Trypanosoma brucei gambiense life cycle.
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1. During a blood meal on a mammalian host, an infected tsetse fly injects metacyclic trypomastigotes into skin tissue. The parasites enter the lymphatic system and pass into the bloodstream.
2. Inside the host, they transform into bloodstream trypomastigotes, are carried to other sites throughout the body, and enter other blood fluids (eg, lymph, spinal fluid).
3. The trypomastigotes multiply by binary fission.
4. They circulate in the bloodstream.
5. During a blood meal on an infected mammalian host, a tsetse fly becomes infected with bloodstream trypomastigotes.
6. In the fly's midgut, the parasites transform into procyclic trypomastigotes and multiply by binary fission.
7. The procyclic trypomastigotes leave the midgut and transform into epimastigotes.
8. The epimastigotes reach the fly's salivary glands, multiply by binary fission, and develop into metacyclic trypomastigotes.
Image from the Centers for Disease Control and Prevention Image Library.