Epidemiological Survey on the Tsutsugamushi Disease in Taiwan, in Connection with its High Prevalence in Recent Japan

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Besides the classical summer type of tsutsugamushi disease, Japan has a new type which occurs mainly in spring and autumn. The latter has increased sharply since 1976 in various parts of Japan and becomes a serious problem. On the other hand, a resurgence of the disease is known in the Southeast Asian Region. The purpose of this field research is to obtain several common epidemiological factors of tsutsugamushi disease in Taiwan located between those northern and southern regions.1. The reported cases (confirmed cases) of tsutsugamushi disease in Tawian were 660 (340) for 6 years (1985-1990) but fatal cases were only 2. Most of the patients occurred between May to November, showing the main peak of June to July and small one of October.2. The reactivities of 426 sera collected from inhabitants of the whole island were examined by indirect fluorescent antibody test and immunoperoxidase test using 3 prototype strains of tsutsugamushi disease, and 54.9% were positive among them. The relatively low specificity in the reactivity to 3 prototypes and also to the low-virulent strains isolated in Japan were obtained, indicating that Rickettsia tsutsugamushi in Taiwan might have antigenic properties distinctive from Japanese strains.3. In the level lands and low hills 7 species of trombiculids were collected from small mammals and Leptotrombidium (L.) deliense, main vector of the disease, was predominant, occupying over 90% of the total number of them. On Mt. Alishan, 7 species of trombiculids were collected, but L. (L.) deliense was not detected. L. (L.) asanumai, which is close to L. (L.) scutellare, one of the main vectors of Japanese new type tsutsugamushi disease, was collected. Rickettsia tsutsugamushi was isolated from 6 wild rodents and 2 L. (L.) deliense, and their polypeptide composition and antigenic componentsare now being examined in detail.