Answer: Trypanosoma brucei trypomastigotes in peripheral blood.
Trypanosoma brucei is only present in humans as trypomastigotes (motile stages with flagella) in blood, unlike the other human trypanosome, T. cruzi, which can form both trypomastigotes AND non-motile tissue amastigotes in humans. As noted by Anon and Florida Fan, the trypomastigotes of Trypanosoma brucei divide by binary fission in the peripheral blood, as seen in this case, thus allowing the organism to replicate in humans. In contrast, T. cruzi trypomastigotes do not divide in blood - it is the amastigote form that divides by binary fission.
Note the trypomastigote that is preparing to divide by replicating its internal structures:
Here is a trypomastigote which has almost completely divided:
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