Midichloria mitochondrii: a novel tick-borne infectious agent?

Ixodes ricinus is a vector of various pathogens, and the most widespread tick in Europe. I. ricinus also harbors the Rickettsiales bacterium Midichloria mitochondrii, which is present in 100% females and in ~50% males. Most M. mitochondrii bacteria are localized in the cells of the ovary, either in the cytoplasm or within the outer membrane of mitochondria. M. mitochondrii is vertically transmitted from the tick mother to the offspring; however horizontal transmission, possibly through the host blood, cannot be excluded a priori. We used a multidisciplinary approach to uncover possible transmission of M. mitochondrii to humans and other tick hosts.