Similar to previous experiments, we quantified the mean number of viable spirochetes per tick in cohorts of infected nymphs fed upon naïve, heterologously and homologously infected Rag1 KO mice and found that the infection status of the blood-meal host did not affect the spirochete burden in any group of ticks (~ 3–5 x104 CFU/tick) (Fig 4). Here, RAG1 is linked to infection.