Despite the considerable public health burden of Lyme disease and the recent demonstration that arthropod microbiomes can impact vector competence, little is known about the effect of the tick microbiome on tick competence for the Lyme disease bacterium, Borrelia burgdorferi. Here, we investigate the role of the microbiome of Ixodes pacificus, the primary vector of Lyme disease in the Western US, on B. burgdorferi acquisition. We used known blood meal-driven microbiome differences in I. pacificus, namely lizard-feeding or rodent-feeding, to generate naturally low or high levels of microbiome diversity, respectively. We allowed larval ticks to feed fully on one of these two hosts, molt to the nymphal life stage, and then feed on a rodent infected with B. burgdorferi. For all ticks that successfully engorged on the infectious blood meal, we measured the B. burgdorferi infection prevalence and loads using quantitative PCR. This set-up allowed us to examine the relationship between tick microbiome diversity and infection rates in an ecologically-relevant manner, as lizards and rodents are common tick hosts in California.
Results/Conclusions
I. pacificus nymphal ticks that fed on B. burgdorferi positive mice were significantly more likely to become infected if they had previously fed on lizards as larvae than if they had previously fed on rodents. Infected lizard-group nymphs also had ten-fold higher B. burgdorferi loads than infected rodent-group nymphs. Taken together, we found that I. pacificus microbiome diversity and pathogen acquisition were negatively associated, a result which contradicts previous work on I. scapularis, the East coast Lyme disease vector. These contrasting results, as well as an overall dearth of research on the role of tick microbiomes, highlight a substantial need for further investigation into the mechanisms governing interactions between the tick microbiome and pathogen transmission dynamics. Elucidating these mechanisms through experiments focused on ecologically-relevant manipulations of the tick microbiome is a critical future direction in this field necessary for applying these results in the prevention and control of tick-borne disease.