In further agreement with earlier reports showing increased expression of type IV secretion components and putative effectors of R. rickettsii in tick vectors during blood meal [8], we also observed up-regulation of transcripts encoding for VirB6, VirB8, and VirB9, ankyrin repeat proteins (Ank proteins), tetratricopeptide repeat proteins (TPR), acid phosphatase, and metalloprotease during tick cell infection (Additional file 2). Here, TPR is linked to infection.