沖縄県八重山群島におけるマラリア流行と人口変動
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概要
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Influences of epidemic of Falciparum malaria on the population dynamics of communities and families before the introduction of modern medicine for the prevention and treatment of malaria were evaluated in Yaeyama Islands in Okinawa Prefecture. Population growth and structure in a period (1880-1911) in the Meiji era were compared between 4 hamlets each in the highly infected Iriomote Island (M [Main]-Island) and in the non-infected neighboring peripheral islands (P [Peripheral]-Islands). Although malaria was not endemic in P-Islands, the inhabitants of these islands were also exposed to malaria because they temporarily visited M-Island for cultivating rice and collecting forest resources. Changes of population were examined during two successive periods: period I (1880-1903), during which free moving between hamlets was prohibited by the poll tax law; and period 11 (1903-1911), after the abolition of the law. The results are summarized as follows: 1) The prevalence of malaria in all ages of both sexes was prominently higher in M-Island (26.5%) than in P-Islands (3.4%). The difference in prevalence was prominent among children aged 0-9 years: over 70% in M-Island vs. much less in P-Islands. The prevalence among women in the reproductive age was also higher in M-Island than in P-Islands. 2) Both population and number of households in M-Island hamlets slightly decreased (median was -2.7%o/year in population and -1.2%o/year in households) in period I. This decreasing trend was accelerated in period II (-21%o in population and -13 .5%o in households) by emigration. On the other hand, those in P-Islands highly increased throughout both periods (period I, 16%o increase in population and 18%o in households; period II, 11.8%o in population and 4%o in households). The household members in MIsland hamlets was significantly smaller (median was 3.47 in period I and 3.4 in period II) than in P-Islands (4.75 in period I and 5.74 in period II) in both periods. 3) In period I, when migration was restricted, the ratios of number of children aged under 15 years and of older persons over 50 to the adults aged 15-49 were significantly smaller in M-Island than in P-Islands. 4) The vital statistics in period I were estimated by the West type's stable population model. Crude and infant death rates were significantly higher in M-Island than in PIslands. Life expectancy was also significantly shorter in M-Island. No statistically significant difference in crude birth rate was found between M-Island and P-Islands presumably of a larger variation among the hamlets in M-Island than in P-Islands. 5) These results suggest that the population decrease in M-Island in period I was caused by the high death rate in particular among children due to malaria and related complications. In P-Islands, it is inferred that malaria was only prevalent among men of working age, who engaged in inter-insular cultivation. The low death rate among children and high birth rate in P-Islands are attributable to this communal preventive behavior system against malaria. This probably contributed to the high population growth rate. For the malaria control measures of the day, further efforts should be paid to the evaluation of preventive behavior system focused on children and mothers.
- 日本民族衛生学会の論文