The reconsideration of natural history of echinococcosis at Rebun Island.

: It has been believed that the outbreak of echinococcosis at Rebun Island had ceased by 1970. The first patient was diagnosed in 1936 and 131 patients have been authorized as echinococcosis so far. The conference of measures against the outbreak had been organized in 1948 and started to eradicate Echinococcus multilocularis from the Island. Medical examination to detect the patients and the capture and autopsy of dogs and cats had been carried out hard till 1970. At that time, foxes imported from Simusiru Island in the middle Kuriles during the years 1924 to 1926 had already disappeared and it has seemed to be sure that stray dogs and cats might carry E. multilocularis and excrete infectious eggs in stead of foxes. Since we have had no real data concerning the natural history of patients with echinococcosis without any treatments, it can not be recognized the time of infection and the role of dogs or cats on the spread of echinococcosis at Rebun Island. From the new data, it is concluded that the active life cycle of E. multilocularis between foxes and vole might be closed by 1940, since the last patient infected with E. multilocularis was born in 1940 and died in 1945. Furthermore, it is estimated that more than 200 patients (3 to 4% of people at the island) might die from echinococcosis, because of the fact of the unusual increase of mortality of liver disorders and oldness observed during the years of 1940 to 1960. 81 patients with the high possibility of echinococcosis detected from 1937 to 1963 can be added to 131 authorized patients. Surprisingly, it is noticed that the standard deviations of ages of death of 94 patients born in Meiji era (1880-1912) and 59 in Taisho and Showa eras (1912-1940) are 63.16 +/- 11.68, and 34.32 +/- 11.87, respectively. It means that both old and young people might be infected simultaneously but for the long period. There was no difference between the susceptibility of young and old men to E. multilocularis. The numbers of male patients died were more than those of female patients at the ages from 30s to 60s while the number of female died was predominant after 70s. All 13 familial cases of echinococcosis represent that men might bring the infectious eggs into their houses and died earlier by the infection. Thus, the sexual difference might be due to the life style of men who preferred hunting beside fishing. From these results, it is conceivable that the heavy infection of E. multilocularis excreted from foxes might occur from 1925 to 1940 and the peak of the death might be formed during 1940 to 1965. The eradication of foxes might be done by poachers after 1935 and the adaptation of E. multilocularis from fox to dog or cat might not occur readily at Rebun Island.