Bartonella infections are prevalent in rodents despite efficient immune responses

Pathogens face strong selection from host immune responses, yet many host populations support pervasive pathogen populations. We investigated this puzzle in a model system of Bartonella and rodents from Israel’s northwestern Negev Desert. We chose to study this system because in this region, 75–100% of the rodents are infected with Bartonella at any given time, despite an efficient immunological response. In this region, Bartonella species circulate in three rodent species, and we tested the hypothesis that at least some of these hosts exhibit a waning immune response to Bartonella, which allows reinfections. To that end, we inoculated captive rodents from all three species with the same Bartonella strain, and we quantified the bacterial dynamics and Bartonella-specific IgG antibody kinetics through 139 days after the primary inoculation and then for 60 days following re-inoculation with the same strain. Contrary to our hypothesis, we found a strong, long-lasting IgG antibody response, with a protective immunological memory in all three rodent species. That response prevented re-infection upon exposure to the same Bartonella strain. This study constitutes an initial step toward a better understanding of the interplay between Bartonella pathogens and rodent traits, and how the interplay of those traits influences epidemiological dynamics in nature.