STRAIN VARIATION OF RICKETTSIA ORIENTALIS IN THE COMPLEMENT FIXATION TEST*

Abstract
In the serological classification of strains of Rickettsia orientalis by the complement-fixation test presented in this paper,it should be pointed out that some strains gave much more cross-reaction compared with prototype strains of Kato, Karp, and Gilliam. However, it may be justified to classify a number of strains into 3 types according to their main antigen, if the classification were used not for the purpose of antigenic analysis of each strain but for obtaining such a general idea of epidemiological status of scrub typhus in Japan as will be described later. In this sense, it will be also justified to classify antigehicity of strains in the complement fixation test by a one-way method, that is, by analysis of antibody pattern of strain-specific immune serum of each strain against three types of antigen without testing its antigenicity in antigen prepared from each strain. Kato type strains were isolated from human cases of the classic type of scrub typhus, Trombicula akamushi, and from field rodents captured in Niigata, an endemic area of this type of the disease. This may reasonably justify use of Kato strain, which was isolated from a patient in Niigata and adapted to the yolk sac tissue in this laboratory, as a reference strain of R. orientalis (Shishido et al., 1958). In other words, the finding that strains of this type were frequently isolated from T. akamushi as well as from field rodents in Niigata will be a good indication that Kato type strain will respresent a prevalent type of the classic scrub typhus in Japan. Karp type strains were isolated from human cases of the new type of scrub typhus, T. pallida, Eushoengastia ikaoensis, and also from rodents captured throughout Japan including new endemic foci of the disease. This means that the agent causing a new type of the disease seems to be the Karp type. As to the vector of the new type of scrub typhus, T. scutellaris and T. pallida were already reported to be a potential one in Izu Islands (Sasa, 1954) and Chiba Prefecture (Asanuma et al., 1959) and that at Miura, Kanagawa Prefecture and Shimoda, Shizuoka Prefecture (Asanuma et al., 1960) respectively. However, no strain from T. scutellaris was available to test for the type it belongs to in this experiment, therefore a serological confirmation of the vector of T. scutellaria was not accomplished as yet, and the role of E. ikaoensis on the vector of the scrub typhus at Fuji remained to be determined in a further epidemiological investigation. Moreover, it was neither clarified as yet what species of trombiculid mite are taking a potential role in the distribution of Karp type rickettsia among the field rodents throughout Japan. Gilliam type strains were isolated from T. pallida in Niigata, T. kawamurai in Hokkaido, and rodents captured at both the places. There is no case of scrub typhus, either classic or new type, from which a Gilliam type strain was isolated. If a case can be found in Hokkaido in the future, it might be highly probable that it is caused by the Gilliam type agent, and if a case occurs by attack of T. pallida infected with R. orientalis in Niigata, it will be caused by the Gilliam type.