Studies on the Distribution of Japanese Strain of Spotted Fever Group Rickettsiae in China

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Infections with Rickettsia Japonica, a newly identified spotted fever group (SFG) rickettsia, were recognized mostly in the southwestern part of Japan facing the Pacific Ocean. It has been known that the various species of SFG rickettsiae occur in geographically distinct regions (biogeographic regions) separated for the most part by natural boundaries. The present study was designed to find the distribution of R. japonica in the Oriental region. Serologic surveys for antibodies to R. Japonica were conducted on Hainan Island in the southern part of China and also in Shandong Province of the eastern edge. Total of 499 serum specimens were collected from hospitals located in the northern, eastern, central, western, and southern parts of Hainan Island. Only one among 107 serum specimens collected in the southern part was found to contain antibodies reactive with R. Japonica at a high titer. Further survey also showed that one out of 331 serum specimens collected in the southern Hainan Island contained antibodies reactive with R. Japonica. The results indicated a possibility of the existence of a SFG rickettsiosis on the island, although its incidence seems to be very low. R. Japonica is likely to be a candidate for the causative agent, but the positive proof needs to isolate and identify the agent. Up to the present, the isolation of a SFG rickettsia has been performed without success. The present study also demonstrated a high incidence of murine typhus on Hainan Island. About 2.7 to 12% of serum specimens collected in the southern part reacted with R. Typhi, a half of which contained IgM antibodies, Furthermore, more than 60% of suspected rickettsial infections were murine typhus. In Shandong province, on the other hand, 1100 serum specimens were tested, demonstrating that 3 among 500 specimens from a hospital in Jinan city contained low titers of antibodies reactive with R. Japonica.