Evolution of antigenic diversity in the tick-transmitted bacterium Borrelia afzelii: a role for host specialization?

Antigenic diversity in pathogenic microbes can be a result of at least three different processes: diversifying selection by acquired immunity, host-pathogen coevolution, and/or host specialization. Here, we investigate if host specialization drives diversity at ospC (which encodes an immunodominant surface protein) in the tick-transmitted bacterium Borrelia afzelii. We determined prevalence and infection intensity of ospC strains in naturally infected wild mammals (rodents and shrews) by 454 amplicon sequencing in combination with qPCR. Neither prevalence nor infection intensity of specific ospC strains varied in a species-specific manner (i.e. there were no significant ospC × host species interactions). Rankings of ospC prevalences were strongly positively correlated across host species. Rankings of ospC infection intensities were correlated more weakly, but only in one case significantly less than 1. ospC prevalences in the studied mammals were similar to those in ticks sampled at the...