Abstract
White-footed mice (Peromyscus leucopus) serve as the principal reservoir for Borrelia burgdorferi and have been shown to remain infected for life. Complex infections with multiple genetic variants of B. burgdorferi occur in mice through multiple exposures to infected ticks or through exposure to ticks infected with multiple variants of B. burgdorferi. Using a combination of cloning and single strand conformation polymorphism (SSCP), B. burgdorferi ospC variation was assessed in serial samples collected from individual P. leucopus during a single transmission season. In individuals with ospC variation, at least seven ospC variants were recognized at each time point. One to four of these variants predominated at each time point; however, the predominant variants seldom remained consistent in an individual mouse throughout the entire sampling period. These results confirmed that mice in southern Maryland were persistently infected with multiple variants of B. burgdorferi throughout the transmission season. However, the presence of multiple ospC variants and the fluctuations in the frequency of these variants indicates that either new ospC variants are regularly introduced to this mouse population and predominate while the existing infections are cleared, or that the variation detected in the genetic profile at different time points reflects a complex mixture of B. burgdorferi populations whose relative frequencies may continually change.