Associate Professor Yale University New Haven, Connecticut
We summarize our observations on the role of the microbiome of Ixodes scapularis, the predominant vector of Borrelia burgdorferi, the agent of Lyme disease, in B. burgdorferi transmission to the vertebrate host. Earlier work has demonstrated that environmental bacteria associate with I. scapularis and influence B. burgdorferi colonization of the tick midgut. There has been speculation about the role of environmental microbiota on B. burgdorferi migration from the tick to the mammalian host. To examine this, we perturbed the microbiome of B. burgdorferi-infected nymphs by raising ticks in germ-free isolators, by antibiotic treatment or by downregulating immune pathways of the tick gut. Our observations suggest that environmental bacteria do not influence spirochete growth in and migration from the midgut and consequently has no significant impact on transmission to the murine host. Providing a possible explanation for this, we present transmission electron microscopic images of the tick midgut that suggest an intracellular and potentially unique route of B. burgdorferi egress from the gut. The intracellular route of migration that appears to begin within 24 hours of tick feeding could allow the spirochete to escape direct or indirect interactions with luminal microbiota. Our observations highlight the need to better understand this process of B. burgdorferi egress- an event essential for transmission to the mammalian host. These observations would help redirect research in this field, both in the context of the tick microbiome and in the context of spirochete biology to spawn new paradigms to prevent tick-transmission of B. burgdorferi.
