[Sequence analysis subtyping of the 56-kDa protein-encoding gene of Karp-type Orientia tsutsugamushi isolated in scrub typhus cases].

To determine the Karp-type Orientia tsutsugamushi subtype in northern Japan, i.e., Yamagata, Niigata, and Akita Prefectures, we analyzed the partial nucleotide sequence of the 56-kDa protein-encoding gene of 30 isolates from scrub typhus cases. Based on sequencing results, we classified isolates into two groups of 27 and 3 isolates. Nucleotide sequences of 27 isolates were homologous to the yeo-joo strain, classified as a JP-1 subtype. The three isolates were each homologous to a stain of CMM1, KNP1, or KNP2, classified as JP-2 subtypes. Phylogenetic tree analysis showed the 27 isolates forming a cluster with the yeo-joo strain and the three isolates with the CMM, KNP1, and KNP2 strains and therefore belonging to these subtypes. The Karp-type O. tsutsugamushi JP-2 subtype predominates in Japan, the JP-1 subtype probably the predominates in the area investigated. O. tsutsugamushi JP-1 subtype strains must therefore be isolated from subjects in this area and comprehensively studied.