Borrelia burgdorferi strain and host sex influence pathogen prevalence and abundance in the tissues of a laboratory rodent host

Experimental infections with different pathogen strains give insight into
pathogen life history traits. The purpose of our study was to compare
variation in tissue infection prevalence and spirochete abundance among
strains of B. burgdorferi in a rodent host (Mus musculus, C3H/HeJ). Male
and female mice were experimentally infected via tick bite with one of 12
strains. Ear tissue biopsies were taken at days 29, 59, and 89
post-infection (PI), and 7 tissues were collected at necropsy. The
presence and abundance of spirochetes in the mouse tissues were measured
by qPCR. To determine the frequencies of our strains in nature, their
MLSTs were matched to published datasets. For the infected mice, 56.6% of
the tissues were infected with B. burgdorferi. The mean spirochete load in
the mouse necropsy tissues varied 4.8-fold between the strains with the
lowest and highest values. The mean spirochete load in the ear tissue
biopsies decreased rapidly over time for some strains. The percentage of
infected tissues in male mice (65.4%) was significantly higher compared to
female mice (50.5%). The mean spirochete load in the 7 tissues was 1.5x
higher in male mice compared to female mice; this male bias was 15.3x
higher in the ventral skin. Across the 11 strains, the mean spirochete
loads in the infected mouse tissues were positively correlated with the
strain-specific frequencies in their tick vector populations. Our study
suggests that laboratory-based estimates of pathogen abundance in host
tissues can predict the strain composition of this important tick-borne
pathogen in nature.