Phylogenetic Analysis of Spotted Fever Group Rickettsiae Isolated from Ticks in Japan

Eight spotted fever group (SFG) rickettsiae isolated from ticks in Japan were classified by phylogenetic analysis based on the nucleotide sequences of both the citrate synthase‐encoding gene (gltA) and 190‐kDa antigen‐encoding gene (rOmpA). In the phylogenetic tree of gltA, strains DT‐1 and FLA‐1 isolated from the Dermacentor taiwanensis and Haemaphysalis frava ticks, respectively, were placed as Rickettsia japonica, and strains IO‐1, IO‐2, IO‐25, IM‐1 and IP‐2 from genus Ixodes ticks were placed as Rickettsia helvetica. Strain AT‐1 isolated from the Amblyomma testudinarium belonged to the cluster including Rickettsia akari, Rickettsia australis and Rickettsia felis. In the phylogenetic tree of the rOmpA, strains DT‐1 and FLA‐1 were placed as R. japonica, and strain AT‐1 belonged to the cluster including Rickettsia cooleyi and the symbiont of Ixodes scapularis. The rOmpA fragments of 5 Ixodes isolates could not be amplified by PCR. The present study showed that strains DT‐1 and FLA‐1 were genotypically identical to R. japonica, and 5 Ixodes isolates were associated with the R. helvetica. Based on previous genotypic and antigenic data, and the phylogenetic analysis presented here, strain AT‐1 should be considered as a new species among SFG rickettsiae.