Epidemiological Studies on the Leptospirosis in Okinawa : Part 1. Prevalence of the Leptospirosis in Izena Island and the Prevention by Vaccination

Inhabitants of Izena, a small island about 27 kilometers away from Okinawa main island, were inspected for the status of anti-leptospira antibody in spring, 1971. About 30% of the age group from higher classes of primary school to junior high school and about 50% of adults were found to be anti-leptospira antibody positive Meanwhile, since 1972, 10 to 40 cases of leptospirosis were observed every year. Most of the cases were occupied by the age group from 10 to 19 years of age. The most suspected chances of the infection were supposed to be related to the works in the rice field. Almost 80% of leptospira serovars isolated from the patient was pyrogenes, and autumnalis and hebdomadis followed. Two kinds of vaccines, monovalent vaccine containing pyrogenes and polyvalent one composed of autumnalis and hebdomadis in addition to pyrogenes, were provided by a manufacture. The leptospira strains used in the production of the vaccines were all those isolated in Izena island. The monovalent vaccine was inoculated into about 600 volunteers in 1977 and the polyvalent one into other about 1,000 volunteers in 1978. Thereafter leptospirosis cases clearly decreased in Izena island. And the remarkable serovar specificity in respect of the effect of vaccine was demonstrated. From the results of follow-up, it is infered that the effect of vaccine may persist at least several years.