A MEDICAL GEOGRAPHIKAL STUDY OF AN ENDEMIC DISEASE IN JAPAN

Abstract

Distosomiasis japonica is one of the principal endemic diseases in Japan. The distribution of morbidity shows Yamanashi Prefecture with an annual average of 52 cases, Shizuoka 2, Hiroshima 2, Fukuoka 2 and Saga 3 based on Statistics for the years 19331937. Morbidity in Japan from October 1944 to September 1945 was 1723; Yamanashi had 979 cases (57% of the total), Saga 395 (23%), Fukuoka 324 (14%), Hiroshima 25. The morbidity district of the Kofu Basin in Yamanashi Prefecture is at the confluence of the Kamunashi, Fuefuki and Ara Rivers. The morbidity sections of greatest density in this district are Mimachi, Futakawa and Asai, (all showing more than 24.48%), Okamata, Showa, Yamashiro, Inazumi, Surni-yoshi (Showing 15.9%); Tamahata, Tatomi, and Imasuwa also exhibit high rates. Although the morbidity on the delta of these rivers is at a high rate, arround the Circuiiference of the basin low rates are found. The dis-ease also breaks out on the delta at the confluence of the Ashida and Takaya Rivers in eastern Hiroshima Prefecture. Morbidity districts of the greatest density in this area are Kannabe with an average annual case rate (1949-1951) of 36, Miyuki 23, Yuda 1.0, Senda 6, Michiue 4, Nobeyania 3, and Nakajo 3. The morbidity districts of the Chikugo River in Fukuoka Prefe-cture are Kurume with a 1950-1951. average of 14 cases, Miyanogin 27, Agi-saka 19, Kitano 5, Umata 10, and Miwa 5; those of Saga Prefecture are Tosu 60, Kisato 22, Fumnoto 6, Tashiro 2, and Asahi 6. The Lake Inba district on the delta of the Tone River shows very low morbidity. Distosomiasis japonica spreads according to the pathogenic complex of Distosoma japonicum, Katayama nosophora and the human body. The attack rate varies with age and sex; 12% in age group 11-15, 11% in age group 16-25, and 9-10% for those above age 26. In Saga Prefecture morbidity by sex is 78 for men and 17 for women. The body length of the male of Distosoma laponicum is 16mm while that of the female is 22mm. The body width of the male is 0. 6mm; that of the female is 0.3mm. The eggs, excreted from the human body, grow into Miracidum and enter Kata-yama nosophora of the intermediate host. The length of Katayama noso-phora is 4_??_9mm and the diameter is 1_??_3mm. The snail lives in slow, stagnant streams of the delta; it cannot live in places affected by tides. The parasitic rate of Distosoma japonicum in the.snail varies from place to place in Saga Prefecture; Takada exhibits a rate of 32 0, Maki 38%, and Kisato 43.4, %. Temperature, surface configuration, agricultural practices and the cultural level are important factors amounting for the geographical distribution of the disease. Morbidity in Japan in 1950 was 918 with August 240 (26%), September 156 (17%), July 1.15 (13%), and October 105 (11%). These four months accounted for 67% of the annual morbidity. In winter months the rate is low, the grouch of Distosoma japonicum requiring tempe-ratures of 20_??_35°C. The monthly coefficient of correlation of morbidity and temperature is +0.723. Swampy districts are important geogens, Kata-yama nosophora living in those districts with numerous rivers and lakes such as Lake Inba of the Tone delta, the Kofu basin, the Ashida and Taka-ya deltas and the Chikugo delta. Pathogenic complexes result froir, culti-vation of paddy rice fields in which men work with bare limbs. A high cultural level leads to the destruction of pathogenic complexes while low cultural levels aid their formation.