Answer: Trypomastigotes and intermediate trypomastigote/amastigote forms of Trypanosoma cruzi.
Thanks to everyone who wrote in for this case! This was, admittedly, a tricky case, since it is uncommon to see amastigote-type forms in peripheral blood. The reason these atypical forms were present is because this specimen was grown in culture and then innoculated in peripheral blood (artificial infection). Fortunately, the classic "C-shaped" trypomastigote forms with large kinetoplast were still abundant and allowed accurate identification. Although you wouldn't expect to see a case like this in nature, this type of preparation may show up on proficiency test (since this material is typically grown in culture). Another important point of this case is that the forms on the thick smear resemble Plasmodium rings; thus, it is always important to examine BOTH the thick and thin smears!