Rickettsia slovaca in immature Dermacentor marginatus and tissues from Apodemus spp. in the northern Apennines, Italy

Immature Dermacentor marginatus ticks and tissues from small rodents were tested for infection with Rickettsia slovaca in the northern Apennines, Lucca Province, where tick-borne lymphadenopathy (TIBOLA) was previously reported in people. Prevalence of infestation with D. marginatus was 30.5% (n = 131, 95% CI: 22.8–39.2%) in Apodemus spp. and 26.5% (n = 34, 95% CI: 12.9–44.4%) in Myodes glareolus, which were captured during 1980 trap nights in 2009 and 2010. Rickettsia slovaca was identified by polymerase chain reaction, targeting the gltA and OmpA genes, in ear biopsies from 8 out of 37 tested Apodemus (22%, 95% CI: 9.8–38.2%), but not from 9 M. glareolus. The prevalence of R. slovaca in D. marginatus feeding on Apodemus spp. was 53% in larvae (n = 51, 95% CI: 38.5–67.1%) and 47.5% in nymphs (n = 59, 95% CI: 34.3–60.9%). No larvae (0.0%, 95% CI: 0–36.9%), but one nymph removed from M. glareolus was positive (10%, 95% CI: 0.3–44.5%). Prevalence of R. slovaca in host-seeking D. marginatus larvae, collected in the same area, was 42% (n = 38; 95% CI: 26.3–59.2%). Prevalence of R. slovaca was greater in larvae feeding on PCR-positive Apodemus than in those feeding on negative mice (78.6% vs. 37.1%). Furthermore, levels of infestation with D. marginatus larvae were greater for R. slovaca-positive mice. The infection of Apodemus spp. was probably the result of repeated bites by transovarially infected larvae. On the other hand, the finding of R. slovaca in mice tissues would be compatible with transmission from these hosts to feeding D. marginatus. Based on such a hypothesis, the most heavily infested Apodemus might play a role as amplifiers of the infection.