Spirochete burdens as assessed by (A) colony counts (mean ± SEM) and (B) qPCR in midguts of larvae naturally fed on mice infected with wt, oppA1tn, and oppA1c. Each data point represents a separate pool of larvae. (C) Detection of spirochetes by immunofluorescence analysis of midguts from replete larvae fed on mice infected with wt, oppA1tn, or oppA1c (400x total magnification). Spirochete burdens (mean ± SEM) assessed by (D) colony counts and (E) qPCR in midguts of larvae immersed in wt, oppA1tn, or oppA1c cultures and subsequently fed on naïve C3H/HeJ. Each data point represents a separate pool of larvae. Statistical analysis of tick studies was determined by unpaired Student’s t test.