypanosoma brucei parasites, using a Giemsa stain technique. African trypanosomiasis, or “sleeping sickness”, a serious infection caused by the protozoan Trypanosoma brucei, is usually spread to humans by the tsetse flies infected by animals and other humans.