Borrelia burgdorferi sensu lato and spotted fever group rickettsiae in small rodents and attached ticks in the Northern Apennines, Italy

Ticks and ear biopsies were collected from wild small rodents in 2011 and 2012 in the northern Apennines (Italy), up to 1650m above sea level. Apodemus spp. (n=83) and Myodes glareolus (n=22) were infested by Ixodes ricinus (192 larvae and two nymphs), Dermacentor marginatus (179 larvae and 29 nymphs), and Ixodes trianguliceps (three larvae and two nymphs). We detected several Borrelia burgdorferi sensu lato (s.l.) genospecies (B. afzelii, B. burgdorferi sensu stricto, B. garinii, B. lusitaniae, B. valaisiana) in I. ricinus and skin biopsies. The most common genospecies found in I. ricinus was B. valaisiana, while it was B. lusitaniae in tissues. Spotted fever group (SFG) rickettsiae (Rickettsia monacensis, R. slovaca and R. raoultii) infected I. ricinus, D. marginatus and rodent tissues. Rickettsia slovaca was the Rickettsia species most frequently found in our samples. Coinfections by B. burgdorferi s.l. and SFG rickettsiae indicate an overlap of transmission cycles and potential risk for humans to be infected by multiple pathogens, resulting in more severe symptoms. The findings of B. lusitaniae and R. slovaca in bank voles, and of B. valaisiana in small rodents, open new questions about host-pathogen interactions. In addition, our results highlight the importance of small rodents as data sources for studying tick-borne pathogens.