Study design. Phase 1: On day 0, two rhesus macaques were inoculated with erythrocytes containing 6×109 hamster-passaged B. microti. In phase 2, three monkeys were transfused with 1.5×107 monkey-passaged B. microti obtained on day 56 of phase 1. One monkey in phase 3 was transfused with 25,000 monkey-passaged B. microti acquired from a phase 2 monkey. All animals in this study were treated with atovaquone and azithromycin for 10 days starting on day 122. Phase 1 and 3 animals received a second course of treatment starting on days 193 and 200, respectively. Blood samples for PCR, IFA, flow cytometry and ear prick for blood smear examination were collected at multiple time points during the three phases of the study.