Epidemiological survey of Orientia tsutsugamushi distribution in field rodents in Saitama Prefecture, Japan, and discovery of a new type

There are various antigenic variants of Orientia tsutsugamushi which are di stinguished by immunological and molecular genetic methods targeted at the antigenic diversity of 56-kDa type-specific antigen proteins. The present s tudy was performed to analyze 15 strains successfully isolated from rodents in Saitama Prefecture, Japan, by 56-kDa gene sequence homologies, reactivi ties with type-specific monoclonal antibodies and polymerase chain reaction (PCR) using type-specific primer-pairs. We demonstrated the presence of a new type of O. tsutsugamushi among the isolates. This new type, designated as the Saitama type, was located in the branch of Karp type in the phylogen etic tree based on 56-kDa gene sequences, but distant from the known Karp t ypes, such as Karp, JP-1 and JP-2, showing less than 90% homology, Strains of this type could not be distinguished by immunological methods from Karp type strains, but a new primer-pair for PCR which specifically amplifies th e DNA of this new type strain was designed, This primer-pair may serve to f ind this strain type in future studies.