title: Humans parasitized by the hard tick Ixodes ricinus are seropositive to Midichloria mitochondrii: is Midichloria a novel pathogen, or just a marker of tick bite?
abstract: Midichloria mitochondrii is an intracellular bacterium found in the hard tick Ixodes ricinus. In this arthropod, M. mitochondrii is observed in the oocytes and in other cells of the ovary, where the symbiont is present in the cell cytoplasm and inside the mitochondria.  No studies have so far investigated whether M. mitochondrii is present in the salivary glands of the tick and whether it is transmitted to vertebrates during the tick blood meal. To address the above issues, we developed a recombinant antigen of M. mitochondrii (to screen human  sera) and antibodies against this antigen (for the staining of the symbiont). Using these reagents we show that (i) M. mitochondrii is present in the salivary glands of I. ricinus and that (ii) seropositivity against M. mitochondrii is highly prevalent in humans parasitized  by I. ricinus (58%), while it is very low in healthy individuals (1·2%). These results provide evidence that M. mitochondrii is released with the tick saliva and raise the possibility that M. mitochondrii is infectious to vertebrates. Besides this, our study indicates  that M. mitochondrii should be regarded as a package of antigens inoculated into the human host during the tick bite. This implies that the immunology of the response toward the saliva of I. ricinus is to be reconsidered on the basis of potential effects of M. mitochondrii  and poses the basis for the development of novel markers for investigating the exposure of humans and animals to this tick species.
authors.affiliation: Dipartimento di Scienze Veterinarie e Sanità Pubblica, Università degli Studi di Milano, Milano, Italy.
authors.forename: Mara
authors.initials: M
authors.lastname: Mariconti
authors.forename: Sara
authors.initials: S
authors.lastname: Epis
authors.forename: Paolo
authors.initials: P
authors.lastname: Gaibani
authors.forename: Claudia
authors.initials: C
authors.lastname: Dalla Valle
authors.forename: Davide
authors.initials: D
authors.lastname: Sassera
authors.forename: Paola
authors.initials: P
authors.lastname: Tomao
authors.forename: Massimo
authors.initials: M
authors.lastname: Fabbi
authors.forename: Francesco
authors.initials: F
authors.lastname: Castelli
authors.forename: Piero
authors.initials: P
authors.lastname: Marone
authors.forename: Vittorio
authors.initials: V
authors.lastname: Sambri
authors.forename: Chiara
authors.initials: C
authors.lastname: Bazzocchi
authors.forename: Claudio
authors.initials: C
authors.lastname: Bandi
mesh_terms: D020561:Alphaproteobacteria / Q000276:immunology / Q000302:isolation & purification* / Q000472:pathogenicity; D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D001424:Bacterial Infections / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology; D005260:Female; D006801:Humans; D007299:Insect Bites and Stings / Q000150:complications*; D018884:Ixodes / Q000382:microbiology / Q000472:pathogenicity*; D012469:Salivary Glands / Q000382:microbiology; D016036:Seroepidemiologic Studies; D017282:Tick-Borne Diseases / Q000175:diagnosis* / Q000453:epidemiology / Q000382:microbiology
chemical_list: D000907:Antibodies, Bacterial