Laboratory study design.

<p><i>Peromyscus leucopus</i> mice were infected with <i>Babesia microti</i> alone (Group 1 [8 mice]) or coinfected with <i>B. microti</i> and one of two strains of <i>Borrelia burgdorferi:</i> BL206 (Group 2 [3 mice]) or B348 (Group 3 [8 mice]). Xenodiagnosis was performed at 7, 14, 21, 28, 42 days. <i>B. microti</i> infection was determined in ticks at 7, 14, 21, 28, 42 days by qPCR. <i>B. microti</i> infection was determined in mouse blood at weeks 7, 14, 28, 42 days by flow cytometry.